Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 1:50 PM GMT on August 13, 2012
The remains of Tropical Depression Seven are headed westward at 20 mph across the Central Caribbean, and will bring heavy rain to Jamaica and Southwest Haiti today. Satellite loops show that ex-TD 7 has only a modest amount of heavy thunderstorms, with no signs of any organization. High wind shear of 15 - 25 knots should prevent the system from regenerating today. Wind shear will fall to the low range over the disturbance on Tuesday and Wednesday, but there is not going to be enough time for ex-TD 7 to develop before it moves inland over the Yucatan Peninsula on Wednesday. None of the reliable models forecasts that TD 7 will regenerate, and in their 8 am Tropical Weather Outlook, NHC gave ex-TD 7 a 10% chance of becoming a tropical depression by Wednesday morning.
Figure 1. Morning satellite image of 93L over the Central Atlantic.
A large tropical wave (Invest 93L) is located in the Central Atlantic about 1200 miles west-northwest of the Cape Verde Islands. Satellite loops show a pronounced spin to the atmosphere at mid levels, but little in the way of heavy thunderstorm activity. The latest Saharan Air Layer Analysis from the University of Wisconsin shows that 93L is surrounded by a large area of dry air from the Sahara, which has infiltrated into the storm. This dry air will be a significant impediment to development, as the 8 am EDT run of the SHIPS model predicts that mid-levels of the atmosphere will remain very dry during the next four days. The storm is expected to move west-northwest and then north, recurving well to the east of Bermuda. By Saturday, as 93L is headed northeastwards towards the Azores Islands, the disturbance will find a moister environment, and the GFS model predicts development into a tropical storm will occur. None of the other reliable models predict development, but residents of the Azores Islands should keep an eye on 93L. In their 8 am Tropical Weather Outlook, NHC gave 93L a 10% chance of becoming a tropical depression by Wednesday morning.
Another area to watch this weekend will be the Gulf of Mexico, where a fall-like cold front is expected to stall out. Though no models are showing tropical storm development will occur, wind shear is predicted to be low to moderate this weekend, and cold fronts stalled out over the Gulf of Mexico often serve as the seed for tropical storms.
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