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.

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