TD 5 strugging
Jeff Masters

2:04 PM GMT on August 02, 2012

A disheveled Tropical Depression Five is clinging to life in the face of stiff wind shear and dry air, as the storm heads towards the Lesser Antilles Islands with a forward speed of 20 mph. The depression is very ragged looking on visible satellite loops. The depression has only a small area of heavy thunderstorms, which are on the south side of the center due to high wind shear and dry air on the northern side of the storm. Wind shear over TD 5 is at the moderate level, 15 - 20 knots. Water vapor satellite loops show that TD 5 is at the southern edge of a large area of dry air. Wind shear due to strong upper level winds from the west is driving this dry air into the core of the storm, disrupting it. The first Air Force hurricane hunter aircraft will investigate TD 5 Thursday afternoon to give us a better idea of its strength.


Figure 1. Morning satellite image of TD 5.

Forecast for TD 5
TD 5's west to west-northwest motion should bring its outer rain bands to Barbados early Friday morning, and high winds and heavy rain will spread over the rest of the Windward Islands by Friday afternoon. Since wind shear will be higher on the storm's north side, I expect the heaviest weather will be on the south side of TD 5, over the Windward Islands. Wind shear is expected to remain moderate, 10 - 20 knots, through Friday, according to the 8 am EDT run of the SHIPS model. However, the reliable ECMWF model predicts higher shear on Friday and Saturday, which could tear TD 5 apart. A number of our reliable computer models predict TD 5 will not survive its passage through the islands this weekend. However, most of the models agree that once TD 5 (or its remnants) pass enter the Central Caribbean on Monday, wind shear will fall to the low range, and strengthening (or regeneration) can occur. Once TD 5 enters the Western Caribbean between Jamaica and Mexico's Yucatan Peninsula, a trough of low pressure passing to the storm's north may be capable of turning TD 5 more to the northwest, resulting in the storm entering the Gulf of Mexico. An equally likely scenario at this point is that TD 5 will not turn, and instead will take a more westerly path over the Yucatan Peninsula. The long-term forecast for what the storm will do once it gets to the Western Caribbean depends upon whether or not TD 5 survives during the next two days.