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Gulf of Mexico Distubance--30% Chance to Develop; TD 9 Struggling; 95L May Develop

By: Jeff Masters 2:35 PM GMT on September 17, 2015

An area of disturbed weather has developed along the boundary of an old front in the Eastern Gulf of Mexico off the coast of Florida, and is bringing heavy rains to portions of the Florida Peninsula, where 2 - 3" of rain are expected over the next few days. The disturbance is under high wind shear of 20 - 30 knots, and it unlikely to develop in the Gulf. Satellite loops on Thursday morning showed little signs of rotation, and only a modest area of heavy thunderstorms. However, the disturbance is moving to the northeast, and will emerge over the waters off the coast of South Carolina by Saturday, when the GFS and European models predict that wind shear may fall to the moderate range, 15 - 20 knots. This drop in shear may be enough to allow some development. None of our three reliable models for predicting tropical cyclone genesis are showing development of a tropical depression, though. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 30%, respectively.

Figure 1. Latest satellite image of the Gulf of Mexico, courtesy of NOAA.

Tropical Depression Nine no big deal
Tropical Depression Nine continues to chug to the northwest at 6 mph over the open Atlantic, well away from any land areas. Satellite images show that high wind shear has exposed the surface circulation of TD 9 to view, and the storm has lost almost all of its heavy thunderstorms. The long-range fate of TD 9 is complicated to predict, since the storm will interact with Invest 95L to its southeast. In any case, TD 9 is very unlikely to threaten any land areas, and will be of most concern to trans-oceanic sailors and fish.

Figure 2. Latest satellite image of TD 9.

Invest 95L may develop
A tropical wave (Invest 95L) located about 600 miles southwest of the Cape Verde islands on Thursday morning was moving west-northwestwards at about 10 - 15 mph. Satellite images showed little change to the wave on Thursday morning; 95L has pretty of spin, but dry air is keeping heavy thunderstorm activity meager. Conditions are favorable for development, with wind shear a light 5 - 10 knots, ocean temperatures at 28°C (83°F), and only a modest amount of dry air from the Saharan Air Layer lying to the north of the disturbance. Our three reliable models for predicting tropical cyclone genesis, the UKMET, European, and GFS models, forecasted in their 00Z Thursday runs that 95L would develop into a tropical depression by Monday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 95L 2-day and 5-day odds of development of 70% and 80%, respectively. 95L will turn more to the north over the Central Atlantic over the weekend, and it unlikely to ever pose a threat to the Caribbean or North American coast.

Figure 3. Latest satellite image of 95L.

I'll have a new post by noon EDT, when the results of NOAA's monthly report on August global temperatures will be available.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.