How to make your Raspberry Pi IP static

raspberrypi-terminal

In this tutorial I will teach you how to make your IP static on Raspbian installation.

This means, every time you turn off and or restart the Raspberry Pi you IP will remain the same.

Ok. Lest do this!

Find your current IP address by running the following command:

hostname -I

or this one

ifconfig eth0

and look at the part where it says inet addr

If we execute:

cat /etc/network/interfaces | grep 'iface eth0'

we will see the following result:

iface eth0 inet dhcp

The eth0 interface (the LAN port on the Raspberry Pi) is set to DHCP, which means it takes his Internet access address from the DHCP server.

This is usually a DHCP server located on your router.

Therefore, the DHCP server is the one that decide the IP addrss of your Raspberry.

To set a static IP, we have to edit the /etc/network/interfaces file. We will replace the text – static with dhcp, and below, will enter our network info.

First lets open this file with the Nano text editor and set the data.

sudo nano /etc/network/interfaces

Once we have opened the file, it is time to make the edits.

iface eth0 inet static
address 192.168.1.99
netmask 255.255.255.0
gateway 192.168.1.1

What did we do?

First we changed the text of iface eth0 inet dhcp to iface eth0 inet static.

Then at the bottom we added a couple of new lines with settings about our network.

The first line is the actual static IP address.

Once you’re done, press CTRL + X then Y and hit ENTER.

If you want to enter e specific DNS server, then run this command:

sudo nano /etc/resolv.conf

and put the new DNS server inside.

Example: nameserver 8.8.8.8

The final step is to restart the network components for all the changes to take effect.

sudo /etc/init.d/networking restart

Attention!

Use /etc/init.d/networking restart if you are using SSH.

The safest method is to simply reboot your Raspberry Pi using:

sudo reboot

Then reconnect with you Raspberry through SSH, but don’t forget to change your IP address to the new one.

Attention!

The other option is to run:

netstat -ar

Once again you have connected with the PI do the following:

ifconfig eth0

to see your new IP in action!

Part 3 of Weather Station with Arduino

In Part 3 of our project – home weather station with Arduino board, comes the most interesting part, at least for me – connecting the sensors and data extraction.

To see working and reporting stations made with setup similar to mine, check out Chris’ and Alan’s pages.

Ok. Lets continue:

The first step is to plug the Ethernet shield in to the main board – gently insert the board on top of the Arduino – nothing special.

* Note – if the station is going to be in a box, put the sensor cable as far away from the board as possible. The main chip of Ethernet shield can get quite hot 42-43 degrees at 22 degrees ambient temperature, which can seriously affect the data.

Once we have the basic modules connected:

  • Connect BMP180 pressure and temperature sensor:
    • SCL to analog pin 5
    • SDA to analog pin 4
    • VDD pin to 5 volts
    • GND to ground
  • Connect the SHT75 temp and humidity:
    • Clock (Pin1) digital pin 2
    • Data (Pin4) digital pin 3
    • Vcc (Pin2) to pins with 5V
    • GND (Pin3) to ground.
    • For DHT11 sensor linking use the same order
  • Connect the rain sensor:
    • A1 analog pin 1
    • Vcc pins to 5 volts
    • GND to ground.

Sorry I didn’t took any photos when I made the project, but my test version of the staton looked similar to this one:

Arduino board

Once we connect all the sensors the only thing that is remaining is to write the code. Some sensors require a library, for example BMP180 requires one, which can be downloaded from HERE.

Below is code that I wrote with comments about it.

What the code does, is printing the results of the sensors on the serial monitor (Tools > Serial Monitor), as well as displaying the data trough a Web server to local IP address, on minimalist look web page, so that you can style it later.

#include <Wire.h>
#include <SPI.h>
#include <Ethernet.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BMP085_U.h>
#include <Sensirion.h>
     
/*    
   Connections [BMP180]
   ===========
   Connect SCL to analog 5
   Connect SDA to analog 4
   Connect VDD to 5V DC
   Connect GROUND to common ground

   Connections [SHT75]
   ===========
   Connect Clock(Pin1 - White) to 2 (digital)
   Connect Data(Pin4 - Yellow) to 3 (digital)
   Connect Vcc (Pin2 - Red) to 5V DC
   Connect GND (Pin3 - Black) to common ground
*/
/*Sensirion SHT75 Constants*/
const uint8_t dataPin =  3;              // SHT serial data
const uint8_t sclkPin =  2;              // SHT serial clock
const uint32_t TRHSTEP   = 5000UL;       // Sensor query period
const int rainMin = 0;     // rain sensor minimum
const int rainMax = 1024;  // rain sensor maximum

Sensirion sht = Sensirion(dataPin, sclkPin);
 
uint16_t rawData;
float temperature;
float humidity;
float humidex;
float dewpoint;
 
byte measActive = false;
byte measType = TEMP;
 
unsigned long trhMillis = 0;             // Time interval tracking

/*Sensirion SHT75 Constants END*/

Adafruit_BMP085_Unified bmp = Adafruit_BMP085_Unified(10085); //BMP180 code
/*OneWire  ds(7);  // on pin 2 (a 4.7K resistor is necessary)*/
float celsius = 0; // global temperature variable
float pressurekPa = 0; //global pressure variable

//Ethernet setup >
byte mac[] = {
  0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
};
IPAddress ip(192, 168, 1, 200);
IPAddress gateway(192, 168, 1, 1);
IPAddress subnet(255, 255, 255, 0);
EthernetServer server(80);

void setup(void) 
{
  Serial.begin(9600);
  /*SHT75 SETUP:*/
  delay(15);                             // Wait >= 11 ms before first cmd
// Demonstrate blocking calls
  sht.measTemp(&rawData);                // sht.meas(TEMP, &rawData, BLOCK)
  temperature = sht.calcTemp(rawData);
  sht.measHumi(&rawData);                // sht.meas(HUMI, &rawData, BLOCK)
  humidity = sht.calcHumi(rawData, temperature);
  dewpoint = sht.calcDewpoint(humidity, temperature);
  logData();
  /*SHT75 SETUP END*/
  
  /* Ethernet config */
  Ethernet.begin(mac, ip);
  server.begin();
  Serial.print("server is at ");
  Serial.println(Ethernet.localIP());
  
  /* Initialise the BMP180 sensor */
  if(!bmp.begin())
  {
    /* There was a problem detecting the BMP180 ... check your connections */
    Serial.print("Ooops, no BMP180 detected ... Check your wiring or I2C ADDR!");
    while(1);
  }

}

void loop(void) 
{
    /* Temp readings: */
    /*SHT75 loop: */
      unsigned long curMillis = millis();          // Get current time
     
      // Demonstrate non-blocking calls
      if (curMillis - trhMillis >= TRHSTEP) {      // Time for new measurements?
        measActive = true;
        measType = TEMP;
        sht.meas(TEMP, &rawData, NONBLOCK);        // Start temp measurement
       
        BMP180();                                  // Pressure measurement
        
        trhMillis = curMillis;
      }
      if (measActive && sht.measRdy()) {           // Note: no error checking
        if (measType == TEMP) {                    // Process temp or humi?
          measType = HUMI;
          temperature = sht.calcTemp(rawData);     // Convert raw sensor data
          sht.meas(HUMI, &rawData, NONBLOCK);      // Start humidity measurement
        } else {
          measActive = false;
          humidity = sht.calcHumi(rawData, temperature); // Convert raw sensor data
          dewpoint = sht.calcDewpoint(humidity, temperature);
          
          //humidex code:
          float h,e; //humidex and other
          e = 6.11 * exp(5417.7530 * ((1/273.16) - (1/(dewpoint + 273.15)))); 
          h = (0.5555)*(e - 10.0);
          humidex = temperature + h;
          logData();
        }
      }
    /*SHT75 loop end*/
    
    
  /* Web server: */
    EthernetClient client = server.available();
  if (client) {
    Serial.println("new client");
    // an http request ends with a blank line
    boolean currentLineIsBlank = true;
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();
        Serial.write(c);
        // if you've gotten to the end of the line (received a newline
        // character) and the line is blank, the http request has ended,
        // so you can send a reply
        if (c == '\n' && currentLineIsBlank) {
          // send a standard http response header
          client.println("HTTP/1.1 200 OK");
          client.println("Content-Type: text/html"); // text/html
          client.println("Connection: close");  // the connection will be closed after completion of the response
          //client.println("Refresh: 5");  // refresh the page automatically every 5 sec
          client.println();
          //client.println("<!DOCTYPE HTML>");
          //client.println("<html>");
          // output the data
            client.print(temperature);
            client.print(" ");
            client.print(humidity);
            client.print(" ");
            client.print(pressurekPa);
            client.print(" ");
            client.print(dewpoint);
            client.print(" ");
            client.print(humidex);
            client.print(" ");
            client.print(analogRead(A1));
            //client.println("<br />");
          
          //client.println("</html>");
          break;
        }
        if (c == '\n') {
          // you're starting a new line
          currentLineIsBlank = true;
        }
        else if (c != '\r') {
          // you've gotten a character on the current line
          currentLineIsBlank = false;
        }
      }
    }
    // give the web browser time to receive the data
    delay(1);
    // close the connection:
    client.stop();
    Serial.println("client disconnected");
  }
}



void BMP180() {
  delay(1500);
  /* Get a new sensor event */ 
  sensors_event_t event;
  bmp.getEvent(&event);
 
  /* Display the results (barometric pressure is measure in kPa) */
  if (event.pressure)
  {
    /* Display atmospheric pressue in kPa */
    Serial.print("[BMP180]Pressure:    ");
    Serial.print(event.pressure / 10);
    pressurekPa = event.pressure / 10;
    Serial.println(" kPa");
         
    /* First we get the current temperature from the BMP085 */
    float temperature;
    bmp.getTemperature(&temperature);
    Serial.print("[BMP180]Temperature: ");
    Serial.print(temperature);
    Serial.println(" C");

    /* Then convert the atmospheric pressure, and SLP to altitude         */
    /* Update this next line with the current SLP for better results      */
    float seaLevelPressure = 1022 /*SENSORS_PRESSURE_SEALEVELHPA*/;
    Serial.print("[BMP180]Altitude:    "); 
    Serial.print(bmp.pressureToAltitude(seaLevelPressure,
                                        event.pressure)); 
    Serial.println(" m");
    Serial.println("");
  }
  else
  {
    Serial.println("Sensor error");
  }
}

    void logData() {
      Serial.print("[SHT75]Temperature = ");   Serial.print(temperature);
      Serial.print(" C, Humidity = ");  Serial.print(humidity);
      Serial.print(" %, Dewpoint = ");  Serial.print(dewpoint);
      Serial.println(" C");
      Serial.print("Humidex: ");
      Serial.println(humidex);
      Serial.print("Water Level: ");
      Serial.println(analogRead(A1));
    }

The above code will make a Web server on 192.168.1.200, where on a single line you will see the data from all sensors.

These data can now be taken in order to generate graphics or store it inside a file or whatever you are most comfortable with. I personally use Linux machine that draws graphics using munin software (based on rrdtool). There are thousands of solutions for drawing graphics; you just have to look at the options.

And that’s it.

DIY Home Arduino Weather Station – Part 2

Once you got all the necessary materials in Part One, it is time to proceed with the preparation of their programming.

But before that we have to prepare the software that will program the Arduino weather station.

The latest version of the software can be downloaded from HERE. However, because our Arduino is not original we need to download additional drivers. Drivers for Arduino chipset CH340 / CH341 can be downloaded from HERE. If you do not know how to install drivers, you can find instructions on their official website.

On the step where you select the .inf file, specify the file you’ve just downloaded and unzipped form the link above.

Once you have everything, start the IDE, which looks like this:

arduino_ide

In the Tools menu, go to submenu Board and select “Arduino / Genuino Uno” or any board you have.

In Port submenu select ports that display the board. Here is the moment to point out that to complete this step, the board must be connected via USB cable to the computer.

If this submenu is gray, it means that your drivers are not installed correctly. DO NOT install drivers that come with the IDE unless you have the original board – boards that are cheaper (mine is) are not original and therefore they need drivers that are mentioned above.

Let’s look at the structure of code that will write:

Block setup (void setup () {}):

Here we introduce a code that will be executed once, when the board is turned on or after pressing restarting the reset button.

Block setup (void loop () {}):

Here we introduce a code that will be repeated regularly until the board works.

* If you want to use global variables to initialize libraries for certain sensors, etc., please fill out these two blocks.

In the menu File> Examples> 01.Basics has simple examples that can be tested for the first steps with the board (for example, Read Analog Voltage)

In Part Three will move to connect the sensors to the main board, and to retrieve data from.

To part 3

DIY Home Weather Station

It probably occurred to a lot of people, one time or another, to make a home weather station. This is especially true for those who need something specific or just love to tinker with electronics.
This kind of device can track the weather at your village, backyard, or inside your home. In my case the need was caused by the fact that in our city there is no weather station and data that I have is actually from another city

Before we continue lets see the main operational features:

  • It will measure temperature, humidity, atmospheric pressure and intensity of rainfall through sensors connected to Arduino board (small PCB controller – sounds scary, but is not);
  • It will measured dew point and humidex (temperature as felt by the human body) based formulas with data from other sensors;
  • Will make data available in on the Internet. For visualization we will use graphics that are drawn by a server that will collects the data;

What knowledge do we needed?

  • Minimum experience with soldering iron;
  • Minimum programming knowledge – the controller is programmed with IDE in C language. All sensors that we are going to use, have libraries with code, and you have to adjust them according to your needs;

What materials do we need?

Arduino Uno
Arduino Uno board – the version with soldered chip is available for around $10

temp sensor
Temperature and humidity sensor – I will use SHT75, because I have one, but I recommend using DHT11 / DHT22 (pictured below) – the price is $6 – $5

pressur sensor
Sensor for atmospheric pressure BMP180, manufactured by Bosch – price again is around $5 – $6 . There is a built-in temperature sensor, but is not quite accurate – if you do not interfere with deviations of 2-3 degrees may very well be used

ETH Sheild
Arduino Ethernet Shield

rain sensor
Rain sensor

All sensors can be found cheaper on Chinese websites, if you wait for delivery.

In part two we will configure our IDE which we are going to use to program the Arduino

August, September, and October Weather Discussion Archive – Retrospect

 

Wilma

October 17 2005 – 18:30 UTC

Tropical Storm Wilma is the 21st named storm of this incredible 2005 hurricane season. 2005 is now tied with the 1933 season for the most named storms in a single year. Wilma has strengthened steadily over the last 24 hours, and that should continue for an additional 24 hours. Sea surface temperatures and oceanic heat content are conducive for rapid strengthening, but the favorable anticyclone aloft has shifted to the west and is now anchored just east of the Yucatan coastline. As a result, the northerly clockwise flow around the Watsonwille and  Dallas is knocking down convection over the surface circulation with 10-20 knots of shear. It is only a matter of time until Wilma positions itself underneath this ridge, and rapid intensification will likely begin once that happens. Category three of four status may be Wilma’s peak intensity in the northwest Caribbean Sea before being drawn north by an approaching trough. Once the upper level trough begins to interact with the hurricane, upper level southwest winds may begin to weaken the cyclone to some extent.

Continue reading August, September, and October Weather Discussion Archive – Retrospect

IWIC 2005 Atlantic Basin Hurricane Season Forecast

I. Introduction

This is the third seasonal hurricane forecast issued by the Independent Weather Information Center. The seasonal forecasts released prior to June of 2003 and 2004 both demonstrated a high degree of skill. However, no long-term forecast has ever been absolute, and a higher degree of accuracy is desired this season. This forecast is an unofficial one, and therefore we are not liable for one’s actions based upon the information being presented. Please read our disclaimer.

The data and research used to establish this independent forecast was obtained during the months of October to May. The primary parameters that are known to affect the frequency and steering of tropical cyclones in the Atlantic Basin have been closely analyzed throughout the offseason. A thorough explanation and forecast of these factors are outlined. In addition, 55 years of climatological evidence have been included to coincide with the anticipated 2005 summer pattern over the northern hemisphere. All of the aforementioned data has been utilized to not only forecast seasonal tropical cyclone activity, but also month-by-month activity, regional activity, and landfall probabilities. It should be noted that offseason developments prior to June 1 or ensuing November 30 will not be included within the verification of this seasonal forecast.

II. El Nino Southern Oscillation

The El Nino Southern Oscillation, commonly referred to as ENSO, is the most important parameter concerning Atlantic Basin tropical cyclogenesis. ENSO is most notably characterized by significant variation of sea surface temperatures anomalies, or SSTAs, in the equatorial Pacific Ocean, though alterations in sea level pressure, trade winds, and convection are also observed. Warm SSTAs are associated with El Nino episodes, whereas La Nina episodes correspond with cool SSTAs. If SSTAs are neither warm nor cool, ENSO is considered neutral.

Once an El Nino event takes hold, strong upper level westerly winds dominate the low latitudes of the Atlantic Basin. As a result, hurricane development from tropical waves and disturbances along the intertropical convergence zone is typically suppressed. In the mid-latitudes, a higher frequency of upper level troughs and other dynamics that support the development of cutoff lows is typical. High latitude tropical and subtropical activity is thus increased during El Nino events. The reverse is true for La Nina. There is only a small difference between the number of named storms in an El Nino versus a La Nina, but far more hurricanes and intense hurricanes are observed in a La Nina or even neutral ENSO conditions than in an El Nino event.

Current Status of ENSO

ENSO has been in a predominantly warm state since the late spring of 2002. During that year, SSTAs in ENSO Region 3.4 peaked in October and November with anomalies exceeding 1.5 degrees Celsius. By spring 2003, the SSTAs began to cool, and a return to the climatological average transpired. Nevertheless, a secondary warming phase occurred in the summer and El Nino returned. Similar fluctuations ensued in 2004, with a slight moderation period in the spring followed by a warming trend during the latter half of the year. In fact, SSTAs rose to 0.9 degrees Celsius from August through December, and El Nino critera was met for a third straight year.

By late December 2004, SSTAs in the equatorial Pacific Ocean began to show signs of moderation. The 30-day Southern Oscillation Index rose to neutral territory in January for the first time since May 2004. The 30-day Southern Oscillation Index, or SOI, is defined by the monthly sea level pressure differential between Tahiti and Darwin, Australia. The SOI is generally a good indicator of ENSO’s status. Persistent negative values correspond with El Nino, the opposite for La Nina. When ENSO is in a neutral state, the SOI tends to fluctuate between negative and positive values more often. ENSO region 3.4 SSTAs decreased from 0.9 to 0.6 degrees Celsius by February. All indices were beginning to suggest that a return to neutral ENSO conditions was imminent within the next few months. That changed in February when a strong pulse of the Madden Julian Oscillation, MJO, moved across the western Pacific Ocean and enhanced parameters needed for tropical cyclogenesis. The South Pacific Basin became extremely conducive for tropical cyclone formation. Super cyclones Nancy, Olaf, and Percy, which were extensively analyzed and discussed here at IWIC, all developed during the MJO pulse. The MJO pulse coincided with one of the most intense South Pacific Basin cyclone seasons in recorded history, which in turn helped to enhance a Westerly Wind Burst, or WWB, that traveled across the Pacific Ocean. As a result, the SOI plummeted to -52 on February 26, the lowest daily measurement recorded since the extreme El Nino in 1997. Such WWBs can enhance warm depth temperature anomalies, or DTAs across the equatorial Pacific Ocean, which then surface off the coast of Peru two to three months later. Fears of a moderate or strong El Nino returning by summer began to run rampant. However, the sudden drop in the SOI was masked by the South Pacific Basin super cyclones, and other signs of El Nino development were not present.

The WWB, which was triggered by the MJO and intense cyclones, did in fact create a Kelvin wave, and warming beneath the surface became apparent by the month of March. Some warming of the ocean’s surface in the Nino regions 1 and 2 within one to two months was expected. By late April and early May, weekly ENSO region 1.2 SSTAs rose from -1.1 to 0.5 degrees Celsius. A continued rise in subsurface temperatures would suggest that El Nino formation is underway, but that is not the case this time around. The warm pool below the ocean surface has all but reached the surface and moderated, and a new WWB just as intense as the one in observed in February is unlikely.

Climatology

Climatology is one of the best available tools in ENSO prediction. 1950 to 2004 seasonal ENSO region 3.4 SSTAs were utilized to obtain these following statistics. The 2002 through 2005 warm ENSO episode has been one of the longest-lasting since 1950, second only to the 1991 to 1995 episode. This warm biased ENSO period lasted longer than ten previously recorded episodes. The probability of warm equatorial Pacific Ocean SSTAs lasting another three to six months is nine percent based on those statistics. In addition, there have been 15 El Nino events that persisted through the winter months, and exhibited signs of weakening between December and April the following year. Such has been the case so far in 2005. Only three out of those 15 years, 20 percent, experienced El Nino conditions during the climatological peak of hurricane season. Furthermore, the analogous ENSO years for the December to April period, 1970, 1978, 1988, and 1995, all experienced significant ENSO cooling throughout the spring and summer. La Nina conditions were present during the 1970 and 1988 hurricane seasons while 1978 and 1995 were cool biased. Climatology highly argues against a prolonged El Nino episode lasting well into the 2005 hurricane season. There is even a slight chance of cool biased ENSO conditions by the peak, but a return to neutral conditions is much more likely than either an El Nino or La Nina.

ENSO Prediction Models

Coupled and statistical ENSO models have been in use for several years to try to accurately predict the evolution of ENSO up to eight months in advance. Each individual model has a bias to one extent or another, and at certain times of the year. Therefore, it is better to look at the model consensus as a whole, and more importantly, the model consensus trend. This spring, the average of all the models combined is a slight warm bias. Some, such as the POAMA, were recently forecasting a weak to moderate El Nino to develop over the summer. These select models have been trending cooler however, and again, it is the trend that is really important. The rest of the models have been consistent on an overall neutral ENSO, though it is worth noting that the CLIPER, a relatively good statistical model, has trended to show nearly a weak El Nino during the hurricane season.

ENSO Models September 2005 December 2005
POAMA Warm Warm
CPC Warm Neutral
ECMWF Neutral Not Available
UKMO Cold Not Available
LDEO Neutral Neutral
NCEP Neutral Neutral
NOAA LINEAR INVERSE Neutral Neutral
SCRIPPS/MPI Neutral Neutral
NSIPP/NASA Neutral Neutral
JMA Warm Not Available
CLIPER Neutral Neutral
SSES Neutral Not Available

2005 Summer ENSO Forecast

There are clear signals that point towards a neutral ENSO state during the 2005 hurricane season. After the WWB, the DTAs have resumed to a slightly cool state and with little signs of warming further west. This trend does not match the spring state of DTAs in years where an El Nino developed later on such as last year. Furthermore, the model consensus and trend similarly points to a late summer ENSO with a ONI value between -0.5 and 0.5 degrees Celsius. Climatological ENSO statistics would also argue against any El Nino, and if anything it would favor a La Nina. Finally, it is worth noting that three the best five global predictors for predicting ENSO a half year to year in advance, courtesy of Seseske 2004, suggest neutral to cool ENSO conditions, whereas the other two support a warm ENSO. Taking all of this information into account, yet another El Nino regeneration appears very unlikely this year. A La Nina is improbable as well, mostly due to the lack of stronger cool DTAs and model support. The currently warm-biased ENSO, residual from the weak El Nino event that recently dissipated, should continue to slowly relax over the summer and fall. Although there is some uncertainty regarding the bias towards the end of the year, spot-on neutral ENSO conditions should prevail during the heart of the 2005 Atlantic Basin hurricane season. This will neither help nor inhibit tropical cyclone formation.

III. Quasi-Biennial Oscillation

The Quasi-Biennial Oscillation, QBO, is a periodic variation in the direction of stratospheric winds across the deep tropics. The two phases, easterly and westerly, generally last from 12 to 16 months, with the easterly phase often having a slightly longer duration. The exact mechanism in which the QBO influences activity is not yet completely understood, but it is suggested that the QBO is responsible for at least some variation in upper level vertical wind shear in the tropical Atlantic Basin.

Aside from the fact that its exact role is a mystery, there has been significant dispute among the amateur and professional meteorological community as to whether the QBO is truly a crucial factor involving Atlantic Basin hurricane activity. Dr. William Gray at Colorado State University cites that the influence of the QBO has not been very noticeable since the multi-decadal upturn of activity, which began in 1995. After further investigation, it has been decided that the QBO will still be considered a significant parameter in this forecast. Climatological research shows that the QBO particularly influences major hurricane frequency in the tropical Atlantic Basin, with a relatively insignificant impact on the total amount of named systems and hurricanes. The westerly phase of the QBO tends to increase the number of major hurricanes while easterly years usually have an average number of intense hurricanes. In the past ten years, the average number of major hurricanes is 3.8 for both the westerly and easterly phases of QBO, respectively. However, two of the five westerly QBO years had a moderate to strong El Nino present. None of the easterly QBO seasons had a noticeable El Nino. If one were to eliminate 1997 and 2002, the new major hurricane average for westerly QBO years is increased to 5.3. Based on this recent ten year research sample, combined with the well exhibited correlation in earlier years, it is deduced that the QBO does affect major hurricane activity in the Atlantic Basin.

Unlike ENSO, the QBO’s alternation between phases is timely, making it quite simple to forecast. Last hurricane season, the westerly phase of the QBO peaked in May, with a value of 13. Since then, it slowly declined and just recently this year has transitioned to the easterly phase. The QBO will continue to fall and peak later this year, with the next transition not occurring until sometime in 2006. Therefore, the QBO is judged to be a suppressing factor for major hurricane activity in the Atlantic Basin this season.

IV. Atlantic Thermohaline Circulation

The Atlantic Thermohaline Circulation, or ATC, is a density-driven circulation in the Atlantic Basin that undergoes cycles on decadal timescales. It has been proven that the ATC influences Atlantic Basin hurricane activity. When the ATC is in its warm or strong cycle, hurricane activity is increased. During the strong cycle of the ATC, the most notable consequence is warmer SSTAs across the tropical Atlantic Basin, which provides more energy for a tropical storm or hurricane to sustain deep convection. Additionally, lower vertical wind shear and sea level pressure anomalies, or SLPAs, are typically observed across the Atlantic Basin with a strong ATC. The exact opposite is true for the weak or cool phase of the ATC, which is inhibiting to tropical cyclone formation. From the mid 1920s through the late 1960s, the ATC was running strong for the most part, and as a consequence, hurricane activity increased during that period. The ATC shifted to its weaker state in the early 1970s, and that cycle lasted through the early 1990s. A sharp decrease in tropical cyclogenesis was noted. Since 1995, the ATC has shifted back to the strong cycle, which explains the significantly above average hurricane seasons that have occurred over the past ten years. However, even during the ATC’s warm phase, it does occasionally fluctuate for several months. These small fluctuations are difficult to forecast in advance, but observing SSTAs in the Mean Development Region over a monthly period is an easy way to monitor such trends.

Since mid 2003, the SSTAs in the eastern Atlantic Basin have for the most part remained much warmer than average. Notable warm SSTAs have been especially noted over the Mean Development Region this past winter and spring, with monthly values reaching as a high as 0.85 degrees Celsius above average. SSTAs have been just as consistently warm around the Azores and Canary Islands, a tell-tale location of the ATC’s mode. In 2002, there were already signs of the weakening ATC by this time of the year, not only in the SSTAs but also the very positive North Atlantic Oscillation that was setting up. Since neither is the case, a cooling scenario similar to what happened that year is highly unlikely. Therefore, a continued strong ATC and associated warm SSTAs is anticipated throughout the remainder of the year, acting as a robust enhancing factor for tropical cyclone formation, particularly that in the Mean Development Region.

V. North Atlantic Oscillation

The North Atlantic Oscillation, or NAO, is the fluctuation in 500 millibar heights in the northern Atlantic, primarily between western Europe, Iceland, and Greenland. Despite the fact that the difference in phases has little to no impact on seasonal tropical cyclone frequency, the NAO has been shown to have an important role in determining the general steering pattern across the Atlantic Basin. One problem that has prevented reliable techniques in forecasting the NAO months in advance is that it is extremely variable on a monthly and even weekly basis. It would be foolish for us to try to forecast its evolution through the rest of the year without the proper understanding that most have yet to acquire. However, our 55-year climatology does indicate that winter and spring NAO values may influence the steering that sets up during the hurricane season via lag influences.

The NAO was predominantly positive this past winter, although it dropped very low in February and March, with the monthly mean indices standing at -1.33 and -2.76 respectively. It was less so negative in April and has been lingering closer to normal so far this month. Excluding other steering factors, a positive NAO in the winter will modestly correlate with a stronger ridge over the central Atlantic Basin and a stronger trough offshore the United States east coast during the hurricane season. One of our interesting finds was that out of all the tropical cyclones since 1950 that moved westward through the entire Caribbean Sea without dissipating, only ten percent of them occurred in a season that had a positive NAO the prior winter. If this research is indeed a true correlation and not just a coincidence, it suggests that storms forming east of the Lesser Antilles this season will either dissipate or more likely recurve east of 80 degrees west rather than tracking all the way into Central America or the Gulf of Mexico.

VI. Pacific Decadal Oscillation

The Pacific Decadal Oscillation, hereby referred to as the PDO, is a multi-decadal pattern of high and low pressure systems in the northern Pacific Ocean, sometimes seen as a longer-term version of ENSO. However, unlike ENSO, the PDO index is calculated by spatially averaged monthly SSTAs over the northern portions of the Pacific Ocean, not the equatorial. In terms of its variability, the PDO is most similar to the ATC, given that it too fluxes on a multi-decadal basis between a cool and warm cycle. Also like the ATC, the PDO sometimes temporarily swings for a month or even a few years until returning to its dominant cycle phase. The cycle of the PDO switched to warm around 1977, and began showing signs of reverting back to the negative cool phase in the late 1990s. However, since late 2002, the PDO has been predominantly positive; very much so over the past few months. It is uncertain whether the cool PDO that lasted a few years after 1998 was a deviation from the ongoing warm phase, or the warm PDO in the recent few years is a temporary fluctuation away from the new cool phase. One option is that the PDO is in a transitional stage, meaning that it is in a somewhat lengthy process of switching.

Regardless of the dominant cycle the PDO is in, it has been positive this past winter and spring. Some of our climatological research suggests that the February to March PDO values combined with winter tropical Atlantic Basin SSTAs has a lag correlation on the Atlantic Basin steering and tropical cyclone track patterns. In the 55 years that were sampled, it was noticed that in years when the PDO was positive and the winter Atlantic SSTAs were generally cool, three in every four storms that developed in the Mean Development Region recurved out at sea. In the seasons with the opposite conditions, a cool PDO and warm Atlantic Basin SSTAs, about every other storm recurved. Although the relationship is not tight enough to explain a large amount of the track variance, it is worth taking into consideration. This year, the winter SSTAs in the tropical Atlantic Basin were considerably above average, but the PDO was also positive in February and March. 2005 therefore falls in the middle range where the PDO and the Atlantic Basin SSTAs will have opposing lag connections. At face value, this argues against the extremes of having several low latitude tropical cyclones track into the Gulf of Mexico or all of the storms staying harmlessly at sea. However, to obtain a more clear-cut understanding of the track pattern, other predictors have to be examined.

VII. Geopotential Heights and Precipitation

One way to gain an accurate representation of the steering pattern during the upcoming hurricane season is by observing geopotential heights during the April to May timeframe. Geopotential height refers to the potential energy per unit mass of a body as a result of the earth’s gravitational field, but to explain it easier, low geopotential heights usually correspond to low pressure and vice-versa. The 500-millibar level of the atmosphere is used as it is a fair compromise between pressure anomalies in the upper and lower portions of the troposphere. The geopotential height pattern over the past 60 days has been characterized by low height anomalies over the eastern part of the United States and in the central Atlantic Basin just west of the Azores. High height anomalies, on the other hand, have been noted south of the Canadian Maritimes and just off the Iberian Peninsula. This particular regime is concerning for some, as we will explain a little further down.

Another fair, though more indirect indicator of the mean ridge and trough positions comes from analyzing precipitation totals by state across the United States. Precipitation average departures for spring similarly show correlation with the tropical cyclone track pattern in the succeeding hurricane season. Since March, the eastern seaboard of the United States in general has been predominantly wetter than average. This relates nicely to the overall low geopotential height anomalies observed over the same area. However, areas west of the Mississippi River, particularly Texas and the Great Lakes region, have had below average precipitation in the same time period.

From observing the geopotential heights and precipitation departure data, it can be deduced that frequent trough activity has occurred around the United States eastern seaboard over the past three months at least. The Bermuda High, the dominant steering feature for western Atlantic Basin tropical cyclones, has been centered offshore for the most part. Also, there has been more ridging in the central and southern portions of the United States. Climatologically, it is this type of pattern that favors one or more hurricane strikes along the United States east coast. The stronger than normal Bermuda High that is setting up will push any storm that moves under it westward. However, the frequent troughs along its western periphery will make it difficult for a storm to remain on a westward course into the Gulf of Mexico, therefore leaving the areas from the Keys up through New England more vulnerable for a major strike than anywhere further west. This hypothesis was tested by looking at the spring rainfall and height anomalies for our seven analog years. All but one, 2001, featured a hurricane hit along the United States east coast. Scarily enough, all except 1960 and 2001 also had a tendency for above average precipitation and low geopotential heights in that region. 1960 is even a borderline case since it was more average than either dry or wet across the Mid-Atlantic states. Although this steering pattern will not favor long-tracking storms moving westward into the Gulf of Mexico, tropical cyclones that do form in the Gulf of Mexico may tend to move west due to the ongoing tendency of a stronger ridge over Texas and the central Plains.

VIII. Selected Analog Years

Analog years are a necessity when determining long range forecasts. Today’s available weather tools, such as long range forecast models, can only make predictions with a fair amount of skill so many weeks and months in advance. A decent-sized dataset of climate history, or climatology, provides either reassurance or a reason to reassess the conclusion of what has already been analyzed. After making an assessment of the main factors, a limited number of years, analog years, that best match the forecast summer pattern are selected. More so than anything else, years with a predominantly neutral ENSO, easterly QBO, and warm ATC were selected. The trends with ENSO and ATC, along with the NAO and PDO, were also taken under consideration. The analog years chosen for the 2005 hurricane season are below.

Analog Year Named Storms Hurricanes Major Hurricanes
1952 7* 6 3
1958 10* 7 4
1960 7* 4 2
1989 11 7 2
1996 13 9 6
2001 15 9 4
2003 16 7 3

*Recorded named storm amounts prior to the satellite era are suspect. Some may have been missed.

However, all of those years had at least one difference in the pattern than what is setting up this year. The ATC was not nearly as strong in 1960 compared to this year, and it was temporarily weak in the beginning of 1952, 1989, and 2001. A weaker ATC even before the season begins has noticeable implications on the steering pattern and deep Atlantic Basin conditions during August and September. Also, 1989, 1996, and 2001 had a La Nina episode the preceding winter, which is the opposite of the weak El Nino that was present in the beginning of 2005. The El Nino that formed in 1957 did not dissipate until the summer of 1958, which posed a slight lag influence on that season, and warm bias ENSO conditions rebounded during the fall of 2003, helping to weaken tropical cyclone activity in the latter portion of that season. None of the analog years are perfect, but taking everything into account, the top three of the list are 1958, 1996, and 2003.

IX. Activity By Region

The Atlantic Basin has been divided into separate regions so that the amount of tropical cyclone activity in each sector can be analyzed.

Mean Development Region

The Mean Development Region is the area between the Lesser Antilles and the western coast of Africa south of 20 degrees north. This is where tropical waves traverse and often develop into hurricanes either in the region itself, or later on in the Caribbean and western Atlantic Basin, hence its name. The extremely warm SSTAs in the Mean Development Region this spring will set the stage for lower SLPAs and more energy to sustain deep convection. Furthermore, the predominantly negative NAO since February also translates to a weaker Azores High, which in turn reduces shear across the area. Also worth noting is the strength and mean position of the intertropical convergence zone, or ITCZ. The ITCZ is essentially a zonal area of low atmospheric pressure and ascending air located around 10 degrees north during the season, and often spins off tropical cyclones when it is not too close to the equator. Although it has been suggested that an easterly QBO suppresses the ITCZ to some degree, the lack of an El Nino combined with the weaker Azores High and warmer SSTAs should still allow for a more northward-shifted and stronger ITCZ this season.

Taking the above into consideration, an above average level of tropical cyclone activy in the Mean Development Region is likely this year. All of our analog years except 1960 saw at least five tropical systems develop in this area. The problem with 1960 as well as 2001, which did not see any hurricane form in the Mean Development Region, can be best explained by the temporarily relaxed ATC during those summers. This was a strong reason why SLPAs in the deep Atlantic Basin were increased in both years. In 1960 the frequency of Mean Development Region storms was lessened, whereas in 2001 the less favorable conditions put a hamper on the intensity. However, such an ATC relaxation is not the case this year, and therefore 2005 should not be faced with that kind of problem. Five to six named storms are forecasted to originate in the Mean Development Region, with three to four being hurricanes, and one to two of those achieving major hurricane status in the area.

Subtropical Latitudes

The subtropical area of the Atlantic Basin is generally more favorable than the Mean Development Region in years with El Nino or cool ATC conditions. Neither is the case this year, so activity in the high latitudes will be restricted to at least some extent. Nonetheless, a warm ATC and neutral ENSO combination is climatologically not too unfavorable. The amplified trough and ridge pattern that is expected to prevail during the season also implies better dynamics for cut-off lows to develop, especially early and late in the season. Furthermore, there is always the possibility of a highly amplified tropical wave not developing until it is in close to the Bahamas, an uncommon but not unseen example of tropical-originating development in this region. A simple look at our analog years reveals a spread of diversity in subtropical tropical cyclone activity, but given the trough and ridge setup combined with the neutral ENSO and warm Atlantic Basin SSTAs, the area should be slightly more favorable than usual this year. Three to four named storms, with one to two being hurricanes, are forecasted to form above 20 degrees north in the basin in 2005.

Caribbean Sea

We first begin with the eastern Caribbean Sea, often referred to as the dead zone of the tropical Atlantic Basin. This nickname was earned by strong southwesterly shear often in the area due to the summer and autumn presence of the Tropical Upper Tropospheric Trough, or TUTT. This feature, while almost always there, is stronger in some seasons than others, thus having implications on approaching tropical cyclones. Because of the TUTT, very rarely do tropical cyclones actually form in this region. It has been hypothesized that the easterly phase of the QBO could strengthen the TUTT over the summer. However, SSTAs in the eastern Caribbean Sea have been extremely warmer than normal over the past few months. This will aid the barotropic nature of the atmosphere, which in turn will cancel and rule over any influence that is exhibited by the QBO. Therefore, a slightly weaker than normal TUTT is likely this season. Conditions in the eastern Caribbean Sea will not be completely hostile, but activity will likely be on the light side because of the lack of storms expected to move into the area.

In the western Caribbean Sea, conditions are usually more favorable. The problem is, in 2005 most of the storm activity in this region will probably come from in-situ development, rather than a system moving into it from the eastern Caribbean Sea. This will limit the net total of activity, but the low SLPAs and exceptionally warm SSTAs since winter could assist in early season development. Later in the season, there is some concern for a major hurricane to develop in the western Caribbean Sea, as we will explain further down in the monthly section. All in all, the Caribbean Sea as a whole should be somewhat more active than usual with three to four named storms, two to three hurricanes, and possibly one major hurricane.

Gulf of Mexico

We do not anticipate much activity in the Gulf of Mexico during 2005. As we outlined earlier, the winter and spring statuses of the NAO, PDO, and Atlantic Basin SSTAs do not support the idea of storms moving through the Caribbean Sea and into the Gulf of Mexico due to a stronger trough along the United States east coast. However, data suggests that there will not be many in-situ Gulf of Mexico systems either. One interesting correlation we found this offseason is that when the March through April SLPAs off the Mid-Atlantic states coastline are positive, more activity is generally observed in the Gulf of Mexico the succeeding hurricane season. In fact, after separating the past 55 years into two groups based upon this, and then omitting a few outliers that all had the same unrelated conditions present, the average number of named storms, hurricanes, and major hurricanes were all doubled in the positive Mid-Atlantic SLPA years. A reason for this relation could be that higher SLPAs equate to a stronger ridge in the eastern United States, which helps guide tropical cyclones into the Gulf of Mexico and ventilates ones that develop there. Reversely, negative SLPAs are more indicative of a trough, which may induce a an unfavorable southwesterly flow across the Gulf of Mexico.

In March and April this year, the SLPAs off the Mid-Atlantic states were strongly negative, again emphasizing the idea of fewer storms. The analog years that had negative SLPAs in this area were 1952, 1958, 1996, and 2001, all having no greater than three named storms or one hurricane. Another prominent correlation is with the QBO. Based on 55-year statistics, any given season with a westerly QBO has an 88 percent of having a Gulf of Mexico major hurricane, whereas the chance is only 36.7 percent during an easterly QBO. Sure enough, only one of our analog years, 1960, had a Gulf of Mexico major hurricane, and it also had positive SLPAs off the Mid-Atlantic coastline in March and April. Based on all of this information, only two to three named storms, one hurricane, and no major hurricanes are forecasted in the Gulf of Mexico this season.

X. Local Landfall Data

The theory of being able to forecast which areas of coastline will be directly affected by tropical cyclones months in advance is and should be the long-term goal of seasonal forecasting. In order for such predictions to progress, its boundaries must be tested. Long range forecasting also becomes more accurate with an increase in experience. Therefore, experimental landfall forecasts will be included in IWIC’s seasonal forecast for a third year. Many researchers argue that landfall probabilities cannot be given with accuracy since the synoptic pattern is responsible for the steering of tropical cyclones. However, we argue that synoptic trends during spring along with climatological statistics regarding the trends can result in accurate landfall forecasting. Some of these correlations have worked in the past two years, whereas other have not. This year, we are investigating some new methods, and incorperating the ones that have shown skill in the past two seasons.

Texas and northern Mexico

The western Gulf coast was hit by at least one tropical system in all of our analog years except 1952. Upon further examination of 1952 in comparison to the other analog years, it was noticed that it is our only year that had above average spring rainfall in Texas. The rest of the analog years more or less saw dryness in Texas and other South-central portions of the United States. Since less precipitation is usually a product of stronger high pressure, and stronger high pressure prevents storms from curving poleward, this correlation is fairly logical. A stronger ridge over Texas will tend to steer tropical cyclones in the Gulf of Mexico towards the west.

This spring, precipitation over Texas and the southern Plains has been below normal. Therefore, 2005 is not in the same boat as 1952. Some of our analog years with similar dryness, such as 1989 and 2003, had three named storms, two being hurricanes, hit the western Gulf coast. However, these years also saw more overall activity in the Gulf of Mexico, which should not be the case this year. Taking this and the extent of the dryness into account, the best analog years for this landfall region are 1958, 1960, and 1996. One to two named storms, one possibly being a minimal hurricane, are forecasted to hit the Texas or northern Mexico coastline this season.

Louisiana

Louisiana was hit by only one named storm out of the seven selected analog years. The best three Gulf of Mexico analog years, 1958, 1996, and 2001, witnessed no landfalls, with the exception of Subtropical Storm Allison. Allison was not included within the sample due to the fact that it already made landfall in southeast Texas, and remarkably managed to re-enter the Gulf of Mexico after losing some tropical characteristics. The likelihood of such an event taking shape this season is considered low. The forecasted 2005 synoptic pattern does not favor a tropical cyclone moving northward towards the central Gulf coast without recurving prior to landfall. The Bermuda High positioned off the United States east coast interacting with a weakness over the Mississippi Valley is more likely to steer any central or eastern Gulf of Mexico storm to towards Florida. Any storm in the western Gulf of Mexico, on the other hand, will likely make landfall further west under the influence of a prominent ridge in the United States central Plains. Therefore, Louisiana should avoid being hit by any named storms this year.

Mississippi through Florida Panhandle

This region was hit by a total of three named storms and one hurricane out of the selected analog years. The only hurricane to make landfall was Ethel in 1960, and 1960 does not seem to fit the overall pattern that has been surmised. If the top three Gulf of Mexico analog years are used, the panhandle was hit by one named storm two out of three years. As explained in the previous section, a longwave trough over the southeast and northern Gulf of Mexico would likely recurve any central or eastern Gulf of Mexico tropical cyclone towards Florida. It is hence interesting to note that every analog storm originated in either the central or eastern Gulf of Mexico. 1960 is the only analog year that supports the possibility of a big hurricane threatening the western side of Florida from the Caribbean Sea or Bahaman area, but that was also a favored season for high Gulf of Mexico activity, unlike this year. If this area does witness tropical cyclone activity, then no more than one tropical storm landfall is supported by our statistics.

Western Florida Peninsula

After witnessing borderline Category Five Hurricane Charley in 2004, it will be interesting to see how the 2005 hurricane season pans out for the Gulf Coast side of the Florida peninsula. There has been a lot of hype about the possibility of this year setting up in a similar fashion as did the 2004 season. The expected positioning of the main steering parameters is enough to express at least some concern. As you will read under the section referring to Cuba, a track similar to that of Hurricane Michelle in 2001 cannot be ruled out this season. Remember, only a couple hundred mile variation to the north could have meant disaster for southern Florida. Luckily, the trough over the United States east coast was enough to steer Michelle east of the peninsula.

There are several examples in our analog years of tropical cyclones originating in the northwest Caribbean Sea. Nearly all of these cyclones turned northeast, but they passed just to the south of the Florida Keys and hit central and western Cuba instead. On the other hand, while Hurricane Donna in 1960 was not exactly a Caribbean Sea hurricane, it did not curve until 80 degrees west, which is right over the Florida peninsula. Such a path can never be ruled out, but none of the remaining data suggests that this type of track is likely. Finally, we expect the mean positioning of the United States east coast trough to be far enough south to recurve storms like Charley before entering the southeast Gulf of Mexico.

Any named storm that develops in the central or eastern Gulf of Mexico very well could curve to the east or northeast, however. Fortunately, most Gulf originating storms struggle to begin rapid deepening cycles, and any Florida hit from the west would likely be from a tropical storm. The less activity in the Gulf of Mexico in the first place would argue against not only the region being a target to multiple hits, but also anything intense. One tropical storm is forecast to hit the western side of the Florida peninsula this season.

Eastern Florida Peninsula and Keys

The eastern Floridian coastline was hit hard by two significant hurricanes last season, Frances and Jeanne. From a climatological point of view, this region does not look to be a target this year. The only tropical cyclone in our analog years that hit Florida from the east was major Hurricane Donna. However, Donna appears to be an outlier, and the expected synoptic pattern does not support such a track. Further reasoning for less than average probabilities for this region is simply the fact that the setup may not allow hurricanes to enter the Gulf of Mexico. Nine out of the 11 hurricanes that have hit the eastern Florida coast since 1950 were in years with positive SLPAs off the Mid-Atlantic in March to April. Ten of the same 11 hurricanes, 90.9 percent, were also in years when the preceding winter NAO was negative. Both of these favor a more westward displaced Bermuda High, and both are not the case in 2005. Thus, once a tropical cyclone is in the Bahamas, a more northerly track out to sea or further up coast is more likely this season. No landfalls are anticipated along the eastern Florida peninsula, though there will probably be at least one close call. This expectation might as well be viewed as a hit to err on the side of caution, because only a small break in the overall progged pattern could result in another troublesome season for Florida.

It should also be mentioned that the small section of Georgia’s coastline just above Florida has not been directly hit by a hurricane in over 100 years. This leaves us with a limited climatological sample of lanfalls for the region, and thus it is too difficult to provide landfall forecasts for Georgia. However, just because it has not been hit in a long time does not mean it will never be hit again.

The Carolinas

Early indicators suggest that the Carolinas will be extremely susceptible to hurricane landfalls this season. As noted in the pattern discussion, six out of seven analog years featured at least one hurricane landfall, the outlier being 2001. Five out of the same seven analog years had abnormally wet conditions in and around the Carolinas; the two exceptions were 1960 and 2001. The flaws found in 1960 have already been outlined in different sections of this seasonal forecast, so our attention is drawn to 2001. That year, the Carolinas were drier than average. In addition, upper level ridging along the Eastern Seaboard was present more than any other year. The remaining five analog years had already shown indications of a longwave trough by April to May along the eastern states. Greater trough frequency became even more prevalent during their respective hurricane seasons.

Unfortunately, similarities between 2005 and the analog years with Carolina hurricane hits have become apparent. A detailed description of this year’s pattern has already been explained under prior sections, but the following points are highly crucial for this region in particular. This year, two abnormally positive areas of high pressure in the mid-levels have developed: one over the Iberian Peninsula and the other just south of the Canadian Maritimes. Both anomalies could have been predicted based upon the five Carolina landfall analog years. Second, there has been a minor weakness between these positive anomalies near 30 degrees west and 50 degrees north, a feature also noted in the exact same area within the landfall analog years’ geopotential height average. Finally, a weakness in the pattern has been in place over the eastern United states the majority of the spring. The positioning of the trough is the most important key. All of the landfall analog years had an eastern United States trough in one form or another.

The evolution towards the synoptic pattern required for a busy Carolinas season is already underway. Further evidence is seen with the strong ATC combined and the lack of an El Nino. One or two named storms, with one being a significant hurricane, are expected to hit the Carolinas this season. There is a chance that these numbers may be slightly conservative. 1996, which had three named storm and two hurricane landfalls, including Fran, was one of the five landfall analog years.

Mid-Atlantic States and New England

The progressive trough over the eastern United States combined with a stronger than normal subtropical ridge to the east may allow a few recurving tropical cyclones to come rather close to this portion of the coast. However, the ridge does not appear to be strong enough to guide any tropical systems due north into the northeast or New England states. Concerns for an in-situ hurricane similar to Belle or Bob are low this year, as these types of systems are more likely to occur in years with an El Nino or weak ATC, both which enhance dynamics needed to develop tropical cyclones from lingering fronts. Therefore, it appears that if any tropical cyclone is going to impact the United States east coast from Virginia to Maine, it would likely come from a recurving system that already made landfall in the Carolinas.

Canadian Maritimes

There is a good chance that the Canadian Maritimes will feel the effects from at least one tropical cyclone this season. 1952 and 1960 were the only two analog seasons in which no tropical cyclone made it as far north as the Canadian Maritimes, and both had close calls. This inference fits with the forecasted track pattern of more recurvatures but some getting close and hitting the United States east coast. Many storms that recurve just east of the United States are guided into Canada before becoming extratropical. Some tropical cyclones that form in the subtropical latitudes can move into Canada as well, such as Karen and Juan, interestingly both in two different analog years. Although a Canadian hurricane to the magnitude of Juan is extremely rare, the Canadian Maritimes are likely to experience one named storm with tropical characteristics this year.

Bahamas

The Bahamas have the potential to be hit from two different regions this season. First, a few tropical cyclones are expected to be directed towards the east coast of the United States, particularly the Carolinas. Such tracks often place the Bahamas under the first bull’s-eye depending on how much longitude is gained prior to the beginning of recurvature. Second, the potential threat of recurving hurricanes from the southwest Caribbean Sea in the latter half of the season must also be taken into account. With this in mind, the Bahamas have a good chance of experiencing two hurricanes this year, one possibly being major. The Bahamas are often overlooked at as a landfall region, but in 2005, the islands certainly stand out as one of the main target areas.

Cuba

Out of the seven selected analog years, Cuba was hit by a total of six named storms, four hurricanes, and three intense hurricanes. The island was not directly hit by any tropical cyclones in 1960, 1989, and 2003. In order to obtain more consistent statistics, each analog year had to be broken down. While no significant problems could be found with 1960, it is interesting to note that Havana barely escaped the inner core of major Hurricane Donna, which passed just to the north and hit southern Florida. Second, the two remaining years that did not have any landfalls, 1989 and 2003, experienced more mid to upper level ridging over the northwest Caribbean Sea and Florida Straits and less troughing over the southeast United States than other analog years. An even share of tropical cyclone activity was located in the Gulf of Mexico, and a more persistent trough allowed most of the Mean Development Region originating systems to pass to the north.

If 2005’s spring synoptic pattern is any indication, and our research has led us to that conclusion, then 1952, 1958, 1996, and 2001 are the favored analog seasons for this region in particular. These years suggest that a mid to upper level trough will generally hang around the Eastern Seaboard for the peak of the hurricane season. Meanwhile, the favored positioning of the subtropical ridge is expected to be somewhere near 30 degrees north and 55 degrees west. The positioning of these two parameters are highly crucial. If the overall pattern does setup as forecast, then a decent southwest flow stretching from the northwest Caribbean Sea northeastward into the Bahamas will develop. Such a pattern would be a dangeroues one for Cuba, especially towards the second half of the season. All four landfalls occurred from hurricanes that originated in the southwest Caribbean Sea in October, a region that is expected to be highly favorable this season due to the lack of an El Nino and a strong ATC. Two out of those four systems were major hurricanes. One or two named storms, and one major hurricane is forecast to directly hit the island of Cuba.

Hispaniola, Puerto Rico, and Lesser Antilles

Hispaniola, Puerto Rico, and the Lesser Antilles are among the more vulnerable areas in any given hurricane season, and climatological evidence tends to point that they are especially so this year. However, there is great disparity in how hard the region was hit in our analog years. 1960 and 1989 had major Hurricanes Donna and Hugo respectively. 1958 had Hurricane Ella hit Hispaniola, and 1996 also saw Bertha and Hortense. The rest of the analog years, on the other hand, only saw tropical storm hits. The high amount of named storms we expect developing in the Mean Development Region, more so than many of our analog years due to the stronger ATC, rationally increases the chance of a significant hit in this area. More intense ridging on the east side of the strong trough along the United States east coast suggests a greater risk to the eastern Caribbean islands as well. At least two named storms should pass through these islands, with at least one being a hurricane. A major hurricane hit is a decent possibility taking the above into account.

Eastern Yucatan Peninsula and Central America

This large region was completely spared a hit during the monstrous 2004 season. In 2005, the threat of a storm tracking through the entire Caribbean Sea and into Central America is fairly low, though one in July or August cannot be ruled out. Any western Caribbean Sea storms that develop in October or November will be prone to move poleward due to a stronger trough, putting Cuba at a greater risk during that time of the season. Therefore, virtually the only way Central America or the Eastern Yucatan Peninsula will be hit this year is if a storm develops in the western Caribbean Sea during the early or middle season. Tropical cyclones in the area in July through September will be more likely to be pushed westward into this region, with the dominion of the United States east coast trough not setting in so far south until October. Considering that the western Caribbean Sea should be favorable for such storm development during the season, this type of storm is possible. One named storm, perhaps a hurricane, is forecasted to hit the Eastern Yucatan Peninsula and Central America.

XII: Monthly Breakdown

The Atlantic Basin hurricane season officially spans six months, beginning on June 1 and ending on November 30. Unlike landfall and regional forecasting, it is very hard to venture out and predict tropical cyclone activity for each month or pair of months by observing the recent patterns alone. Therefore, we looked primarily at climatology and data from analog years for this section of the forecast.

June and July

Generally speaking, the first two months of the Atlantic Basin hurricane season are relatively quiet. On average, one to two named storms form in these months combined. The amount of activity that occurs in June and July does not have any bearing on how active the remaining four months or the season altogether will be. In 1997, the tally stood at five named storms by August, and yet only three others developed after that. On the contrary, the first named storm in 2004 did not form until August, and it turned out to be one of the most intense seasons on record.

Regardless, climatological evidence points towards above average activity during June and July this season. Every single one of our analog years had its first named storm in June or, in the case of 1952, earlier. This is consistent with our 55-year data showing that years with an easterly QBO have a 73 percent chance of a June or pre-June storm, versus a 48 percent chance in westerly QBO years. While the statistics raise eyebrows, it is difficult to come up with a logical reason for this relationship, as is often the case when the QBO is involved. The QBO exhibits a similar, though less robust, correlation with July activity. Years with a neutral ENSO similarly tend to have more activity during June and July than when either La Nina or El Nino conditions are present. A possible explanation for this is that in an El Nino year, other factors aside, the late spring and early summer pattern tend to feature an abnormally strong and low jet stream. The strong zonal flow associated with this is not favorable for early tropical cyclone development. In a La Nina summer, there are usually much less frontal features dipping down into the tropics in the first place. This is a problem as well, as many early season storms are spawned in part by remnant frontal boundaries. The most conducive ENSO scenario is neutral. Fronts are not completely hindered, but at the same time the longwave flow is still amplified enough to allow for cyclogenisis in the tropics off remnant frontal tail-ends. What may be an even more favorable setup is not only a neutral ENSO during the summer, but one succeeding a previous warm ENSO winter. This was the case in three strong ATC seasons: 1966, 1995, and 2003, which featured five, five, and four named storms before August respectively.

This year, the QBO is easterly and the ENSO should stay primarily neutral. Furthermore, there was a weak El Nino this previous winter. All of this is statistically promising for above average levels of activity in June and July, and with a strong ATC, 2005 fits in the list of three years above. A named storm is forecasted to develop sometime in June. Two to three more are expected to form in July, with one or two of those likely being hurricanes.

August and September

Atlantic Basin tropical cyclone activity tends to experience a fairly sharp increase during the month of August, particularly after August 15. August and September are by far the most active months of the season, with the climatological peak of being in early to mid September. In almost all cases, an above average hurricane season equates to above average activity in these two months.

A hyperactive hurricane season is expected. Thus, an active combined August and September is logically probable. Upon investigating previous hurricane seasons, we noticed two separate groups in the years with high activity in these months. One group contains years that featured a general range of six to eight named storms in August and September, which is above normal, but not overly so. On the other hand, there are other years that had over ten named storms in the same timeframe, a rather explosive amount of systems for such a duration. This poses the question of exactly how active the peak two months will be this season. We further examined the eight years since 1950 with ten or more named storms and interestingly enough discovered that seven of them, 87.5 percent, had no more than one tropical storm prior to August. In fact, only one year, 1995, saw its first named storm before July 20. But the overwhelming majority of the seasons with extreme levels of systems in August and September got off to very slow starts. Although we cannot perfectly explain the outlier, the overall strong trend observed here does make sense. One of the main roles of a tropical cyclone is to transport heat from the tropics to the polar latitudes. More oceanic heat is still preserved by the time August arrives in years with little June and July activity. In those kinds of seasons, a higher number of storms are able to develop during August and September, provided the main atmospheric factors are favorable.

As we went into detail about in the above sub-section, an above average amount of tropical cyclone activity is expected before August. Assuming that is true, then it is unlikely that more than eight named storms will develop during the middle two months of the season. Considering that a lot of this activity will probably come from the Mean Development Region, a fairly high percentage of the tropical storms that form should strengthen into hurricanes. Major hurricane activity will no doubt occur, though with QBO being in its easterly phase, we can expect it to be suppressed at least to some degree. Six to eight named storms, four to five hurricanes, and three major hurricanes are forecasted for August and September, with September being the most active of the two.

October and November

When October approaches, a noticeable decline in Atlantic Basin tropical cyclone activity is observed. On average, there are two to three named storms in October and November, which is far less than what is typically the case in August and September but slightly more than the first two months. However, in uncommon cases, there can be more activity during these months than around the peak, such as what was observed in 2001. On the other hand, even the most active seasons like 2004 sometimes almost completely shut down after September.

Our research indicates an above average level of storms during the latter portion of the season. A simple look at our analog years was not enough to come up with a logical prediction due to the surprisingly wide range of tropical cyclone frequency in October and November. The first trend that was noticed upon examining all of the most recent 55 seasons was that the stronger the ATC, the more activity observed in the last two months. This is not surprising considering a strong ATC is favorable for Atlantic Basin activity as a whole. The relation with ENSO is a bit more interesting. When a moderate or strong El Nino is in place, activity during the last two months is almost always reduced below average due to the stronger subtropical jet stream and associated westerly shear over the basin. Conversely, and to no amazement, more intense tropical cyclones are observed late in the season when a La Nina is present. However, it is found that seasons with neutral or even warm biased ENSO tend to have a higher amount of storms than what is seen in a La Nina, especially when coupled with a strong ATC. The most logical reason for this is similar to what was outlined in the June to July sub-section. While a La Nina favors the stronger low-latitude systems, there are generally fewer cut-off lows in the subtropics, which often transfer to warm-core tropical cyclones in the late season.

Since a neutral ENSO and a continuation of the warm ATC are both in the forecast, we expect four to five named storms to form after September, with two to three of those strengthening into hurricanes. Whether one of those is a major hurricane or not depends largely on how warm the ATC is and any ENSO bias. It is tough to tell for sure whether the neutral ENSO will lean more towards warmer or cooler SSTAs by autumn, but a very strong ATC is almost a certainty. Furthermore, 71 percent of all the Caribbean Sea major hurricanes after September occurred when the March through April SLPAs off the Mid-Atlantic states were negative, as was the case this year. Based on this, the 2005 season has a decent shot of having a Caribbean Sea major hurricane during October and November.

XIII: Summary and Conclusion

The recent upswing in tropical cyclone activity in the Atlantic Basin is showing no signs of ending. A strong ATC combined with neutral ENSO conditions should allow the above normal trend in tropical cyclogenesis to continue into the 2005 season. There are some notable characteristics that stand out in our preseason data. There will be a higher than average amount of hurricanes originating in the Mean Development Region, but this year the synoptic steering pattern favors the majority of them recurving at sea. One or two should impact the eastern Caribbean islands. At least one is likely to make it to the United States as a significant hurricane, most likely the Carolinas rather than Florida or anywhere along the Gulf coast. The Gulf of Mexico itself should be devoid of many storm originations as well, therefore being more tranquil than previous years. The first and final thirds of the season are forecasted to be more active than usual, but the peak will also almost surely be less intense than 2004. The western Caribbean Sea is a region to watch in particular during the early and latter portions of the season. During October or November, Cuba faces a strong chance of having a major hurricane from this region, provided ENSO does not become too warm-biased. Finally, we present our forecasted number of systems below.

IWIC 2005 Atlantic Basin Hurricane Season Forecast

Parameter 2005 Forecast Long Term Average
Named Storms 15 10
Hurricanes 8 6
Major Hurricanes 4 2

Regardless of our exact expectations for 2005, one in a hurricane prone area should always be prepared for a landfall well in advance. Even if for some reason 2005 turns out to be inactive, it only takes one intense landfalling hurricane to make the season a devastating one. A well-known example of this is the 1992 hurricane season. This was a well below average year by almost all activity measures, yet it was the year of Category Five Hurricane Andrew, which slammed into southern Florida and resulted in over 30 billion dollars of damage.

This seasonal forecast will not be updated during the season, though smaller updates will be posted on our site if necessary. We hope to write and publish a verification of our predictions contained in this forecast when the hurricane season is finished. A preliminary outlook for the 2006 Atlantic Basin hurricane season may also be posted sometime during November.

IWIC Experimental 2006 Atlantic Basin Hurricane Season Forecast

I. Introduction

This is the fourth Atlantic hurricane season forecast issued by the Independent Weather Information Center. Although we have had some successes in the past three years, our 2005 landfall forecasts did not verify well. The expectation of reduced activity in the Gulf of Mexico could not have been further off. As tempting as it was to accept the 2005 season as a rare anomaly and return to traditional forecast methodology in 2006, we could not do that. Upon an intense post-review, we now believe several of our hypothesized correlations were flawed due to misrepresentative statistics. It would be completely imprudent to use these same correlations again this year after showing no skill whatsoever in 2005.

With this in mind, we have abandoned many of the techniques used in years past. However, those that have read our seasonal forecasts over the years should not conclude that we are starting from scratch altogether. The methods that have consistently worked in the past are still being applied. Yet, we are introducing some new, promising methods based on data and research obtained from November through May. The primary parameters that are known to affect the frequency and steering of tropical cyclones in the Atlantic Basin have been closely analyzed throughout the offseason. A thorough explanation and forecast of these factors are outlined. In addition, up to 56 years of climatological evidence have been included to coincide with the anticipated 2006 summer pattern over the northern hemisphere. All of the aforementioned data has been utilized to not only forecast seasonal tropical cyclone activity, but also month-by-month activity, regional activity, and landfall probabilities.

There are a few verificational guidelines. First, any tropical cyclone development beyond November 30th will not be included within the verification of this seasonal forecast. Second, only forecast totals of tropical storm, hurricane, and major hurricane activity are provided in our regional and landfall sections. Tropical depressions that don’t strengthen further are not included in any of our forecasts. Third, a tropical depression that develops in a particular region and moves into another region before becoming a classified tropical storm counts as a tropical storm development in the region it officialy becomes a storm in. Fourth, any tropical cyclones that hit the western side of the Florida peninsula and make it into the Atlantic Ocean are not considered a hit to the eastern side and vice versa. The same goes for the Yucatan Peninsula. Additionally, any storm that hits the Gulf Coast and attempts to regenerate over the East Coast during recurvature does not count as an East Coast landfall.

Although no long-term forecast has ever been absolute, we certainly strive for accuracy each and every year. Also keep in mind that this forecast is experimental and unofficial, and therefore we are not liable for one’s actions based upon the information being presented. Please read our disclaimer.

II. El Nino Southern Oscillation

The El Nino Southern Oscillation, commonly referred to as ENSO, is an important parameter concerning Atlantic Basin tropical cyclogenesis. ENSO is most notably characterized by significant variations in sea surface temperature anomalies, or SSTAs, in the equatorial Pacific Ocean, though alterations in sea level pressure, trade winds, and convection are also observed. Warm SSTAs are associated with El Nino episodes, whereas La Nina episodes correspond with cool SSTAs. If SSTAs are neither warm nor cool, ENSO is considered neutral.

Once an El Nino event takes hold, strong upper level westerly winds dominate the low latitudes of the Atlantic Basin. As a result, hurricane development from tropical waves and disturbances along the intertropical convergence zone is typically suppressed. In the mid-latitudes, a higher frequency of upper level troughs and other dynamics that support the development of cutoff lows is typical. High latitude tropical and subtropical activity is thus increased during El Nino events. The reverse is true for La Nina. There is only a small difference between the number of named storms in an El Nino versus a La Nina, but far more hurricanes and intense hurricanes are observed in a La Nina or even neutral ENSO conditions than in an El Nino event.

Current Status of ENSO

During the last two months of 2005, the neutral ENSO began showing signs of transitioning to a La Nina. SSTAs across the equatorial Pacific Ocean cooled to values below -0.5 degrees Celsius, and the global pattern reflected this change during the Northern Hemisphere winter. As such, La Nina was officially declared in January. However, this La Nina remained generally weak and did not intensify much further after classification. In March of this year, the SSTAs began slowly moderating above the La Nina threshold. This trend has continued through May, with values currently leaning slightly above average in all ENSO regions except 1.2, just off Peru. Furthermore, there has been a significant change in the depth temperature anomalies, or DTAs, across the equatorial Pacific Ocean. The strong cool pool that extended down to 200 meters below the surface in tandem with the weak La Nina event has almost completely disappeared. A static, small warm pool has been present under the western equatorial Pacific Ocean for several months. Such a warm pool is fairly typical in a La Nina or neutral ENSO, and can expand and progress if a Kelvin Wave passes over the area. When this happens, it is common for an El Nino to initiate. However, there have been no observed Kelvin Waves yet this year, and thus it is no surprise that the pool has not shown signs of moving.

Another important aspect of the ENSO is the Southern Oscillation Index, or SOI. It is defined by sea level pressure differential between Tahiti and Darwin, Australia, with negative values corresponding to El Nino, and vice-versa. The SOI has remained largely positive over the past few months, coiniciding with the La Nina. While it is not as strongly positive as it was a few months ago, it is somewhat odd that the SOI has remained positive through this month, even though the ENSO is back to a neutral state. One responsible factor for the persistence is Cyclone Monica, which helped significantly lower pressures over Darwin during the last half of April. Since then, daily values have been hovering closer to normal, thus slowly drawing the more crucial 30-day and 90-day downward. With the cyclone season essentially over, and the overwhelming signs for a neutral or warming ENSO, it is expected the SOI will catch up to the equatorial Pacific SSTAs over the next month or sooner.

With the cyclone season essentially over, and the overwhelming signs for a neutral or warming ENSO, it is expected the SOI will catch up to the equatorial Pacific SSTAs over the next month or sooner.

Climatology

While climatology cannot always be trusted alone, it can be a helpful tool in long-range predictions of the ENSO. For climatological research we use the Multivariate ENSO Index instead of just SSTAs, as it also accounts the SOI, equatorial convection, and other global conditions that help determine ENSO. The MEI this past winter, from December to March, hovered around -0.450, plus or minus about 0.100. Upon examining the MEI over the past 56 years, we found 14 years that best matched the MEI this winter: 1957, 1960, 1961, 1965, 1967, 1968, 1972, 1982, 1984, 1985, 1986, 1996, 1997, and 2001. Six of these years saw the development of an El Nino in the summer, with one other year producing a very late fall El Nino. True La Nina conditions did not persist through the summer in any of the years, though a La Nina did rebound in three years, with others maintaining a weak cool bias. Clearly, climatology does not offer much help this year, except for eliminating an already-unlikely prolonged La Nina. If one takes the spring MEI values into consideration, which have so far not decreased much since the winter, the two best years out of this sample are 1985 and 1996. Interestingly, both never ventured away from cool bias ENSO conditions for the rest of the year. However, the equatorial Pacific Ocean SSTAs in 1985 were much cooler during the spring than this year, and a little cooler in 1996. Considering the faintly positive SSTAs this month, there is reasonable concern that the MEI will fail to stay negative through the summer, unlike those two years.

ENSO Prediction Models

Coupled and statistical ENSO models have been in use for several years to try to accurately predict the evolution of ENSO up to eight months in advance. Each individual model has a bias to one extent or another, and at certain times of the year. Therefore, it is better to look at the model consensus as a whole, and more importantly, the model consensus trend. This spring, the average of all the models combined is a continued slow warming over the summer, leading towards a possible weak El Nino by the end of fall. Some, such as the POAMA, were recently forecasting a substantial El Nino to develop over the summer. However, the POAMA now forecasts neutral or slightly cool bias ENSO conditions during the hurricane season. Ironically, several other models have trended warmer over the past few months. The CLIPER, a relatively good statistical model, is currently forecasting a weak El Nino during the hurricane season. As can be seen in the chart of selected models below, the majority favor neutral conditions during the last part of 2006.

ENSO Models September 2006 December 2006
POAMA Neutral Neutral
CPC Neutral Neutral
ECMWF Neutral Not Available
UKMO Neutral Not Available
LDEO Neutral Neutral
NCEP Neutral Neutral
NOAA LINEAR INVERSE Neutral Neutral
SCRIPPS/MPI Neutral Neutral
NSIPP/NASA Warm Warm
JMA Neutral Not Available
CLIPER Warm Warm
SSES Neutral Not Available

2006 Summer ENSO Forecast

The short-lived La Nina that ruled the past Northern Hemisphere winter is just about gone. As aforementioned, SSTAs have warmed in all ENSO regions of the equatorial Pacific Ocean over the past few months. The SOI has stayed positive with help from Cyclone Monica but is now slowly declining away from La Nina values. Additionally, the DTAs have a much more neutral appearance, with the large cool pool gone. MEI climatology for both winter and spring suggest cool-biased conditions, though with this year’s SSTAs a bit warmer, a notch higher in status appears likely. Finally, it is worth noting that the combined best five global predictors for forecasting ENSO a half year to year in advance, courtesy of Seseske 2004, suggest a neutral ENSO. Considering all of this, neutral to slightly warm conditions are expected over the summer. This is in line with most of the statistical and dynamical ENSO models. Later in the year, it is very possible that weak El Nino conditions will emerge. However, it generally takes a moderate El Nino to have a noticeable negative impact on the total amount of Atlantic tropical cyclone activity. In fact, some of the most active hurricane seasons in recorded history were during periods when ENSO was in a neutral state. 2005 is one of those seasons. The seasonal ENSO this year will overall neither help nor inhibit tropical cyclone formation. Therefore, the remaining factors known to influence Atlantic hurricane activity will carry more weight.

III. Atlantic Thermohaline Circulation

The Atlantic Thermohaline Circulation, or ATC, is a density-driven circulation in the Atlantic Basin that undergoes cycles on decadal timescales. When the ATC is in its warm or strong cycle, hurricane activity is increased. During the strong cycle of the ATC, the most notable consequence is warmer SSTAs across the tropical Atlantic Basin, which provides more energy for a tropical storm or hurricane to sustain deep convection. Additionally, lower vertical wind shear and sea level pressure anomalies, or SLPAs, are typically observed across the Atlantic Basin with a strong ATC. The exact opposite is true for the weak or cool phase of the ATC, which is inhibiting to tropical cyclone formation. Since 1995, the ATC has been in a strong cycle, which explains the significantly above average hurricane seasons that have occurred over the past 11 years. However, even during the ATC’s warm phase, it does occasionally fluctuate for several months. These small fluctuations are difficult to forecast in advance, but observing SSTAs in the Mean Development Region over a monthly period is an easy way to monitor such trends.

Since mid 2003, the SSTAs in the eastern Atlantic Basin have for the most part remained much warmer than average. Spring 2005 SSTA values in the Mean Development Region were record high, and although the SSTAs are not as high this year, they are nonetheless above average. Mean Development Region SSTAs during April averaged at 0.37 degrees Celsius above average and should be even higher this month. Given the mode of the ATC and warming trend observed in SSTAs, there is no apparent reason why a SSTA cooling would occur this summer. A continued warm ATC will act as a robust enhancing factor for tropical cyclone formation.

IV. Other Factors

Quasi-Biennial Oscillation

The Quasi-Biennial Oscillation, QBO, is a periodic variation in the direction of stratospheric winds across the deep tropics. The two phases, easterly and westerly, generally last from 12 to 16 months, with the easterly phase often having a slightly longer duration. Unlike ENSO, the QBO’s alternation between phases is timely, making it quite simple to forecast. The easterly phase of the QBO peaked last November, with a value of -29.55. Afterwards, the QBO rapidly rose and just recently this year has transitioned to the westerly phase. The QBO will continue to rise and peak later this year, with the next transition probably not occurring until sometime in early 2007. Traditionally, this is judged to be an enhancing status on Atlantic major hurricane activity, though the observed relationship has somewhat faded over the past few years.

North Atlantic Oscillation

The North Atlantic Oscillation, or NAO, is the fluctuation in 500 millibar heights in the northern Atlantic, primarily between western Europe, Iceland, Greenland, and the Canadian Maritimes. Although it plays an important role of the steering pattern across the Atlantic Basin, one problem that has prevented reliable techniques in forecasting the NAO months in advance is that it is extremely variable on a monthly and even weekly basis. It would be foolish to try to forecast its evolution through the rest of the year without the proper understanding that most have yet to acquire. However, our 56-year climatology does indicate that spring NAO values may have a lag influence on the conditions that set up during the hurricane season. The significance of the negative NAO that was in place this past March will be discussed in detail further down.

Pacific Decadal Oscillation

The Pacific Decadal Oscillation, or the PDO, is a multi-decadal pattern of high and low pressure systems in the northern Pacific Ocean, sometimes seen as a longer-term version of ENSO. However, unlike ENSO, the PDO index is calculated by spatially averaged monthly SSTAs over the northern portions of the Pacific Ocean, not the equatorial. In terms of its variability, the PDO is most similar to the ATC, given that it too fluxes on a multi-decadal basis between a cool and warm cycle. The cycle of the PDO switched to warm around 1977, and began showing signs of reverting back to the negative cool phase in the late 1990s. However, since late 2002, the PDO has been predominantly positive. Monthly values have been positive since last November, further suggesting that a full shift back to a cold-cycle has not yet occurred. Although the PDO is not known to exhibit impacts on Atlantic Basin tropical cyclone activity, it does correlate with geopotential heights over the United States and the adjacent Atlantic region. These heights in turn play a role in storm movement.

V. Activity By Region

The Atlantic Basin has been divided into separate regions so that the amount of tropical cyclone activity in each sector can be analyzed.

Mean Development Region

The Mean Development Region is the area between the Lesser Antilles and the western coast of Africa south of 20 degrees latitude. This is where tropical waves traverse and often develop into hurricanes either in the region itself, or later on in the Caribbean and western Atlantic Basin, hence its name. Although common logic dictates that the warmer SSTAs will result in increased activity in this region, the ingredients are not that simple. 2005 saw record warm SSTAs in the tropical Atlantic, but as active as the season was overall, the Mean Development Region escaped with only two weak named storms. This conundrum was a subject of study this offseason, and sure enough we discovered a potentially very important factor for Mean Development Region activity: the March NAO.

After analyzing data 56 years of data, it is our conclusion that when the March NAO is positive, activity in the Mean Development Region is enhanced. The opposite holds true when it is negative. For warm ATC seasons, the average number of named storms, hurricanes, and major hurricanes in the Mean Development Region when the March NAO is positive is 6.4, 3.7, and 1.4 respectively. Conversely, the average of the same parameters for negative March NAO seasons is 3.2, 2.0, and 0.4. The average number of named storms and hurricanes are doubled for positive NAO years, and the average number of major hurricanes is tripled. The difference in these values is rather noteworthy. Since the NAO in March 2006 was -1.3, it is expected that Mean Development Region tropical cyclone activity will be hindered this year.

To further solidify this hypothesis, it was found that every single year with a negative March NAO, including 2006, also had high geopotential heights over the tropical Atlantic or Cape-Verde area, and vice-versa for positive March NAO years. High heights in hurricane development zones do not correlate with high hurricane activity, but instead tend to increase atmospheric stability and higher SLPAs. These conditions just prior to the onset of hurricane season will suppress the intertropical convergence zone and help reduce convection in tropical waves until they reach the Caribbean Sea. The one parameter that might suggest a little more activity in this region than last year is the QBO. The westerly phase of the QBO has a faint but existent correlation with activity east of the Leeward Islands. Taking into account the QBO, ATC, ENSO, and most importantly March NAO, we expect about four named storms to originate in the Mean Development Region, with two or three becoming hurricanes, and one becoming a major hurricane.

Subtropical Atlantic Basin

The subtropical area of the Atlantic Basin is generally the place to look for frontal lows acquiring tropical cyclone status in years with El Nino or cool ATC conditions. Neither is the case this year, so frontal activity in the high latitudes will be restricted to at least some extent. Nonetheless, the combination of a warm ATC, neutral ENSO, and negative spring NAO is climatologically favorable. The resulted pattern in this type of setup involves increased trough activity across the western Atlantic Basin. The increased SSTAs in tandem with the ATC allow better dynamics for cut-off lows to develop, especially early and late in the season. Furthermore, there is always the possibility of a strong tropical wave not developing until it is in close to the Bahamas, a very common occurrence in last year’s devastating season. Finally, a couple of tropical cyclones are forecast to enter the western or central Atlantic from the Mean Development Region. Taking all of this into account, above normal tropical cyclone activity is expected in this region, with about four to five named storms developing in the area, two to three being hurricanes.

Caribbean Sea

We first begin with the eastern Caribbean Sea, often referred to as the dead zone of the tropical Atlantic Basin. Although tropical cyclones have passed through this part of the basin with no trouble, it is rare for a storm to actually develop here due to the summer and autumn presence of the Tropical Upper Tropospheric Trough, or TUTT. This feature induces strong southwesterly shear and thus usually keeps the region in check as far as development potential is concerned. It has been hypothesized that the easterly phase of the QBO during the summer and below normal SSTs could increase the effects of the TUTT on tropical cyclone activity. Since neither is the case this year, an inhibiting TUTT appears highly unlikely, and thus a favorable environment should prevail for storms entering the region. Having said that, there is a limit on the number of storms crossing the area considering the aforementioned problems with the Mean Development Region. Based on past warm ATC and negative NAO analogs including 1951, 1958, 1981, 2001, 2005, one to two named storms will probably enter or form close to the eastern Caribbean Sea this season.

In the western Caribbean Sea, the environment has supported many of the strongest Atlantic hurricanes on record, including last year’s Hurricane Wilma. This year, the western Caribbean Sea should be very favorable, largely owing to the above average SSTAs and lack of El Nino. Furthermore, the negative March NAO and resulted restraint on tropical wave development in the Mean Development Region only increases the likelihood of development in this region further west. The fact that at least one storm should move into this favorable area from the east spells major hurricane trouble. There is also concern for at least one system in this area late in the season, which will be discussed in further detail in the monthly breakdown section. Overall, three to four named storms should exist in this part of the Caribbean Sea, with one to two being major hurricanes.

Gulf of Mexico

Tropical cyclone activity in the Gulf of Mexico should be less active than the record amount seen last year, but far from absent. When neutral ENSO conditions prevail during the peak of hurricane season, as will be the case this year, one of the main dictating factors in Gulf of Mexico activity becomes the winter ENSO. An El Nino in the winter typically increases Gulf of Mexico tropical cyclones, whereas a La Nina or neutral winter often causes a reduction. Since the latter was the case this year, there will be a limit on Gulf of Mexico activity, particulary that of in-situ type. Moreover, two datasets of past warm ATC years were recorded: one consisting of years since 1950 and another for years since the recent uptrend, 1995. Both cases equally suggest the average number of named storms forming in the Gulf of Mexico is 45 percent higher when an El Nino is present in the preceding winter. The average number of storms in warm ATC years following Neutral/La Nina winters is approximately two. There is nothing to suggest that Gulf in 2006 will be more active than these sampled years, thus approximately two named storms are forecast to develop in the Gulf of Mexico. Furthermore, the springtime 850mb weather pattern would suggest most or all of these named storms that do form in the Gulf of Mexico would do so in the central or western Gulf, west of 88 degrees longitude.

Having said that, one also has to take into account storms entering the Gulf of Mexico from either the Caribbean Sea or western Atlantic. It appears that most storms that develop in the western Atlantic will track poleward and away from the Gulf of Mexico, an idea we will elaborate on further down. That leaves us with potential tropical cyclones traversing the central and western Caribbean Sea threatening the southern Gulf. One or possibly two named storms are forecast to enter the southwest Gulf of Mexico from the Caribbean Sea this year. An additional one or two named storms emigrating the western Caribbean may recurve into the southeast Gulf. In summary, four to five named storms are forecast to intersect the Gulf of Mexico this season. A few of these storms may strengthen into minimal or moderate hurricanes, but the potential for one or more major hurricanes in the Gulf is low based on our methodology. The reasoning behind our Gulf forecasts are explained in much more detail in the landfall sections below.

VI. Local Landfall Data

The theory of being able to forecast which areas of coastline will be directly affected by tropical cyclones months in advance is and should be the long-term goal of seasonal forecasting. In order for such predictions to progress, its boundaries must be tested. Long range forecasting also becomes more accurate with an increase in experience. Last year did not fare so well, but in the spirit of trying until success, experimental landfall forecasts will be included in IWIC’s seasonal forecast for a fourth year. Many researchers insist that landfall probabilities cannot be given with accuracy since the synoptic pattern is responsible for the steering of tropical cyclones. However, we argue that analyzing the overall synoptic pattern during spring, in combination with analysis of factors known to affect Atlantic hurricane activity, can enhance the accuracy of seasonal landfall forecasting.

This year, we are investigating entirely new methods based primarily on the 500mb and 850mb geopotential heights across North America, Atlantic Basin, and adjacent regions. Geopotential heights refers to the potential energy per unit mass of a body as a result of the earth’s gravitational field. Generally, low geopotential heights usually correspond to low pressure and vice-versa.

Texas and northeast Mexico

The coastlines of Texas and eastern Mexico, the western portion of the Gulf coast, faces the risk of seeing several tropical cyclones in 2006. One source of storms will be from the western Gulf of Mexico itself. As mentioned above in the regional section, the springtime 850mb geopotential height pattern this year consists of a ovoid ridge that stretches across the whole Gulf of Mexico from Florida to Texas. The ridge is centered over and south of Mississippi and Louisiana, so it is thus imparting north-northwesterly flow across much of the western Gulf of Mexico. Since we are forecasting two named storms to develop in the central or western Gulf of Mexico this year, and this layer is most critical for weak storms, one can put the two together. Unless a storm forms extremely close to the Mexican coastline and has no option but to move inland as a weak system, the steering flow supports tropical cyclones in the western Gulf of Mexico to have a more poleward component in their motion. This increases the risk towards Texas as opposed to Mexico from in-situ weak storms.

Having said that, several “weak” storms that have hit Texas in the past are notorious for rapidly strengthening just prior landfall. It is difficult, if not impossible, for us to say with certainty whether such intensification will occur this year. However, we can say with ease that if Texas is hit by a significant storm, it will not strengthen into one until very close to landfall. This is because the 500mb pattern in the Gulf of Mexico is a bit different: it is simply dominated by a strong, circular ridge centered over the Texas-Louisiana border. Therefore, the flow is westward at the 500mb level in most of the Gulf of Mexico. If a major hurricane enters the western Gulf of Mexico, it would stay south of Texas and strike Mexico under this type of pattern. Such a storm is not out of the question, but the other option is that a tropical cyclone hits the Yucatan Peninsula and enters the Gulf of Mexico as a weak system. A weaker storm would get steered more towards Texas.

Around three named storms are forecasted to make landfall in eastern Mexico or Texas this year. Texas is slightly favored over Mexico simply because at least two of these storms will be steered by the 850mb heights while in the Gulf of Mexico. Given the warm SSTAs this year, it would not be surprising to see at least one of these storms to strengthen into a hurricane before landfall. In-situ major hurricanes in the western Gulf of Mexico, while not unheard of, are rare enough to not forecast, though it is always a possibility. Finally, the final landfall of another storm that we expect will come from the Caribbean Sea will be determined by how strong it is when it reaches the Gulf of Mexico.

Louisiana, Mississippi, Alabama, and Florida Panhandle

It is a significant understatement to say the coastline from Lousiana through the Big Bend of Florida was hard-hit last year. This region was forever changed from Hurricane Katrina, not to mention the barrage of three other hurricanes. I, Jason Moreland, am a witness of the destruction and heartache along the entire central Gulf Coast. As a native New Orleanian, my life has forever been changed by the effects of Hurricane Katrina. As anyone that has been devastated by a hurricane can tell you, it’s no fun losing your home and having to unexpectedly move across the southeast for eight months. We can only hope that mother nature spares the central Gulf Coast from additional landfalls in the near future. According to the Army Corpse of Engineers, it won’t be until July or August when New Orleans’ levee protection system is completely restored to pre-Katrina levels, not to mention if Category Five protection will ever be implemented. Additionally, Louisiana, Mississippi, and Alabama are still far from even completing the clearing of debris process. All in all, Katrina recovery will take several more years, not months, and even then some areas will never be the same. I can also report that many residents of the Gulf Coast have been irritated by the lacking national media coverage of the grueling road to recovery many have undertaken.

Subsequently, one of the leading questions heading into the 2006 hurricane season is whether a tropical cyclone is likely to threaten the central Gulf Coast. Our outlook is encouraging for those in this area. First, we analyzed seasons that followed neutral ENSO or weak La Nina winters and had near neutral ENSO conditions by August, September, and October. Second, we eliminated the seasons that did not have a springtime weather pattern similar to spring 2006. In spring 2006, the central Gulf Coast was dominated by a mid-level 500mb ridge and an 850mb ridge near the surface. Past spring patterns including a dominant central Gulf Coast ridge are 1953, 1955, 1967, 1974, 1985, and 2000. 1953 was an active year for the Florida panhandle. Two named storms and one hurricane struck this area. In 1955, southeast Louisiana was struck by two minimal tropical storms. The Gulf Coast got a break in 1967 with no landfalls. The 1974 hurricane season brought Category Four Hurricane Carmen into central Louisiana. In 1985, a total of four hurricanes struck the central Gulf Coast. The Gulf Coast got another break in 2000 when only one minimal tropical storm struck the Florida panhandle. So even though we narrowed it down to six analogs, there is still quite a differential.

In consequence, we broke down the analogs further. In 1953, the Gulf Coast ridge was strong enough to protect Louisiana, Mississippi, and Alabama from tropical cyclones. However, it was too far west and weak to protect the Florida panhandle. In contrast, the 2006 ridge is setting up directly over the central Gulf Coast, and it is much stronger than the ridge witnessed in 1953. In 1955, the 500mb mid level ridge was strong enough to protect the area from significant tropical cyclone landfalls. In contrast, the 850mb ridge was oriented in a manner that allowed weak, southeast Gulf storms to head toward southeast Louisiana, hence the two minor landfalls. In 2006, a strong ridge at both the 500mb and 850mb levels is forecast to shunt any threatening storms westward toward Texas or Mexico. The 1967 analog is probably the best one for the Gulf Coast 2006 season. The 1967 ridge was positioned a little north of where it is this year, but its intensity over the coastline makes up for the greater distance. No landfalls occurred that year. In 1974, the only tropical system that impacted the central Gulf Coast was Hurricane Carmen. That year, The strong 500mb ridge over the coast kept Carmen on a westerly path up until the time it rapidly weakened over the Yucatan Peninsula. At that point, Carmen became influenced by the 850mb steering flow, which was vastly different and was oriented to favor minimal tropical cyclone landfalls along the northern Gulf coast. Carmen did rapidly intensify as it inched closer to Louisiana, but it was too late to cause the storm to steer back to the west before landfall. This year, the 850mb ridge is expected to be more protective, thus any landfalling Yucatan tropical cyclone will likely remain on a west or west-northwest heading rather than turn north. In 1985, several hurricanes struck the area despite the strong ridging that was present. Even so, the steering pattern over thewestern and central Atlantic made it favorable for tropical cyclones to enter the southeast Gulf, and it turns out that those such storms later struck the Gulf Coast. This year, the pattern over the western Atlantic is not conducive for tropical cyclones entering the eastern Gulf from the direction of the Bahamas or Florida. The remaining two landfalling tropical cyclones in 1985, Danny and Juan, originated in the central Gulf and were steered straight into the Gulf Coast because the 850mb ridge was anchored closer to the East Coast rather than the northern Gulf, creating a low-level southeast flow. Again, the low-level steering pattern of 2006 is expected to keep minimal tropical cyclones south and west of the central Gulf Coast. Finally, the 2000 season delivered one tropical storm to Pensacola. The ridging over the panhandle is stronger this year.

In summary, little to no tropical cyclone activity is forecast along the central Gulf Coast in 2006. The Gulf Coast ridge is expected to previal through the peak of the season. Minimal tropical cyclone development near the coast is always possible, but none of our data suggests that such a scenario is likely this year. This forecast is similar to the one released in May 2005, but we have developed an entirely new landfall forecast methodology soley because of the unexpected central Gulf landfalls last year. Our new methodology has yet to be tested, and we have the utmost confidence in it. With that being said, remember this is an experimental and unofficial forecast product.

Western Florida Peninsula

Once again, landfall analogs were determined by listing all seasons that followed neutral ENSO or weak La Nina winters and had spring patterns similar to spring 2006. The most notable springtime features we looked for was a strong Gulf Coast ridge and troughing over the central and western Atlantic. Six analogs met this critera: 1953, 1955, 1967, 1974, 1985 and 2000. Much like the original central Gulf Coast analogs, the number of tropical cyclones affecting western Florida in the following years varied quite a lot.

In 1953, the Gulf side of the peninsula was struck by three minimal tropical storms. Two originated in the northwest Caribbean while one developed in the central Gulf. The level of ridging extending from the Gulf Coast ridge this year is quite similar to the level of ridging witnessed over the peninsula in 1953. The height fields may be a little stronger, but not enough to dismiss the threat of similar tropical cyclone landfalls along the peninsula this year. 1955 met basic analog criteria, but the core of the Gulf Coast ridge was partially anchored over the Florida panhandle, and that does not match 2006 as much as one would like. The panhandle-anchored ridge significantly lessened the potential for southest Gulf storms to recurve over the peninsula. It’s no wonder that no landfalls occured that year. 1967 is better but not by much. The 1967 Gulf Coast ridge was centered far enough away from Florida, but positive height fields over Jacksonville, Georgia, and the Carolinas were much greater in 1967 than 2006 thus far. Moreover, heights in the central/western Atlantic have been a lot lower this year in contrast to 1967. No landfalls occurred over the Gulf side of the peninsula in 1967, but less ridging over the southeast and lower heights over the western Atlantic may increase the likelihood of tropical cyclone recurvature over the peninsula this year. In 1974, a subtropical storm formed in the Gulf of Mexico and struck Florida just south of Tampa. The positive height fields extending from the Gulf Coast ridge resemble 2006 much like 1953. One interesting differential between 1953 and 1974 is the ovoid orientation of the height fields over Florida. The 1953 orientation of the fields were more southwest to northeast whereas they were more west to east in 1974. Thus, the orienation of the ridge in 1953 may have made western Florida more suscepitble to multiple recurving cyclone landfalls than in 1974, despite similar height anomaly values. In 1985, one tropical storm formed west of Sarasota and headed east into the peninsula. Much like 1953 and 1974, height fields over the Florida peninsula in 1985 are very similar to those in 2006. 2000 is one of the worst analogs out of the selection, but the overall pattern this year is still close enought to provide clues. The core ridging in 2000 was centered over southeast Canada and the Great Lakes, but they extended well into the central Gulf of Mexico. However, had the the high been centered closer to the Gulf, the two tropical cyclones that hit the panhandle probably would have struck the western side of the Florida peninsula instead.

In conclusion, one to two named storms are forecast to develop or move out of the northwest Caribbean and southeast Gulf of Mexico and eventually recurve into the western side of the Florida peninsula. The threat of one or both of these named storms strengthening into minimal or moderate hurricanes prior to landfall cannot be ruled out.

Eastern Florida Peninsula and Keys

Interestingly, eastern Florida landfalls are not very common in years following neutral or La Nina ENSO during the winter. Only six out of 26 years with such winter ENSO conditions and neutral ENSO conditions during the peak of the respective seasons had eastern Florida landfalls. These six years are as follows: 1950, 1960, 1979, 1981, 1984, 1985. First off, the only year on this list that had a negative March NAO similar to this year is 1981, and one could even argue that the Florida tropical storm landfall was more of a hit on the southwest. Moreover, none of these years equally matched the strength of spring 2006’s Gulf ridge or central Atlantic trough. Aside from 1981, which again had a disputable and weak east Florida landfall, all of these years featured early ridging in the western Atlantic during the spring, which enabled storms east of Florida to feel the influence of easterly flow and track towards the state. Such a steering flow is not likely given the incresed troughing in the subtropical Atlantic this spring. A few of the seasons that had no landfalls matched this 2006 springtime pattern much better than those with landfalls. Based on this information, we do not expect any landfalls along the Atlantic side of the Florida peninsula this season.

Georgia and the Carolinas

The common theory these days is that if the Gulf of Mexico has an active season, which was the case in 2005, the following season will have more activity along the East Coast. That is not always the case, however. If multi-annual trends were that simple to follow, then a lot of government and independent agencies probably would have solved the seasonal landfall forecast problem by now. Our newly developed methodology this year yields little threat of tropical cyclone landfalls between Georgia and North Carolina this season, much like a good portion of the U.S. Gulf Coast.

First off, the negative March NAO translates into fewer storms developing in the Mean Development Region, the birth place of many Carolina-bound hurricanes. This alone puts a significant damper on the major hurricane threat for the Carolinas this year. To be fair, a majority of years with neutral ENSO or weak La Nina winters and neutral ENSO summers had landfalls in this area. Nevertheless, only one of these landfall years, 1952, had a pattern resembling the one we are expecting to prevail through 2006. There are even problems with using 1952 as an East Coast analog. The steering pattern in 1952 was more susceptible to fluctuating or shifting, and even when the pattern best matched 2006, the central Atlantic trough did not extend far enough into the southwest Atlantic. This year, we anticipate stronger troughing in the central and western Atlantic, thus eliminating the threat of long tracking storms slamming into the Carolinas or Georgia. Several storms are forecast to recurve out to sea north of Hispaniola and Puerto Rico. Tropical cyclones that develop close to the East Coast and hit land like the ones observed in 1953 and 1961 are less likely this year. Any storms that do develop over the eastern Bahamas or southwest Atlantic will be more prone to recurvature rather than riding up the East Coast. The ridging over the Gulf Coast only extends as far east as the Florida peninsula, and troughing has been prominent across much of the southwest Atlantic. One of the basic analogs that did not have any Georgia or Carolina landfalls was 2000. 2000 carries more weight than 1952 because Gulf Coast ridging and central Atlantic troughing was present, whereas both features had difficulty coinciding with each other in 1952. Due to North Carolina’s natural, geographical vulnerability, a brush from a storm forming immediately offshore can never be ruled out, but no tropical cyclones are forecast to slam straight into the Carolinas or Georgia this season.

Mid-Atlantic States and New England

There is not much more to add from what has already been stated in the Georgia and Carolinas landfall section. Since 1950, there were no direct hits from tropical Atlantic-originating storms in years with negative NAO during March except for 1971 and 1954. The pattern in 1971 featured a longwave trough situated over the East Coast with ridging to the east, so it is no wonder a storm made it to New England this year. If one counts all direct hits on New England, regardless of origin, no storms forming in the western Atlantic hit the area in a neutral season ENSO and a cool ENSO in the preceding winter. It also must be noted that, barring 1954, the only times the Mid-Atlantic States and New England were affected by tropical cyclones were when storms had begun recurving after striking the Carolinas or Gulf Coast. The setup with ridging over the Gulf Coast and troughing over the central Atlantic should significantly lower the probabilities of central Gulf Coast or East Coast hits this year, thus we do not anticipate any recurving storms of that nature this season.

Other forecast agencies have pointed out 1954 as an analog for the 2006 season, respectfully. The 1954 season included two moderate hurricanes landfalling in the northeast, and one major hurricane landfalling in North Carolina. Obviously, any group using 1954 as an analog are indicating that the Northeast and East Coast are at high risk this year. On the other hand, we don’t see the connection. Heading into the 1954 season, there were already signs of stronger than normal ridging developing over the central Atlantic and below normal heights over the Carolinas and Northeast. This year, there are more indications of central Atlantic troughing and the East Coast is under the influence of the eastern flank of the Gulf Coast ridge. A congregation of storm tracks may develop over the central/western Atlantic this summer, but not along the East Coast.

Canadian Maritimes

An above average number of tropical cyclones are expected to recurve in the central and western Atlantic, and the evolving steering pattern is indicative that some of the westernmost recurving storms may pass very close to the Maritimes. After analyzing the behavior of dozens of tropical cyclones that recurved over the central Atlantic in our analogs, we do expect one to two tropical cyclones to threaten the Canadian Maritimes this season.

Bahamas

The majority of threats are forecast to originate in the northwest Caribbean Sea rather than central Atlantic this season. The 500mb steering pattern that has steadily evolved over the course of the year is conducive for several tropical cyclone recurvatures east of the Bahamas. On the other hand, tropical cyclones that develop in the central or northwest Caribbean may also be susceptible to recurvature over Cuba and the Bahamas. One to two tropical cyclones may threaten the Bahamas from the southwest this season. The possibility of these cyclones being minimal or moderate hurricanes cannot be ruled out. Further elaboration of the 2006 steering pattern can be read in the Cuba section.

Cuba

Considering most storms that strike southwest Florida initially pass through Cuba, the same forecast methods used to forecast southwest Florida activity have been applied for this section. The prospects of a hurricane or tropical storm cutting westward across the Western Indies into Cuba such as Georges of 1998 are essentially non-existent this year based on the 500mb steering pattern and March NAO. Therefore, this leaves us with the last possible major threat for Cuba: a late season monster coming from the western Caribbean Sea. This type of storm is not particularly common, and our research indicates that such an event probably will not occur in 2006. Provided ENSO becomes at least warm-biaed by autumn, any storm that forms in the Caribbean in October or later will have a hard time feeding off optimum conditions to support growth into a major hurricane. It is interesting to note that every late major hurricane that has formed in the western Caribbean Sea has occurred when ENSO was either cool-biased or in a La Nina episode. Neither conditions are expected this year. However, it should be cautioned that if ENSO does somehow slip into cool biased territory later this year, there would be more concern for a late season major hurricane for Cuba. The very warm ATC and western Atlantic troughing in combination with the favorable ENSO would both make such a scenario much more likely.

Nonetheless, that is not to say Cuba will not be impacted by several tropical storms or even minimal hurricanes. The strong Gulf coast ridge and troughing over the western Atlantic, as stated in the Florida section, will be conducive for tropical cyclones in the northwestern Caribbean Sea to track northward towards Cuba and Florida. One to two named storms are forecast to impact Cuba during the season from the Caribbean Sea, any one of them possibly being a minimal hurricane.

Hispaniola, Puerto Rico, and Lesser Antilles

Aside from the rare late-season exceptions such as Lenny in 1999, most tropical cyclone activity that strikes these islands comes from the Mean Development Region. The negative March NAO has promising implications for the Lesser Antilles and Puerto Rico. Out of the 16 recorded years with a negative March NAO, only 1954 and 1964 saw a major hurricane impact any of these islands. Convincingly enough, both of these years featured abnormally strong ridging in the subtropical Atlantic Basin between 20 degrees and 30 degrees latitutde. This enabled the rogue Mean Development Region major storm to get shoved westward towards these islands as opposed to staying adrift at sea. 2006’s springtime steering layers in the subtropical Atlantic Basin are dominated by lower than normal heights and troughing. This is much more in line with the typical negative NAO years. Therefore, a major hurricane landfall in Puerto Rico and the Lesser Antilles can be pretty much ruled out this year. Chances are also low for Hispaniola, but not quite as much so for a special reason. The orientation of the troughing this spring places its base just above Hispaniola. Although tropical cyclones to the south are frequently known to bypass the base of a mean trough during the peak of the season, this is harder to do towards October when the troughing deepens. For instance, the spring Atlantic Basin pattern in 1963 was very similar to this year’s, especially in regards to the location of the trough base. Sure enough, this trough was able to pull Flora, a late September and early October major hurricane, northward while it was in the central Caribbean Sea. Flora slowed down considerably at the point of recurvature but hit both eastern Cuba and Hispaniola before shooting out to sea. If a storm enters the eastern Caribbean Sea late enough in the season, a similar scenario is very possible this year.

Having said that, it does not appear these islands will be immune to tropical storms or even weaker hurricanes. Many of the negative NAO years that also featured a very warm ATC, including 1951, 1958, 1969, 1981, 2001, and 2005, tended to have at least one weak tropical cyclone impact the islands. This will likely be the case this year as well. A minimal hurricane, such as Emily in 2005, is not completely out of the question.

Eastern Yucatan Peninsula and Central America

We are forecasting at least one storm to enter the eastern Caribbean Sea during the peak of the season. Considering such a storm would likely miss the base of the trough situated north of the Dominican Republic, this leaves it nowhere to go but westward. Curving northward towards Cuba and Florida is possible but actually less likely for a westward-tracking Caribbean storm than for in-situ western Caribbean systems. Such a track has happened before, the most notable being Donna in 1960 and Charley in 2004. However, both years featured low 500mb heights over Florida during the spring, signifying the onset of a strong east coast trough but ridging in the subtropical Atlantic to the east. This pattern is not the case this year. While any storm that forms in the northwest Caribbean Sea may be prone to get pulled northeastward by the central Atlantic troughing, the chances are much lower for a storm that has already missed the main connection with the trough and is still chugging westward at a lower latitude. The destiny of this type of storm is logically Central America. Such a scenario is likely to occur this season due to reasons outlined in prior sections. Furthermore, there is always the possibility that a tropical cyclone develops in the southwestern Caribbean Sea far enough under the late season troughing to avoid getting pulled poleward. Based on this information, one to two named storms are forecast to strike Central America or the Yucatan Peninsula this season. The plausible westward-moving system during August or September should encounter favorable enough conditions in the western Caribbean Sea to support intensification into a hurricane, possibly a major hurricane, before landfall.

VII: Monthly Breakdown

The Atlantic Basin hurricane season officially spans six months, beginning on June 1 and ending on November 30. Unlike landfall and regional forecasting, it is very hard to venture out and predict tropical cyclone activity for each month or pair of months by observing the recent patterns alone. Therefore, we looked primarily at climatology and data from analog years for this section of the forecast.

June and July

Generally speaking, the first two months of the Atlantic Basin hurricane season are relatively quiet. On average, one to two named storms form in these months combined. Last year saw the record development of seven named storms and two major hurricanes. Although the insane activity continued throughout the rest of the season, the amount of activity that occurs in June and July does not necessarily have any bearing on how active the remaining four months or the season altogether will be.

There are two major factors towards June and July activity: winter ENSO and June-July ENSO. Our research strongly indicates that years where an El Nino was present the preceding winter tend to have above average tropical cyclone activity in the first two months of the season. However, years with neutral ENSO during the two months themselves is also favorable for more storms. Although the former is difficult to synoptically prove, it is reasonable that neutral ENSO is the most conducive for early activity. During an El Nino year, other factors aside, the late spring and early summer pattern tend to feature an abnormally strong and low jet stream. The strong zonal flow associated with this is not favorable for early tropical cyclone development. In a La Nina summer, there are usually much less frontal features dipping down into the tropics in the first place. This is a problem as well, as many early season storms are spawned in part by remnant frontal boundaries. During a neutral ENSO, fronts are not completely hindered, yet the longwave flow is still amplified enough to allow for tropical development off frontal tail-ends.

This past winter was under a weak La Nina, but a neutral ENSO is currently present as we head into June and July. Thus, we are faced with two conflicting factors. Recent warm ATC years that did not have a winter El Nino and similar spring ENSO conditions include 1979, 1981, 1989, 1996, and 2001. All of these years had between one and three named storms before August. However, this can be narrowed even further. The years in this sample that had early activity in the Mean Development Region, 1979, 1989, and 1996, all had neutral or positive March NAO values, which was not the case this year. Taking this into account, one to two named storms are forecast to develop before August this season.

August and September

Atlantic Basin tropical cyclone activity tends to experience a fairly sharp increase during the month of August, particularly after August 15. August and September are by far the most active months of the season, with the climatological peak of being in early to mid September. In almost all cases, an above average hurricane season equates to above average activity in these two months.

Upon investigating previous active hurricane seasons, we noticed two separate camps concerning tropical cyclone activity during the peak. One group contains years that featured a general range of six to eight named storms in August and September, which is above normal, but not overly so. On the other hand, there are other years that had over ten named storms in the same timeframe, a rather explosive amount of systems for such a duration. This poses the question of exactly how active the peak two months will be this season. We further examined the ten years since 1950 with ten or more named storms and interestingly enough discovered that only six of them were during a warm ATC. Furthermore, all six of these warm ATC years had warm ENSO conditions the preceding winter. The remaining four cool or neutral ATC years had the opposite, a cool winter ENSO. The reasoning for this dichotomy is unclear. A logical hypothesis is that residual El Nino conditions coupled with warm ATC, or residual La Nina coupled with cool ATC, both equally allow more development from frontal-tropical wave interactions. In any event, the March NAO logically also plays a role since many storms during the peak form in the Mean Development Region. This is another restriction on this year’s August and September activity.

The combination of a warm ATC, winter La Nina, and negative NAO highly suggests no more than eight named storms during the peak this year. Other recent years where the first two states were case include 1989, 1996, 1999, and 2001, though 2001 is the only one on the list that also had a negative NAO. It thus comes to no surprise that 2001 had the lowest amount of hurricane and major hurricane activity out of this sample. Taking everything into account, six to eight named storms are forecasted to develop during August and September, with four to five being hurricanes, and around two of those achieving major hurricane strength.

October and November

When October approaches, a noticeable decline in Atlantic Basin tropical cyclone activity is observed. On average, there are two to three named storms in October and November, which is far less than what is typically the case in August and September but slightly more than the first two months. However, in uncommon cases, there can be more activity during these months than around the peak, such as what was observed in last year.

Our research indicates an above average level of storms during the latter portion of the season. There are two primary reasons for this presumption: a very warm ATC and a neutral ENSO. Upon examining all of the past 55 seasons or so, we noticed that the stronger the ATC, the more activity observed in the last two months. This is not surprising considering a strong ATC is favorable for Atlantic Basin activity as a whole. Also, the warmer SSTAs that occur in tandem with a strong ATC increases the likelihood of late season cutoff lows acquiring warm cores and becoming tropical cyclones. Having said that, the relation with ENSO is a bit more interesting. When a moderate or strong El Nino is in place, activity during the last two months is almost always reduced below average due to the stronger subtropical jet stream and associated westerly shear over the basin. Conversely, and to no amazement, more intense tropical cyclones are observed late in the season when a La Nina is present. However, it is found that seasons with neutral or even weakly warm ENSO tend to have a higher amount of storms than what is seen in a La Nina, especially when coupled with a strong ATC. The most logical reason for this is similar to what was outlined in the June to July sub-section. While a La Nina favors the stronger low-latitude systems, there are generally fewer cut-off lows in the subtropics, which often transfer to warm-core tropical cyclones in the late season.

Since a neutral or weak warm ENSO and a warm ATC are both in the forecast this autumn, we expect at least five named storms to form after September, with two to three of those strengthening into hurricanes. It should be noted that the only years that had an ATC comparable to this year’s level coupled with neutral autumn ENSO are 2001 and 2005. Both of these years saw more tropical cyclone activity the last two months than August and September, albeit most of the storms were in the subtropics and did not affect land. A similar case of multiple cutoff tropical cyclones cannot be ruled out this year if the ENSO does not become too warm. It does appear ENSO will be at least warm-biased, and this therefore lessens the chances of a major hurricane during October or November. If ENSO ends up cooler than expected, however, a late major hurricane would be much more likely since one has occurred in every non-El Nino autumn since 1995.

VIII: Summary and Conclusion

The recent upswing in tropical cyclone activity in the Atlantic Basin appears far from being over. A strong ATC combined with neutral ENSO conditions should allow the above normal trend in tropical cyclogenesis to continue into the 2006 season. There are some notable characteristics that stand out in our preseason data. Near average activity is forecast in the Mean Development Region, with most tropical cyclones recurving out to sea. Below normal heights over the central Atlantic may act as a protective barrier of tropical cyclones for the US East Coast. Any tropical systems that manage to undercut the below normal heights and enter the central and western Caribbean Sea may be prone to becoming significant hurricanes. The threat of major hurricane landfalls in the Caribbean is relatively low starting with the Lesser Antilles, but the threat gradually increases with longitude in the central and western Caribbean. Ridging over the southern states and troughing over the central Atlantic should keep any significant, low-latitude tropical cyclones south or east of the US Gulf Coast. However, there is a moderate risk of tropical storm or minimal hurricane impacts in southwest Florida and the Texast coast. The Mexican Gulf Coast faces a similar risk. Finally, our forecast number of systems is presented below. While 2006 is expected to be above average, the level of activity is expected to be far less than that observed in 2005. Last year, extremely warm sea surface temperatures across the entire Atlantic Basin set records and spawned 28 named storms in the process. Sea surface temperatures are above average this year, but they do not rival the anomalies of 2005.

IWIC 2006 Atlantic Basin Hurricane Season Forecast

Parameter 2006 Forecast Long Term Average
Named Storms 14 11
Hurricanes 8 6
Major Hurricanes 4 2

Regardless of our exact expectations for 2006, one in a hurricane prone area should always be prepared for a landfall well in advance. Even if 2006 hurricane activity unexpectedly turns out to below normal, it only takes one intense landfalling hurricane to make the season a devastating one. A well-known example of this is the 1992 hurricane season. This was a well below average year by almost all activity measures, yet it was the year of Category Five Hurricane Andrew, which slammed into southern Florida and resulted in over 30 billion dollars of damage.

This seasonal forecast will not be updated during the season, though smaller updates will be posted within our daily tropical weather discussions if necessary. A post-review of the 2006 season will be underway by December 2007. This allows us to analyze how all of our seasonal forecast methods fared through the 2006 season, and better prepare our 2007 forecast. By January 2007, preliminary research on the 2007 Atlantic hurricane season will begin.

2007 Atlantic Basin Hurricane Season Forecast

STRACT

Data obtained throughout the past several months indicates that 2007 Atlantic Basin hurricane activity will be somewhat above the long-term average, with an estimated 13 named storms, 8 hurricanes, and 3 major hurricanes. An abnormally high number of tropical cyclones will form east of the Lesser Antilles during the bimonthly period of August and September, with at least one significant hurricane striking the northeast Caribbean. The Yucatán Peninsula also faces a high risk of a major hurricane strike during the final third of the season. No tropical cyclone landfalls are expected along the United States mainland.

1. Introduction

This is the fifth Atlantic Basin hurricane season forecast issued by the Independent Weather Information Center. The primary parameters that are known to affect the frequency and steering of tropical cyclones in the Atlantic Basin have been closely analyzed throughout this off-season. A thorough explanation and forecast of these factors are outlined. Analogous pattern and parameter combinations derived from 57 years of historical climate data have also been examined to further justify the anticipated synoptic setup over the northern hemisphere. The aforementioned methodology has been utilized to forecast not only seasonal, but also monthly, regional, and landfalling tropical cyclone activity.

While an overwhelming consensus of members within the meteorological community dismisses the idea of providing accurate landfall forecasts months in advance, it is the long-term goal of IWIC to prove that it is in fact possible. Countless hours of research and resulting statistical correlations combined with theory have led the authors to believe, in convincing fashion, that several recent findings are of significance. Bare in mind this forecast is experimental and unofficial, hence IWIC is not liable for one’s actions taken based on the information being presented. Please read the disclaimer.

Several verification guidelines are strictly followed. First, any subtropical or tropical cyclone formation before June 1 or beyond November 30 will not be included within the verification of this seasonal forecast. Subtropical Storm Andrea has not been included in the forecast totals. Second, classified depressions are not featured in any aspect of the seasonal verification. Third, a depression that develops in a particular region, but moves into a secondary region before becoming a named storm will be verified as a named storm formation in the region in which it officially becomes a named storm. Fourth, a depression that develops in a particular month, but does not strengthen into a named storm until the following month will be verified as a named storm formation in the month in which it officially attains a name. Finally, any named storm that strikes the Gulf (Atlantic) coast of the Florida peninsula and re-emerges into Atlantic (Gulf) waters will not be considered a landfall along the east (west) side of Florida. This guideline also applies for western and eastern coastal areas of the Yucatán Peninsula.

2. 2006 Methodology Modification and Forecast Verification

Although there was moderate success in 2003 and 2004, neither the landfall nor total tropical cyclone activity forecasts verified well in 2005. It would have been completely imprudent to apply the same methodology to forthcoming forecasts after it displayed no skill in 2005. Upon an intense post-review, it remains accepted that several, pre-2006, hypothesized correlations were flawed due to misrepresentative statistics. Thus, many of the original forecasting methods were abandoned and a new methodology was introduced in the 2006 Atlantic Basin hurricane season forecast.

Confidence in the new methodology increased leading up to the 2006 season despite the recognized failures of 2005 and forecast discontinuity between IWIC and other respected groups and agencies. The majority of members within the media and meteorological community began to warn that hurricane season 2006 would be hyperactive, and feature significant landfalling tropical cyclones. On the other hand, IWIC did not foresee a season of such hyperactivity and landfalls. Fortunately, the much advertised season of hyperactivity and destructive landfalls never materialized. Rather, the outcome was quite similar to IWIC’s expectations.

The 2006 total tropical cyclone activity forecast called for 14 named storms, 8 hurricanes, and 4 major hurricanes. In reality, only 10 named storms, 5 hurricanes, and 2 major hurricanes formed. It is somewhat disappointing that the actual totals did not match the projected estimates. However, it should be noted that the three longstanding and highly respected seasonal forecasting agencies had indicated there would be at least as much activity as forecast by IWIC. The following table compares the seasonal forecast totals released in May 2006.

Comparison of May 2006 Atlantic Hurricane Season Forecasts

Parameter
IWIC
TSR
NOAA
CSU
Actual
Named Storms
14
14.6
13-16
17
10
Hurricanes
8
7.9
8-10
9
5
Major Hurricanes
4
3.6
4-6
5
2

Regardless, the fact that most agencies were guilty of forecasting more activity than observed is no excuse for IWIC’s forecasting shortfalls. The unexpected development of El Niño conditions in the equatorial Pacific by October was the primary cause of IWIC’s overestimation. If one were to break down the monthly tropical cyclone activity forecasts, it would become evident that 7-10 named storms, 4-5 hurricanes, and 2 major hurricanes were projected to form by October 1. In reality, 10 named storms, 5 hurricanes, and 2 major hurricanes had developed by the end of September. In other words, the monthly observed activity was easily meeting IWIC expectations until equatorial Pacific conditions reached El Niño thresholds in October. Furthermore, it is no surprise the forecast of 5 named storms and 2 hurricanes during the bimonthly period of October-November did not verify. Had the late onset of El Niño conditions been accurately diagnosed in May, no more than 12 named storms would have been forecast for 2006. Additional adjustments to the ENSO forecasting approach have been incorporated into the 2007 seasonal forecast, thus reducing the probability of such flawed ENSO forecasts in the future. In the meantime, it is the opinion of the authors that the 2006 total activity forecast was, in large part, a success. Such skill has been consistently displayedsince the first IWIC forecast in 2003.

With all that said, the success of IWIC landfall forecasts is of greater importance. Thankfully, the 2006 IWIC landfall forecast verified quite well. The following landfall forecasts verified with no question: no landfalling storms along the storm-ravaged north Gulf coast, 1-2 named storms exiting the Caribbean Sea and striking the Florida peninsula, no significant landfalls along the east side of the Florida peninsula, no direct hits along the northeast United States, 1-2 threats to the Canadian Maritimes, minimal storm threats to the Bahamas originating from the Caribbean Sea, 1-2 minimal storm hits on Cuba from the Caribbean Sea, and 1-2 minimal threats to Hispaniola, Puerto Rico, and the Lesser Antilles.

Some of the landfall forecasts did not verify, however. Approximately 2 minimal tropical cyclones were forecast to originate in the southwest Gulf of Mexico and impact Texas and northeast Mexico, but these storms never materialized. This forecast could have been corrected with the additional data acquired since last May. Nonetheless, it is interesting to note that multiple tropical disturbances in the southwest Gulf of Mexico were nearly classified as tropical cyclones by the National Hurricane Center before moving inland over Mexico and Texas. The second incorrect landfall forecast included 1-2 tropical cyclones, one possibly being intense, impacting Central America. It is presumed that the onset of El Niño during the latter half of the 2006 season greatly diminished Central America’s chances of being directly impacted by a tropical cyclone. Finally, no more than a brush was expected in North Carolina, but one tropical storm landfall was observed. This was more of an error in phraseology than methodology, as several weak tropical cyclones directly struck North Carolina in selected analog years. Nevertheless, the primary idea was there would not be any significant hurricane landfalls along the East coast.

Additional skill was displayed in forecasting regional activity. For instance, 4 named storms, 2-3 hurricanes, and a major hurricane were forecast to develop in the Mean Development Region, which is located between the Lesser Antilles and west coast of Africa. Over the course of the season, 4 named storms, 2 hurricanes, and a major hurricane originated from the area. Up to two storms were forecast to, “probably enter or form close to the eastern Caribbean Sea,” hence tropical cyclones Chris and Ernesto. Above normal activity was anticipated in the west Atlantic due to a combination of in-situ developments and recurving storms from other regions, and such was in fact the case. Tropical cyclone activity estimates for the west Caribbean Sea and west Gulf of Mexico did not fare as well, hence the inaccurate landfall forecasts among those regions. If nothing more, one should at least be able to recognize that the forecast unquestionably nailed the overall pattern observed during the 2006 hurricane season.

The verification of the IWIC 2007 seasonal hurricane forecast will be even more promising based on what is hereby assumed to be positive additions to the forecast methodology. The preexistence of an applicable forecast technique to build upon, as opposed to the lack of such in early 2006, was a significant advantage in the construction of the 2007 forecast. Moreover, the latest modifications being implemented in the 2007 forecast are intended to reduce the types of errors observed in 2006, which fortunately were few and far between.

3. Summer-Fall El Niño Southern Oscillation

The El Niño Southern Oscillation (ENSO) is an important parameter concerning Atlantic Basin tropical cyclogenesis. ENSO is most notably characterized by significant variations in sea surface temperature anomalies (SSTAs) in the equatorial Pacific, though alterations in sea level pressure anomalies (SLPAs), trade winds, and convection are also observed. Warm (cool) SSTAs are associated with El Niño (La Niña) episodes, and if SSTAs are neither warm nor cool, ENSO is considered neutral.

Once an El Niño (La Niña) event takes hold, strong (weak) upper-level westerly winds dominate the low latitudes of the Atlantic Basin, thus hindering (enhancing) hurricane development from tropical waves and disturbances along the intertropical convergence zone. Being that El Niño can allow for more baroclinic-induced development in the higher latitudes, there is only a small difference in named storm frequency between El Niño and La Niña episodes. Nonetheless, more hurricanes and intense hurricanes are generally observed in La Niña or even neutral ENSO conditions.

Current Status

El Niño conditions developed in October 2006. Warm SSTAs peaked in ENSO Region 3.4 on December 6 with a value of +1.4ºC. SSTAs in Region 3.4 have steadily declined since early December and are currently entering negative territory. Furthermore, a large pool of negative SSTAs below the ocean surface of the equatorial Pacific has been present since December. Subsurface cooling is often one of the first precursors to the formation of a La Niña episode. Some mild warming has recently occurred in tandem with a traversing Kelvin wave. This will act to temporarily delay, but not prevent, La Niña development. Another important aspect of the ENSO is the Southern Oscillation Index (SOI), defined by SLP differential between Tahiti and Darwin, Australia. Negative (positive) values correspond to El Niño (La Niña), and as one would expect, daily negative values dominated the SOI during the late formation of El Niño in 2006. The monthly SOI tanked in January 2007 with a value of -7.3. In recent months, both daily and monthly SOI values have become increasingly positive. The April SOI value was -3.0. That reading is slightly higher than the -1.4 value recorded in March, but some fluctuations in the SOI are to be expected. The overall slow trend toward a more positive SOI remains evident.

Climatology

While the sole use of climatology is ill-advised, it is a vital component of long-range ENSO forecasting methodology. One of the climatological research methods used is the evaluation of past and current values of the Multivariate ENSO Index (MEI). The MEI helps determine the overall condition of ENSO and its level of influence on atmospheric circulations. The index accounts for the SOI, equatorial convection, and other global conditions known to be affected by ENSO. Positive (negative) values of the MEI correspond with El Niño (La Niña) conditions. The MEI recently peaked at +1.3 in November 2006. There was a secondary peak in January 2007, but MEI values have dramatically fallen to near 0 within the last three months. The peak MEI value in late 2006 followed by a steady decrease into neutral territory during the early spring is an important trend to note. The following five MEI analogs were then selected and analyzed: 1963-1964, 1965-1966, 1972-1973, 1987-1988, and 1994-1995. Three of those analogs featured La Niña conditions throughout the following hurricane season. The two exceptions, 1966 and 1995, featured ENSO cool bias and late season La Niña conditions, respectively. None of the hurricane seasons that followed had to contend with El Niño or even warm bias ENSO conditions. Thus, trends within the MEI suggest that there is little to no chance of El Niño this summer, but there is at least an 80 percent probability of La Niña conditions by fall.

A second climatological method used to forecast ENSO is more basic yet equally as effective. The observation of trends in trimonthly values of ENSO region 3.4 SSTAs can benefit ENSO forecasting much like those observed within the MEI. The latest El Niño peaked during the trimonthly period of November-December-January with a 3.4 region SSTA value of +1.1ºC. Soon after, trimonthly values decreased substantially. SSTAs moderated by 0.8ºC between the trimonthly periods of NDJ and JFM. Similar trends were observed in 1963-1964, 1987-1988, and 1994-1995. La Niña conditions were present throughout the 1964 and 1988 hurricane seasons. Similarly, La Niña made a late appearance during the 1995 season.

A third climatological method of ENSO forecasting based on global SLPA patterns is being studied. Additional elaboration of the specifics is not desired at this point in time. Nonetheless, this scheme is much more sophisticated and potentially more valuable to long range ENSO predictions than simple observation of MEI and trimonthly SSTA trends. The method, albeit in the experimental stage, is signaling that La Niña conditions will be established by the trimonthly period of June-July-August at the latest.

Finally, a new technique involving a connection between ENSO and solar activity is in the works. In fact, this scheme may permit accurate ENSO forecasts up to several years lead time. While the details will have to be explained in a future paper, it can be said that the method, combined with the aforementioned data, is indicating that at least cool bias ENSO conditions will form this year and possibly last through the end of 2008.

Model Forecasts

Little weight was given to the available ENSO model forecasts this year. The model consensus more often than not seems to miscalculate the timing and development of crucial ENSO episodes in the long range. Regardless, all of the available model data suggests that ENSO will either remain neutral or strengthen into La Niña by the summer. It should be noted that CLIPER and GMAOGCM, two of the more reliable ENSO models that correctly predicted the onset of the 2006 El Niño, are predicting cool ENSO conditions by the peak of the hurricane season.

2007 ENSO Forecast

The El Niño episode that developed in late 2006 and persisted through early 2007 has dissipated and will not return this year. Moreover, ENSO is forecast to reach La Niña criteria by September and last through the second half of the Atlantic hurricane season. This solution is supported by the following: recent trends in the SOI, moderating SSTAs over the equatorial Pacific, persistent subsurface cool anomalies, historical MEI analogs, trimonthly ENSO SSTA analogs, two experimental climatology methods, and a consensus among ENSO forecast models. The anticipated La Niña will act to enhance hurricane and major hurricane activity in the tropical Atlantic Basin during the trimonthly period of August-September-October.

4. Summer-Fall Atlantic Multidecadal Oscillation

The Atlantic Multidecadal Oscillation (AMO) is a long-term pattern of SSTA variability in the North Atlantic Ocean. It is theorized that the oscillation is dependent on decadal density-driven changes in the thermohaline circulation. The warm (cool) phase is known to enhance (suppress) hurricane activity. The most notable aspect of the warm (cool) phase is above (below) normal SSTAs across the tropical Atlantic Basin, which provides more (less) energy for tropical cyclones to sustain deep convection. Since 1995, the AMO has been in a predominantly warm cycle, which explains the several significantly above average hurricane seasons that have occurred over the past 12 years. However, the AMO does occasionally fluctuate to the opposing phase of the long-term cycle.

From mid 2003 to this day, SSTAs in the tropical Atlantic Basin have, for the most part, remained well above average. However, a new experimental model that may explain as much as 16 percent of tropical Atlantic Basin SSTA variance suggests that modest cooling will gradually occur throughout the remainder of 2007. In fact, current SSTAs could moderate to near neutral levels during the peak of the hurricane season. While there is confidence in this scheme, additional elaboration of model specifics is not desired at this point in time. Considering summer and fall tropical Atlantic Basin SSTAs will not reach the extreme levels observed over the past 4-5 years, the warm AMO will only moderately enhance tropical cyclone activity in 2007.

5. Other Factors

The combination of La Niña conditions in the equatorial Pacific and a slightly warm AMO certainly suggests that an active Atlantic Basin hurricane season is likely. However, there are several other parameters that must be accounted for to accurately forecast both monthly and total activity as well as formation and track distribution.

Spring North Atlantic Oscillation

The North Atlantic Oscillation (NAO) is an atmospheric pattern over the North Atlantic that is defined by differences in sea level pressure between the Icelandic Low and Azores High. Positive (negative) NAO values denote higher (lower) pressures near the Azores compared to Iceland. Although the NAO is a central figure in the concurrent steering pattern across the Atlantic Basin, it is extremely variable on a monthly and even weekly basis. However, an in-depth reanalysis of the last 57 years indicates that spring NAO values have a lag influence on large-scale atmospheric conditions that evolve over the Atlantic Basin during hurricane season. The importance of the positive NAO observed this spring is discussed in detail in later sections.

Spring North American Pattern

Analysis of the 57 year climatology database indicates that the springtime pattern over the continental United States, northeast Pacific Ocean, and surrounding areas has a lag affect on large-scale atmospheric conditions that evolve over the Atlantic Basin during the hurricane season. As such, the authors have proposed a unique parameter hereby called the Spring North American Pattern (SNA). The proposed four phases of the pattern have been found to influence homegrown tropical cyclone frequency and steering patterns surrounding the southeast United States and Central America. The significance of the Phase 2 SNA pattern observed during much of spring 2007 will be discussed in later sections of the forecast.

Winter El Niño Southern Oscillation

Winter values of the ENSO are vital to several aspects of the seasonal hurricane forecast. First and foremost, winter ENSO episodes are known to have a lag influence on large-scale atmospheric conditions well after they dissipate. Therefore, the winter ENSO signal is given weight when analog springtime patterns are selected. Second, winter ENSO has been found to have a direct influence on tropical cyclone landfall probabilities in certain regions. Finally, it was recently discovered that winter ENSO episodes play a key role in determining early season tropical cyclone frequency when other summertime parameters are less pronounced than usual.

Summer-Fall Quasi-Biennial Oscillation

The Quasi-Biennial Oscillation (QBO) is a periodic variation in the direction of stratospheric winds across the deep tropics. The two phases, easterly and westerly, generally last from 12 to 16 months, with the easterly phase often having a slightly longer duration. The westerly phase of the QBO peaked last June with a value of +11.47. Afterwards, the QBO steadily declined and has just recently transitioned to the easterly phase. The QBO will continue to fall throughout this year, with the next transition not occurring until sometime in 2008. While the QBO has a moderate affect on tropical cyclone activity in the Mean Development Region, it is otherwise one of the lesser factors considered in this forecast.

Summer-Fall Pacific Decadal Oscillation

The Pacific Decadal Oscillation (PDO) is a multi-decadal pattern of high and low pressure systems in the north Pacific Ocean, sometimes seen as a longer-term version of ENSO. Unlike ENSO, the PDO index is calculated by spatially averaged monthly SSTAs over the northern, as opposed to equatorial, portions of the Pacific Ocean. The PDO switched to a long-term warm cycle in 1977 and aside from a few fluctuations has remained in that phase up to the present time. However, the PDO has been closer to neutral since mid 2006. In fact, a recently discovered link between the PDO and solar activity suggests that it will indeed switch to a long-term cool state later this year as La Niña conditions unfold in the equatorial Pacific. Although the PDO is not known to exhibit a significant influence on year-to-year Atlantic Basin tropical cyclone activity, one study hints that its long-term state influences United States landfall odds.

6. Activity By Region

The Atlantic Basin has been divided into five regions to help portray the anticipated tropical cyclone formation and steering tendencies of 2007.

Mean Development Region (south of 20ºN, east of 60ºW)

The majority of tropical cyclogenesis observed in the Atlantic Basin is initiated by tropical waves that migrate from Africa to the Mean Development Region, hence the name. Several of the waves that trigger cyclogenesis do so within the borders of the region. The remaining percentage of embryonic tropical cyclones form upon entering the Caribbean Sea, west Atlantic, or Gulf of Mexico. Common logic dictates that warm SSTAs and a lack of El Niño conditions would result in abnormally high activity in this area. However, the necessary formula is not that simple. Several seasons have featured warm SSTAs, a lack of El Niño, and average to below average tropical cyclone activity east of the Lesser Antilles. For example, record warm SSTAs and cool-bias ENSO conditions were observed in 2005, but as active as the season was overall, the Mean Development Region escaped with only two weak named storms. This conundrum has been a subject of study post 2005, and sure enough a critical parameter of Mean Development Region activity was discovered: spring values of the NAO.

After analyzing 57 years of data, it has been concluded that positive (negative) spring values of the NAO correspond with enhanced (suppressed) tropical cyclone activity in the Mean Development Region. Hurricane seasons following positive NAO spring months yield 1.0 named storms, 0.4 hurricanes, and 0.3 major hurricanes more than those following negative spring months. The correlation is magnified when AMO values are positive. Warm AMO hurricane seasons that follow positive NAO spring months yield 2.5 named storms, 1.5 hurricanes, and 0.8 major hurricanes more than warm AMO seasons following negative spring months. The lengthy process by which spring values of the NAO affect Mean Development Region tropical cyclone activity will have to be explained in a future paper. In short, however, opposing modes of the spring NAO have conflicting effects on the large-scale atmospheric circulation. Moreover, atmospheric fingerprints of the spring pattern persist over the Mean Development Region during the summer months. Summer variability of the NAO does not override the summer pattern set forth by the spring NAO dipole pattern because the dipole is considerably less intense during summer.

Warm AMO and La Niña conditions are forecast this hurricane season. While warm AMO combined with neutral and especially La Niña conditions typically feature above normal activity in the Mean Development Region, such is never a guarantee unless spring NAO conditions are positive. Spring 2007 did feature a positive NAO. Therefore, it has been concluded that abnormally high tropical cyclone activity will be observed in the region. All three parameters aligned in the same fashion during the 1995 and 1998 hurricane seasons. 1995 and 1998 featured 9 and 7 named storms, 6 and 3 hurricanes, and 1 major hurricane each in the Mean Development Region, respectively. All three measurements of tropical cyclone activity were exceptionally high compared to the climatological average in each of those seasons. 2007 may rival what was observed in the deep tropical Atlantic during 1995 and 1998, but slightly less activity is anticipated overall. The westerly QBO of 1995 and remarkably warm AMO of 1998 are thought to have maximized the favorable conditions set forth by ENSO and the NAO. The current easterly QBO and steadily moderating AMO should place somewhat of a ceiling on total numbers in 2007. Thus, 7-8 named storms, 4-5 hurricanes, and 1-2 major hurricanes are forecast to originate from the Mean Development Region. It should be noted that such numbers are substantially higher than the long-term climatological averages of 3.0 named storms, 1.4 hurricanes, and 0.5 major hurricanes.

Northeast Atlantic (north of 20ºN, east of 65ºW)

Unlike the Mean Development Region, tropical cyclogenesis that occurs in the northeast Atlantic is typically a result of baroclinic forcing as opposed to initiation by tropical waves. However, tropical cyclones that develop in the Mean Development Region often recurve poleward and move into the area. While the northeast Atlantic is by far the largest region covered in this forecast, it also tends to be the most ignored due to the fact that most tropical cyclones that traverse these waters do not impact land.

To assess the amount of tropical cyclones that will enter the northeast Atlantic, the spring mid-level pattern in the general area was analyzed. One noticeable characteristic of the past spring pattern was a large weakness centered near 60ºW. The weakness acted to separate two high pressure systems, one over the continental United States and the other over the northeast Atlantic, respectively. With 7-8 named storms forecast to develop in the Mean Development Region, it is reasonable to suspect that many storms will recurve into the northeast Atlantic along this weakness. In fact, a concentrated recurving corridor may set up along the mean trough position between 55-65ºW. An estimated 5-6 named storms, 4-5 hurricanes, and 1-2 major hurricanes are expected to move into the northeast Atlantic from the Mean Development Region and west Atlantic.

Although there will certainly be numerous tropical cyclones entering the northeast Atlantic, it does not appear that there will be much tropical cyclone development within the region. Several studies were conducted to better understand how various parameters influence development in the northeast Atlantic. The most promising study is primarily based on the winter ENSO. Seasons following both winter La Niña and neutral ENSO conditions yield an average of 1.4 named storms, 0.85 hurricanes, and 0.1 major hurricanes developing in the northeast Atlantic, whereas the average for seasons following an El Niño is 2.3 named storms, 1.5 hurricanes, and 0.2 major hurricanes. Interestingly, years with winter El Niño conditions followed by neutral ENSO conditions average 3.5 named storms, 2.7 hurricanes, and 0.5 major hurricanes forming the northeast Atlantic. On the other hand, years with winter El Niño conditions followed by La Niña conditions average only 1.4 named storms, 0.9 hurricanes, and 0 major hurricanes. Of the latter years, only 1964 and 1998 had more than one named storm formation. Furthermore, two of the tropical cyclones in 1964 were simply delayed Mean Development Region developments. Such developments are less likely in warm AMO and positive NAO years. The physical reasoning behind such correlations is currently being investigated. With that said, 1-2 named storms and 0-1 hurricanes are forecast to develop in the northeast Atlantic.

West Atlantic (north of 20ºN, west of 65ºW)

Although the west Atlantic does not sustain the strongest hurricanes, tropical cyclones in the region often rapidly intensify uncomfortably close to the United States East coast. Furthermore, tropical cyclone formation via initiation of tropical waves or baroclinic forcing are both common in the west Atlantic, as are tropical cyclones moving into the area from the Mean Development Region and northeast Atlantic.

However, the said trigger mechanisms of tropical cyclogenesis are forecast to yield few formations during August-September 2007. Baroclinic-initiated tropical cyclogenesis occurs most frequently during El Niño episodes and cool AMO periods, but neither will be present this season. A high frequency of baroclinic-induced storms has also been noted during several La Niña episodes, but nearly all of them also featured cool AMO conditions. In fact, La Niña-dominated seasons that feature a cool AMO yield 1.1 more named storms than those with a warm AMO due to the increase in baroclinic-initiated development. In addition, the lack of any significant upper air troughing over the region, which was the case last spring, is often a precursor of less cutoff lows in the west Atlantic during the summer. Thus, the probability of development via baroclinic forcing is exceptionally low. Notwithstanding, it is not out of the realm of possibility that a few tropical waves will induce tropical cyclone formation in the portion of the west Atlantic bordered by the Bahamas, Bermuda, and the 65ºW parallel. This may be most likely to occur in July when conditions in the Mean Development Region are still seasonably unfavorable. Any tropical cyclone that does form in this quadrant of the west Atlantic would recurve northeastward due to close proximity of an upper air weakness near 60ºW. With that said, 2-3 named storms and 0-1 hurricanes are forecast to originate from the west Atlantic this season.

The lack of in-situ storms does not mean the west Atlantic will be void of multiple tropical cyclone tracks, however. An abnormally active Mean Development Region combined with an upper air pattern conducive for several long-tracking storms over the central Atlantic signifies an above normal number of tropical cyclones entering the west Atlantic. A large number of recurvatures are forecast along a weakness in geopotential heights near the 65ºW parallel, and half of the recurving cyclones are bound to briefly traverse west Atlantic territory. An estimated 3-4 named storms, 2-3 hurricanes, and 1-2 major hurricanes are expected to enter the region from the Mean Development Region and northeast Atlantic.

Caribbean Sea

Despite the fact that numerous tropical cyclones have passed through the east Caribbean with little complications, in-situ formation is rare due to the summer presence of an upper-level trough. This feature induces strong southwesterly shear, which is unfavorable for tropical cyclogenesis. In-situ formation in the east Caribbean is even less likely in warm AMO, La Niña, and positive spring NAO years. 1995 and 1998 featured all three conditions, yet neither featured a single in-situ formation. The aforementioned regimes greatly enhance tropical activity in the Mean Development Region, thus decreasing the number of delayed, tropical wave-initiated formations that commonly occur west of the 60ºW parallel. In-situ east Caribbean formation has been observed in only 25 percent of past La Niña-dominated seasons. Likewise, only 12.5 percent of seasons with a combination of warm AMO and positive spring NAO conditions featured in-situ formation. Consequently, 2004 was the only year with such a parameter combination that featured an east Caribbean formation, but El Niño conditions were also present. The AMO, NAO, and ENSO will all be in modes that are least conducive for in-situ formation this year. Thus, no tropical cyclones are forecast to originate in this area. However, 1-2 significant tropical cyclones are expected to pass through the far northeast Caribbean Sea given the recently strong mid-level ridging north of the Mean Development Region.

On the other hand, the springtime pattern over North America and the far north Atlantic combined with spring values of the NAO also argues against any Mean Development Region-originating tropical cyclones passing west of 75ºW in the Caribbean. Rather, more northerly tracks into the subtropical Atlantic region are favored due to the presence of a mid-level weakness located near 60ºW. In fact, any tropical cyclone that enters the Caribbean Sea is likely to recurve back into the Atlantic east of Hispaniola. Moreover, the lack of any east Caribbean-originating storms suggests it is unlikely that any tropical cyclones will enter the west Caribbean Sea.

Finally, no storms are expected to originate in the west Caribbean Sea until late September or October. 1995, 1998, and 2000 are the three sampled seasons that featured positive spring NAO, warm AMO, and La Niña conditions. 1995 is the only year that featured an early and late season in-situ formation. Hurricane Allison formed on June 3, 1995, but such an early formation is not likely in 2007 due to the early onset of La Niña (see section 7). Also, 1995 is the only positive spring NAO year to ever produce more than one named storm in the west Caribbean. Excluding 1995, none of the 18 of positive spring NAO years had more than one west Caribbean in-situ development. However, positive spring NAO conditions and the early onset of La Niña do not exclude the possibility of late season development. All three aforementioned years featured a late-season major hurricane, and this area is notorious for producing major hurricanes, especially toward the latter half of the season. The development of La Niña conditions combined with the presence of warm AMO alone greatly increases the probability of a late season major hurricane. Late season major hurricane formation has been observed in the west Caribbean during 7/8 (88 percent) of recorded La Niña and warm AMO years. Due to overwhelming statistical support, one late season major hurricane is forecast to develop in the west Caribbean Sea.

Gulf of Mexico

The Gulf of Mexico has sustained some of the most notorious hurricanes in the Atlantic Basin. Occasionally, low vertical wind shear, abundant moisture, and seasonably warm SSTs of the Gulf of Mexico align in a manner that can transform incipient systems into monstrous hurricanes. Since the Gulf of Mexico is almost completely surrounded by land, tropical cyclones under supporting conditions have no option but to impact coastal and inland communities. Such was the norm in the destructive 2005 hurricane season, with five major hurricane landfalls along the Gulf coast, including Katrina. In sharp contrast, only one tropical storm traversed the Gulf of Mexico in 2006, so high variability amongst even warm AMO years is apparent.

With that said, the Gulf of Mexico faces another relatively calm season. One of the most intriguing discoveries over the last few months was the connection between the spring pattern and Gulf of Mexico tropical cyclone variability. The SNA, as the authors call it (see section 5), has four phases based on geopotential heights over the continental United States and adjacent Pacific and Atlantic regions. The definitions of each phase will be explained in a future paper. The following statistics demonstrate how the varying configurations of the four phases influence Gulf of Mexico tropical cyclone activity: Phase 1 averages 4.9 named storms, 2.4 hurricanes, and 1.3 major hurricanes; Phase 2 averages 2.1 named storms, 0.9 hurricanes, and 0.1 major hurricanes; Phase 3 averages 3.0 named storms, 1.7 hurricanes, and 0.6 major hurricanes; Phase 4 averages 1.3 named storms, 0.7 hurricanes, and 0.3 major hurricanes. The variance in tropical cyclone activity amongst each phase is surprisingly low as well. Spring 2007 falls under Phase 2 of the SNA. Of the 14 years in the Phase 2 dataset, only one had over three named storms in the Gulf of Mexico. However, the geopotential height pattern in 2007 is very unique compared to past Phase 2 years. The anomalous mid-level ridging that has been present over the entire of the Gulf of Mexico this spring is actually more reminiscent of Phase 4. Regardless, the statistics from both datasets suggest below-average Gulf of Mexico activity overall.

Additionally, other statistical datasets suggest that the number of tropical cyclones entering the Gulf will be minimal. First, it has been concluded that there is little to no chance of a storm entering the Gulf from the west Atlantic and Florida. As aforementioned, an analysis of the spring pattern depicts a prominent trough centered near 60ºW, which is expected to persist in August-September. Thus, all tropical cyclones moving into the west Atlantic will lift poleward far away from the Gulf of Mexico as they follow the path of least resistance. Any tropical cyclone that forms in the west Atlantic will follow a similar track well to the east of the Gulf of Mexico. On the other hand, the late season major hurricane forecast to develop in the west Caribbean Sea will likely move into the Bay of Campeche in a weaker, sub-major state. After analyzing past years with tropical cyclones in the west Caribbean Sea, it is clear that the central Atlantic trough that became established this past spring is not positively-tilted or deep enough to pull a west Caribbean tropical cyclone northeastward into the west Atlantic. Therefore, 1 named storm, possibly a hurricane, is forecast to enter the Gulf of Mexico from the west Caribbean Sea.

Finally, it does not appear that many tropical cyclones will develop in the Gulf of Mexico either. The aforementioned high geopotential heights in the Gulf of Mexico suggest that tropical waves that would otherwise spawn a tropical cyclone will be kept south of the Gulf of Mexico this season. This is even more likely with persistently neutral to high geopotential heights across the Caribbean Sea, which will keep tropical waves from deepening enough to commence a poleward motion component. Moreover, only 1/12 (8 percent) of the Phase 4 SNA years had as many as two named storms form in the Gulf of Mexico: 1977. One of the storms was baroclinically-initiated, made possibly by the El Niño and cool AMO in place. Neither will be present this year. Thus, 0-1 named storms and 0-1 hurricanes are forecast to develop in the Gulf of Mexico during 2007.

7. Activity By Bimonthly Periods

The Atlantic Basin hurricane season officially spans six months, beginning on June 1 and ending on November 30. The season has been divided into three bimonthly periods to help portray the anticipated tropical cyclone formation and timing tendencies of 2007.

June-July

Typically, the first two months of the Atlantic Basin hurricane season are relatively quiet. On average, 1-2 named storms form before August. In 2005, a record-setting 7 named storms and 2 major hurricanes developed during this period. Although near record level activity continued throughout all three bimonthly periods of 2005, the amount of activity that occurs in June and July does not necessarily have any bearing on how much activity occurs in the remaining four months of the season.

The primary parameters known to influence June-July activity are the AMO, summer ENSO, and winter ENSO. It is no surprise that warm AMO conditions support above normal activity, albeit slightly. But one statistic could not be explained until halfway through this off-season. Warm AMO and neutral ENSO summers yield more activity than warm AMO and La Niña summers. It was discovered that winter values of the ENSO are to be implemented as part of the seasonal forecast, but only when the summer ENSO is expected to be neutral. When the summer ENSO is neutral, it leaves the door open for residual winter ENSO conditions to influence early season activity. Furthermore, residual winter El Niño conditions are most enhancing. The majority of the most active June-July periods fall within that dataset. It is theorized that residual El Niño effects and neutral summer ENSO conditions result in slightly above normal probability of baroclinic-induced formations and less than normal hindrance of deep tropical activity due to the lack of abnormally strong subtropical ridging typical seen in La Niña summers.

With the Kelvin wave delaying the onset of La Niña, neutral ENSO conditions are expected through the end of July (see section 3). Previous warm AMO seasons that followed winter El Niño conditions and had neutral ENSO conditions during June-July include 1966, 1995, 2003, and 2005. All four of these years advertised above average tropical cyclone activity before August, with no fewer than 3 named storms and 2 hurricanes. A similar evolution of ENSO has been witnessed in the first half of 2007, thus above average June-July activity is likely. However, other parameters suggest that observed activity will remain below that of several ENSO analogs. First, the strong ridging that has extended through the Gulf of Mexico and into the west Atlantic this past spring argues against formation in the Gulf of Mexico or west Caribbean until later in the season. Second, the AMO was very strong in summer 2005 and also slightly stronger in 1966 and 1995 than it is at present. The extremely warm tropical Atlantic SSTAs in 2005 helped fuel the record-breaking June-July activity. On the other hand, the AMO in summer 2003 was closer to neutral and more comparable to current trends. It is no surprise that 2003 had the least amount of June-July activity in the four-year sample. Therefore, 2-3 named storms and 0-1 hurricanes are forecast to develop before August. These developments will likely be confined to the Mean Development Region or west Atlantic.

August-September

Atlantic Basin tropical cyclone activity tends to experience a fairly sharp increase during the month of August, particularly after August 15. August and September are by far the most active months of the season, with the climatological peak of activity being early to mid September. In nearly all cases, an above average hurricane season equates to above average activity during August-September.

The establishment of a worthwhile August-September tropical cyclone forecast method was not as arduous to develop as the June-July formula. First, the warm (cool) AMO signals above (below) normal activity. Second, summer La Niña (El Niño) is the most enhancing (suppressing) phase of ENSO, thus matching the traditional ENSO-tropical cyclone variability relationship. The primary difference in bimonthly forecast methodology is the elimination of winter ENSO as a parameter. Additional statistics developed in recent months indicate that any residual winter ENSO effects become too minimal to have any significant influence on Atlantic tropical cyclone activity by August and September.

The climatological peak of hurricane season 2007 is expected to underscore the effects of a moderately warm AMO combined with La Niña conditions that will have already been present for at least a month. Accordingly, more emphasis has been placed on previous warm AMO and summer La Niña seasons: 1950, 1955, 1961, 1988, 1995, 1998, and 1999. All (7/7) seasons with such conditions produced between 7 and 10 named storms during August-September, which are above the climatological average of 6.5 named storms. Furthermore, all of the aforesaid years advertised average to well above average activity in the Mean Development Region, and most Mean Development Region formations occur within August-September. It has already been concluded that above normal Mean Development Region activity will be observed this year. However, the bimonthly August-September period of 2007 is not forecast to approach the upper confines of the 7-10 named storm range provided by those years for two primary reasons. First, although activity east of the Lesser Antilles will be above normal, it should not be as active as 1995. Additionally, the mid to upper-level geopotential height pattern is not conducive for tropical cyclogenesis in each of the remaining four regions (see section 6). An estimated 7-8 named storms, 5-6 hurricanes, and 2 major hurricanes are forecast to develop during the bimonthly period of August-September, with most formations occurring in the Mean Development Region.

October-November

As October approaches, a noticeable decline in Atlantic Basin tropical cyclone activity is typically observed. On average, 2-3 named storms form during October-November, which is far less than August-September, but slightly more than what is typically monitored in June-July. However, in rare cases more activity can occur during October-November than the climatological peak. This scenario last materialized in 2005. Otherwise, several of the most intense hurricanes ever observed in the Atlantic Basin have formed during the October-November period. In short, the Atlantic hurricane season is often far from cessation by late September.

The October-November tropical cyclone forecast methodology is nearly the same as that used for the bimonthly period of August-September. The forecast is highly dependent on the AMO, summer and fall ENSO, and springtime mid to upper-level geopotential heights over the Atlantic Basin and North America. Warm AMO and fall La Niña conditions have yielded anywhere from 2-6 named storms in past bimonthly October-November periods. However, the use of the already given geopotential height pattern should help lower and narrow that range quite a bit. For example, 1950 is one of eight warm AMO and fall La Niña analogs. October 1950 featured 6 tropical cyclones, but 3 of which originated in the Gulf of Mexico. This year, it is unlikely that even one named storm will develop in the Gulf during October for several reasons (see section 6), one of which being the geopotential height pattern. Tropical cyclones simply are not likely to form in the areas where they occurred during analog seasons with more than 3 October-November tropical cyclones. On the other hand, the west Caribbean and Mean Development Region will be primed to support at least one tropical cyclone development, the former likely being a major hurricane. Therefore, 2-3 named storms, 1-2 hurricanes, and 1 major hurricane are forecast to develop during the bimonthly period of October-November.

8. Landfall Activity By Coastal Areas

The concept of correctly forecasting tropical cyclone landfall distribution months in advance is and should be the long-term goal of seasonal forecasting. Seasonal forecast boundaries must be tested in order for such forecasts to become more accurate and useful. Otherwise, seasonal hurricane forecasts will continue to be of little to no value to the general public. In short, many researchers insist that the synoptic steering pattern and consequential tropical cyclone landfalls cannot be forecast months in advance. To the contrary, evaluation of the synoptic springtime pattern in combination with analysis of parameters known to influence Atlantic Basin hurricane activity can yield significant skill in seasonal landfall forecasting. Since the landfall forecasts issued in 2006 were a great success, it has been decided that similar landfall forecasts will be issued for a fifth year.

The method used to generate regional landfall forecasts is essentially unchanged since 2006. Springtime mid-level geopotential heights across North America, the Atlantic Basin, and adjacent regions were analyzed. Additionally, the newly developed four-phase SNA configurations, springtime NAO, AMO, and ENSO are being given more weight this year.

Venezuela and Leeward Antilles

One typically does not think of this area being directly affected by tropical cyclones. But in recent years, a number of notable hurricanes have passed close enough to the Leeward Antilles and Venezuela to cause minor damage and indirect fatalities. Hurricanes Ivan and Emily in 2004 and 2005, respectively, are two noteworthy examples. No such low-latitude tracking tropical cyclones are expected this season for two primary reasons.

First, there are quite a few notable differences between the overall setup during the aforementioned seasons and 2007. In short, the onset of El Niño conditions in 2004 delayed tropical cyclone formation in the Mean Development Region, thus allowing for more storms to develop in close proximity to the Caribbean Sea. The ridging pattern over the central Atlantic was also more supportive of westerly tracking tropical cyclones. In 2005, it was the negative spring NAO that delayed formation in the Mean Development Region. The ridging pattern also favored westerly tracking tropical cyclones for a second consecutive year. This year, nearly all parameters known to affect activity in the deep tropical Atlantic are favorable, thus corresponding to formations farther east and away from the Caribbean Sea. East Atlantic-originating tropical cyclones are naturally less likely to effect the Caribbean since there is more time and opportunity for them to be steered north by atmospheric troughs in conjunction with the Coriolis effect.

Second, Phase 2 of SNA configuration combined with a positive NAO directly argues against low-latitude tropical cyclone tracks across the south Caribbean. Had the SNA met Phase 1 criteria, south Caribbean landfalls would still be a possibility despite the positive NAO. SNA Phase 1 criteria was not met because of an absence of dominant ridging along 20ºN between 60-70ºW. Phase 2 portrays the 2007 setup more accurately with ridging present over the central Atlantic and troughing located beyond 60ºW. No tropical cyclones are forecast to strike Venezuela or the Leeward Antilles.

Nicaragua

Landfalls along the Nicaraguan coastline are not common but certainly happen. The last storm was Hurricane Beta in 2005. However, the region should be spared tropical cyclone landfalls in 2007 for a variety of reasons. First, a large mid to upper-level weakness located near 60ºW will be the focal point of recurvature for all tropical cyclones that form east of the Caribbean. Second, Phase 2 of the SNA configuration combined with a positive NAO directly argues against low-latitude tropical cyclone tracks across the lower Caribbean Sea. Third, the combination of La Niña, warm AMO, and positive springtime NAO conditions argue against in-situ east Caribbean Sea formation. With all that said, it is highly unlikely that any tropical cyclones will pass west of 75ºW while still in the Caribbean Sea.

The only potential remaining source for Nicaragua tropical cyclone threats is in-situ west Caribbean Sea development. Even then, the leading parameters argue against multiple west Caribbean Sea formations, especially preceding October. However, one significant late-season tropical cyclone is likely. Springtime pattern tendencies indicate more of a threat to Honduras and the Yucatán Peninsula than points further south. No tropical cyclones are forecast to directly impact Nicaragua.

Honduras and Yucatán Peninsula

This region was hit hard in 2005 by major Hurricanes Emily and Wilma. After a break in 2006, it appears the Yucatán Peninsula and Honduras face yet another major hurricane this year. As aforementioned, no Mean Development Region or east Caribbean Sea-originating tropical cyclones are forecast to enter the west Caribbean Sea. Moreover, only one tropical cyclone, albeit a major hurricane, is expected to develop in the west Caribbean Sea during the latter third of the season (see section 6).

Once it was determined that a late season major hurricane would likely be the highlight of west Caribbean activity, the springtime geopotential height patterns preceding seasons that featured such storms were analyzed. Analogous geopotential height composites based on the following four steering scenarios were then created: Central America landfall followed by dissipation, Central America landfall followed by recurvature into Florida, recurvature resulting in a Florida landfall, and recurvature east of Florida. Variance in the patterns among individual years within all four composites yield only minute variance, thus increasing confidence in the utilization of spring geopotential height composites for this forecast. Moreover, the geopotential height patterns defined by each composite logically match with what one would expect given the observed hurricane tracks among the composite years.

The anomalous ridge over the southeast United States and weakness along 60ºW observed in spring 2007 best match the geopotential height pattern defined by the first composite. All three seasons (1961, 1995, 2000) used in the first composite featured a late-season, major hurricane that originated in the west Caribbean and struck the Yucatán and/or Honduras. Furthermore, all three of those hurricanes were guided by anomalous ridging to the north. The analogous weaknesses located near 60ºW apparently had little influence on steering as they were too weak and far east. Therefore, recurvature over Florida or points east is highly unlikely. With that said, one major hurricane is forecast to make landfall in Honduras or the Yucatán Peninsula. This projected storm will originate in the west Caribbean Sea during the latter half of the season.

Mexico

The Mexican Gulf coast was hard-hit by Hurricanes Emily and Stan in 2005, but fortunately received a break in 2006 much like the Yucatán Peninsula. The SNA configuration and unique spring geopotential height pattern have been evaluated to gauge the tropical cyclone threat posed this season. Since no tropical cyclones are anticipated to enter the Gulf of Mexico (see section 6) from the Mean Development Region, west Atlantic, or east Caribbean Sea, the threat has been reduced to in-situ west Caribbean and Gulf of Mexico formation. Furthermore, only one tropical cyclone, albeit strong, is expected to originate in the west Caribbean. While the projected tropical cyclone is most likely to strike the Yucatán Peninsula or Honduras, a secondary landfall along the Mexican Gulf coast is not a sure bet. Hurricanes Hattie and Roxanne in 1961 and 1995, respectively, are examples of late season major hurricanes that struck the Yucatán and later dissipated over the Bay of Campeche. On the other hand, Keith in 2000 hit the Mexican state of Verecruz as a category 1 hurricane. Although it is unlikely that the west Caribbean major hurricane will restrengthen into a major hurricane in the Gulf of Mexico, there is the possibility of a secondary weaker landfall along the Mexican Gulf coast.

Finally, given that the spring geopotential heights over the Gulf of Mexico and adjacent Caribbean and North American regions bear resemblance to Phase 4 SNA years, no more than one tropical cyclone is forecast to form in the Gulf of Mexico. However, the lack of any troughing immediately north or northeast of the Gulf of Mexico argues against recurvature into the United States Gulf coast. Rather, the abnormal degree of ridging that has been in place over the southeast United States supports the idea that any Gulf-originating tropical cyclones will head westward into Mexico. Therefore, the Mexican Gulf coast has a high risk of being impacted by 1-2 named storms and 0-1 hurricanes, all stemming from in-situ development in the west Caribbean Sea and Gulf of Mexico.

Texas

While Jefferson and Orange counties were significantly impacted by Hurricane Rita in 2005, no tropical cyclone has made a direct landfall in Texas since 2003. This streak should continue through 2007. Climatologically, springtime troughs or regions of low geopotential heights over Texas and north Mexico have preceded tropical cyclone landfalls along the Texas coastline. With that said, the 2007 spring pattern featured strong ridging over the central United States, northern Mexico, and Gulf of Mexico. Originally, it was theorized that the anomalously strong easterly flow associated with the ridging over the Gulf of Mexico could still allow a tropical cyclone to hit Texas. However, three years with analogous spring geopotential heights (1967, 1990, and 2000) were considered. During those years, all tropical cyclones that formed in the southwest Gulf of Mexico or west Caribbean Sea continued westward and struck Mexico, well south of Texas. Since the spring ridge extends even further south this year, and geopotential heights in the Caribbean Sea have been neutral to slightly above average, the few tropical cyclones that enter or originate in the Gulf of Mexico will almost certainly be blocked from striking Texas. Accordingly, no tropical cyclones are forecast to hit coastal Texas this season.

Louisiana, Mississippi, and Alabama

It is a significant understatement to say the coastline from Louisiana through the Big Bend of Florida was hard-hit in 2005. This region was forever changed from Hurricane Katrina, not to mention the barrage of three other hurricanes. All in all, the recovery process will take several more years, not months, and even then some areas will never be the same. All one can do is hope that mother nature spares the central Gulf coast from additional landfalls in the near future. Subsequently, one of the leading questions heading into the 2007 hurricane season is whether a tropical cyclone is likely to threaten the central Gulf coast. The 2007 outlook is encouraging for interests in this area.

The upper air pattern over the central Gulf coast has behaved similarly to that observed in 2006. Unusually strong high pressure dominated the southeast and central United States for the better half of spring 2007. Analogous patterns have kept all tropical cyclones away from the central Gulf coast in the past. The central Atlantic weakness should prevent any tropical cyclones from entering the southeast Gulf of Mexico from the Bahamas. Meanwhile, the aforementioned ridging pattern over the southeast should keep any Gulf of Mexico or west Caribbean-originating storms south and west of the central Gulf coast. Furthermore, the SNA configuration suggests that Gulf of Mexico tropical cyclone activity as a whole will be below average. Therefore, no tropical cyclones are forecast to impact the central Gulf coast.

West Florida

The west coast of Florida was recently struck by major Hurricanes Charley and Wilma in 2004 and 2005, respectively. Tropical storm activity was also noted along the coastline in 2006. The risk of tropical cyclone landfalls in West Florida has been deemed to be low this year.

While the ridging pattern over the central Gulf coast does resemble that observed in 2006, there are notable differences elsewhere that pertain to Florida peninsula threats. Last season, the southeast United States ridge, in tandem with a massive central Atlantic trough and a developing El Niño, supported tropical cyclone recurvature over the southeast Gulf of Mexico. This year, the ridge has routinely expanded beyond the East coast, thus making the central Atlantic trough less of a recurvature mechanism for west Caribbean and Gulf of Mexico tropical cyclones. Close comparisons between the spring patterns of 1995, 2000, and 2007 were made since all three shared basic pattern similarities. However, the central Atlantic trough in 1995 and 2000 extended much further south and west than what has been observed this past spring. The trough, combined with low geopotential heights within the Caribbean, resulted in a pattern that enabled tropical cyclones to curve into west Florida during those years. On the other hand, 1961 and 1967 had a more similar ridge-trough orientation and no west Florida landfalls were observed. Finally, the intensity of the ridging noted over the Florida peninsula, in combination with developing La Niña conditions, argues for more westerly tracks of any tropical cyclones that form in the west Caribbean or Gulf of Mexico. Thus, no tropical cyclones are forecast to directly hit the west coast of Florida.

East Florida

After experiencing three hurricane landfalls in 2004-2005, not including a brush from Hurricane Rita, the east coast of Florida was largely spared in 2006. Fortunately, the break for the east coast of Florida is expected to continue through 2007. A few correlations have been noted regarding East Florida landfalls. First, years with positive spring NAO combined with high (low) geopotential heights south of Greenland usually feature increased (decreased) east Florida tropical cyclone activity. Second, years with winter El Niño (La Niña) conditions prior to the hurricane season also average more (less) east Florida landfalls, especially during positive or negative (neutral) spring NAO. While the physical mechanisms responsible for these statistical correlations remain unexplained at the present time, they are worth taking into consideration. The geopotential heights south of Greenland this past spring have been slightly below average. On the other hand, this past winter featured an El Niño, and this past spring was characterized by a positive NAO. The contradictory signals forced a closer examination of the overall Atlantic Basin pattern.

As aforementioned, this past spring featured a weakness centered between strong ridging over the continental United States and northeast Atlantic. An analogous feature was observed in 1995, a year that also had a winter El Niño, spring positive NAO, and slightly below average geopotential heights south of Greenland. All of the tropical cyclones that developed in the Mean Development Region in 1995 recurved into the central Atlantic weakness. Likewise, all Mean Development Region or central Atlantic-originating tropical cyclones should recurve east of the Florida peninsula in 2007. The only evident differential between 1995 and 2007 that pertains to east Florida is the geopotential height pattern over the west Atlantic, which has been more positive this year. Stronger geopotential heights in tandem with developing La Niña conditions do not support such west Atlantic developments that occurred in 1995. Any in-situ west Atlantic tropical cyclogenesis in 2007 is most likely to occur well east of Florida and the Bahamas. Any formation east of the Bahamas is more likely to recurve out to sea rather than veer into Florida given the spring pattern. Therefore, no tropical cyclones are forecast to hit the east coast of Florida.

Georgia, South Carolina, and North Carolina

The Carolinas are certainly no stranger to tropical cyclones. The Outer Banks of North Carolina jut outward and are thus especially prone to hurricane strikes. However, this region will largely escape tropical cyclone activity in 2007. First, unusually strong ridging over the continental United States will prevent any Gulf of Mexico or west Caribbean originating tropical cyclones from recurving through Florida and the East coast. Second, the eastern periphery of the ridging over the East coast, in tandem with warm AMO and developing La Niña conditions, does not support coastal tropical cyclogenesis. Any in-situ west Atlantic tropical cyclone development is most likely to occur well south and east of Georgia and the Carolinas. Finally, a geopotential height weakness centered between two high pressure systems, one over the continental United States and the other over the northeast Atlantic, should permit all west Atlantic and Mean Development Region-originating tropical cyclones to recurve near 60ºW, well east of the United States East coast. Thus, no tropical cyclones are forecast to make landfall along the Georgia, South Carolina, or North Carolina coastlines.

Mid-Atlantic and Northeast United States

One may not consider states north of the Carolinas to be frequently hit by tropical cyclones, but the region has certainly seen its fair share of destructive landfalls. Fortunately, no such landfalls should occur in 2007. The springtime North American geopotential height configuration suggests that any tropical cyclones that do form in the west Atlantic or Mean Development Region will recurve well to the east near 60ºW.

Furthermore, winter El Niño (La Niña) conditions preceding hurricane season average less (more) Mean Development Region-originating tropical cyclones that impact the Northeast states, especially during neutral (extreme) spring NAO years. In fact, all seven seasons that featured such tracks followed winter neutral or cool ENSO conditions and a moderate spring NAO. It is interesting to note that the opposite is observed with east Florida landfalls, which are more frequent in seasons following warm ENSO winters and extreme spring NAO values. This might suggest that the factors utilized in this study have a lag influence on tropical cyclone steering patterns which either forces storms to curve northward into the Northeast states or continue into Florida. Another statistic worth pointing out is that west Atlantic-developing tropical cyclones that hit the Northeast states were all in seasons with an El Niño, cool AMO, or both. Since neither will be present in 2007, it is unlikely that there will be many formations in the west Atlantic, much less one making landfall in the Northeast states. Accordingly, no tropical cyclones are expected to hit the Mid-Atlantic or Northeast states this season.

Atlantic Canada

Contrary to popular belief, the Atlantic coast of Canada is no stranger to tropical cyclones, with the most notable being Hurricane Juan of 2003 that devastated Halifax, Nova Scotia. The mean trough position during August-September should be located near 60ºW, which runs perpendicular to the easternmost half of the Atlantic Canada. With 5-6 hurricanes forecast to recurve along that general longitude, it is reasonable to presume that at least a few tropical cyclones will threaten or bypass the coastline this year. Moreover, tropical cyclones that develop in the west or northeast Atlantic are likely to take similar paths. This season, Newfoundland has a higher risk of tropical cyclone brushes and possibly even 1-2 landfalls than the maritime provinces of New Brunswick, Nova Scotia, and Prince Edward Island. Most or all tracks should remain south and just east of the maritime provinces.

Azores

Tropical cyclones occasionally hit the Azores. In fact, category 1 Hurricane Gordon passed through the islands in 2006. A similarly strong tropical cyclone is unlikely to impact the Azores this year. This past spring has featured a strong mid-level ridge centered in close proximity to the islands that extends west to 55-60ºW. Thus, the multiple tropical cyclones that form in the Mean Development Region are expected to recurve west of 40ºW, a position far enough west to avoid the Azores. Moreover, the ridge will prohibit tropical cyclones from forming near the Azores. However, 1-2 named storms are expected to form between 40-60ºW in the northeast Atlantic. The recurvature trajectories of such storms are more difficult to forecast, thus some impact from these storms cannot be ruled out.

Cape Verde

Although Cape Verde is often impacted by developing tropical depressions, actual named storm hits are uncommon since the time of passage over water from Africa is limited. However, the few stronger systems that have hit Cape Verde resulted in significant damage. With a strong ridge in place over the east Atlantic this past spring, such a direct hit appears unlikely this year. Thus, any early tropical cyclone development off the west coast of Africa is expected to occur south of Cape Verde.

Puerto Rico, Leeward Islands, and Windward Islands

Following the 1998 and 1999 hurricane seasons, Puerto Rico and the Leeward Islands have managed to escape a direct hit from a significant hurricane. Unfortunately, there are indications that the eight-year streak of no landfalls is about to be shattered. There is a high risk of 1-2 significant tropical cyclone landfalls in Puerto Rico and the Leeward Islands.

Two ingredients are necessary for this area to be considered a high risk zone: favorable conditions in the Mean Development Region and a steering mechanism that will keep any Mean Development Region-originating tropical cyclones on a westward heading toward the islands. Obviously, the Mean Development Region is the primary source region of tropical cyclones that impact the northeast Caribbean. This year, the area is expected to be highly favorable for tropical cyclogenesis. A combination of warm AMO, La Niña, and positive springtime NAO conditions favors a strong Cape Verde hurricane season, with 7-8 named storms, 4-5 hurricanes, and 1-2 major hurricanes forecast to originate in the Mean Development Region. More importantly, stronger than normal mid to upper-level ridging has dominated the subtropical Atlantic in recent months. The ridging often extends as far west as 60ºW, which is where an overall weakness in the synoptic pattern has taken shape. The majority of tropical cyclones that do form in the Mean Development Region will harmlessly recurve northeast of the island chain. However, the probability that all 7-8 tropical cyclones will recurve east of the islands is very low given the degree of ridging that has been in place. Furthermore, the 1-2 tropical cyclones that continue westward into the northeast Caribbean while underneath the large subtropical ridge will likely be intense due to synoptic reasons.

The one bit of good news is that all Mean Development Region-originating tropical cyclones should remain north and east of the Windward Islands. The degree of ridging along 20ºN decreases significantly by 60ºW. Thus, all tropical cyclones that threaten the east Caribbean should begin to recurve no later than 55-60ºW. Moreover, all parameters indicate that tropical cyclone formation immediately east of the Windward Islands is unlikely. Thus, no tropical cyclone landfalls on the Windward Islands are expected.

Bahamas and Turks and Caicos Islands

Tropical cyclones frequently impact the Bahamas and Turks and Caicos Islands, but a number of parameters argue against a direct hit in 2007. First, a weakness centered between two high pressure systems, one over the continental United States and the other over the northeast Atlantic, should permit all west Atlantic and Mean Development Region-originating tropical cyclones to recurve east of the Bahamas and Turks and Caicos Islands. Such tracks are also supported by a combination of positive springtime NAO, warm AMO, and La Niña conditions. Second, no tropical cyclones are forecast to originate in the east Caribbean Sea (see section 6). Third, the anomalous ridging centered over the continental United States should prevent any late-season, west Caribbean tropical cyclones from recurving into Cuba and the Bahamas. Fourth, the eastern periphery of the ridge in tandem with La Niña and warm AMO conditions will hinder west Atlantic development. Finally, the pattern also suggests that any in-situ west Atlantic tropical cyclones would likely recurve away from the Bahamas and Turks and Caicos Islands. No tropical cyclones are forecast to directly impact this region.

Cayman Islands, Cuba, Jamaica and Hispaniola

Tropical cyclones that have hit these islands in the past have resulted in significant damage, but it looks as if the general area will escape the wrath of the 2007 hurricane season despite being located directly between the two “highest risk” regions of the Atlantic Basin. First, a weakness centered between two high pressure systems, one over the continental United States and the other over the northeast Atlantic, should permit all west Atlantic and Mean Development Region-originating tropical cyclones to recurve over or east of Puerto Rico, thus sparing Hispaniola and points westward from a direct landfall. Second, the combination of La Niña, warm AMO, and positive springtime NAO conditions argue against in-situ east Caribbean Sea formation. Finally, any late season tropical cyclone that may form in the west Caribbean Sea is likely to continue westward into Honduras or the Yucatán Peninsula rather than recurving due to the abnormal ridging noted over the southeast United States last spring. No tropical cyclones are forecast to directly impact the Cayman Islands, Cuba, Jamaica, and Hispaniola.

Bermuda

Located in the middle of the Atlantic Basin, Bermuda is often brushed by tropical cyclones. Because of its small size, however, direct landfalls do not occur often. In 2007, the mean trough position will put Bermuda in danger of getting sideswiped by several recurving hurricanes that originated in the Mean Development Region or west Atlantic. It is difficult to say if any will directly hit the island, but residents and tourists should be prepared to deal with multiple hurricane threats during August and September.

9. Conclusion

A moderately warm AMO combined with La Niña conditions should allow the upswing in Atlantic Basin tropical cyclone activity that began in 1995 to continue in 2007. Above average activity is forecast in the Mean Development Region, with at least one major hurricane striking the northeast Caribbean before recurving into the west Atlantic. A weakness between two intense ridges over the east Atlantic and continental United States will act as a protective barrier of tropical cyclones for the United States East coast. No tropical cyclones are expected to undercut the weakness and continue westward through the Caribbean Sea. Meanwhile, ridging over the continental United States should keep any Gulf or Caribbean-originating tropical cyclones away from the United States Gulf coast. However, the Mexican Gulf coast and east shore of the Yucatán Peninsula run a risk of landfalls stemming from homegrown tropical cyclone activity in the southwest Gulf of Mexico and west Caribbean Sea. The featured homegrown development in the west Caribbean Sea is expected to be a late-season major hurricane. Finally, the forecast total number of tropical cyclones in June-November is presented below. While the 2007 season is expected to be somewhat above average, the level of activity should be far less than that observed in 2004 or 2005.

 

IWIC 2007 Atlantic Basin Hurricane Season Forecast
Off-season formations not included.

Parameter
2007 Forecast
Long-Term Average
Named Storms
13
11
Hurricanes
8
6
Major Hurricanes
3
2

Regardless of seasonal expectations, interests in hurricane-prone areas should always be prepared for a tropical cyclone landfall. Even if 2007 unexpectedly features below normal tropical cyclone activity, it would only take one intense landfalling hurricane to make the season a devastating one. Such a scenario occurred 15 years ago. All measures of tropical cyclone activity were below normal in 1992. However, it was the year that category 5 Hurricane Andrew slammed south Florida and Louisiana, which resulted in 65 fatalities and over 30 billion dollars of damage.

No changes will be made to the 2007 seasonal forecast over the course of the season, though updates will be posted within the IWIC daily tropical weather discussions. A post-review of the 2007 season will be underway by December. Such timing will enable the forecasters to analyze how well the latest methodology fared, and then make adjustments for 2008 if necessary. Preliminary research on the 2008 Atlantic Basin hurricane season will ensue January.

Daily Tropical Weather Discussion

IWIC Worldwide Tropical Weather Discussion – June 22 2007 – 01:30 UTC

There’s no change to our thinking in regards to the tropical wave over the western Caribbean Sea. There are no longer any models hinting at the possibility of tropical cyclone formation once the wave enters the southwest Gulf of Mexico. The lack of aggression is due to the wave’s proximity to land along with it’s interaction with upper level wind shear. A midlevel circulation did become apparent on satellite imagery in the late afternoon hours, but it is unlikely to persist due to the aforementioned reasons. This system will bring additional moisture to Texas and Louisiana, with the main axis moving inland over mainland Mexico early next week. The only other feature worth mentioning in the Atlantic basin is the low over Jacksonville. No development is expected as it is expected to remain over land before it becomes absorbed by an approaching trough.

June 21 2007 – 01:30 UTC

The tropical Atlantic remains quiet, but there are online rumblings over the possibility of west Gulf development in about five days. The potential source of tropical cyclone formation is the tropical wave currently located in the southwest Caribbean. The 00Z and 12Z runs of the GFS and ECMWF models indicated that this feature would cross Central America and eventually enter the central or southwest Gulf of Mexico. The ECMWF depicted a suspect broad low in the Gulf before moving into Texas or Mexico. The GFS was more bullish, showing almost the equivalent of a minimal tropical cyclone heading north or northwest toward the upper Texas coast and southwest Louisiana.

The aggressive GFS runs should likely be disregarded. The model still appears to be suffering from convective feedback. The convective feedback problem is responsible for the progged development of a surface low along the northern extent of the wave axis while over the central Gulf in a few days. This is why the GFS is too aggressive and too far north. The GFS assumes the low will be strong enough and far enough north that it will be drawn into the US Gulf Coast by a minor mid-level weakness over the southeast.

The rest of the models aren’t nearly as aggressive. The Canadian model, which is often way too bullish, is showing little in the way of any surface low development in the gulf. The NOGAPS and UKMET clearly show the wave remaining confined to the extreme southern Gulf and Bay of Campeche before moving into mainland Mexico. The ECMWF, which wasn’t overly aggressive to begin with, shows the same general scenario as the NOGAPS and UKMET.

Bottom line: The chance of Gulf development appears to be very low. If development were to occur, it would likely take place in the extreme southwest Gulf or Bay of Campeche. One of the few reasons why development cannot be ruled out completely is due to the fact that the global models struggled to pick up on the rapid formations in this area in 2005. Any tropical cyclone that does form would likely head into mainland Mexico due to the wave’s low latitude once it enters the Gulf and its relative lack of intensity.

June 10 2007 – 23:30 UTC

There’s not much to add from yesterday evening’s discussion. The tropical wave in the eastern Atlantic is weakening and tropical cyclone formation remains unlikely. Elsewhere, disorganized convection remains spread out across the Caribbean, but upper level conditions will remain unfavorable for tropical development. Also, the upper low near the Yucatan peninsula will quietly drift westward into Mexico or southern Texas with no development. So all is quiet this evening.

June 10 2007 – 02:00 UTC

An impressive tropical wave, at least by early season standards, rolled off the African coast earlier today. The wave is well-defined in the low to mid levels as a result of favorable winds aloft. QuikSCAT imagery depicts a strongly inverted wave axis, with southwest winds converging toward a weak low center. There does not appear to be a completely closed off surface circulation. A large upper level high extends from central Africa westward to the Cape Verde islands. The longwave trough located between 40-50ºW is having little influence on the wave. But that is likely to change over the next several days. Although the wave is currently well-defined, all model guidance does suggest that it will outrun the favorable upper level conditions that are present over the eastern Atlantic. Once along the western periphery of the high, southwest winds ahead of the trough will increase over the wave axis, thus resulting in less organization.

The projected result of the shear on the wave axis is also apparent when one compares the low and mid level vorticity maps. For example, the trough is not as deep in the low levels. With that said, the wave will continue to be guided nearly due west toward the Lesser Antilles under a strong surface ridge. However, the mid level energy associated with the wave will gradually take a more northerly component due to the mid level weakness over the central Atlantic. In other words, the shear should be strong enough to keep this wave from remaining vertically stacked, thus making tropical cyclone formation unlikely.

The wave should be monitored for some signs of organization while conditions remain somewhat favorable over the next few days. However, if all of the available model guidance is correct, any short term organization will become irrelevant as a strong trough over the central Atlantic begins to interact with the wave by the middle of next week. Of course this is subject to change, but that is how things look as of this evening. It should also be noted it’s very early for development in the far east Atlantic, but several strong waves have already exited Africa this season. Similar observations are made on numerous forums nearly every year, but they may hold merit this year. It’s especially interesting since we anticipate a strong Cape Verde season.

The rest of the Atlantic basin is generally quiet. A large area of convection developed in the southwest Caribbean earlier, but upper winds should remain unfavorable for tropical cyclone formation.

June 09 2007 – 01:30 UTC

The return of the discussions are eight days late, but better late than never right? Due to time constraints, the discussions will likely be short and more to the point until a system becomes of decent interest in the Atlantic basin.

a tropical wave is located near the Lesser Antilles, but there are no signs of organization. Shear remains moderate to strong. All dynamical model guidance shows the wave continuing westward through the Caribbean with little sign of additional orginization. In the southwest Atlantic, an upper level low is generating isolated convection, but this system is not tropical in nature.