Watching the same two tropical waves

A tropical wave about 600 miles east of the Lesser Antilles Islands continues to be a threat as it moves west-northwest at 15-20 mph. A good pass by the QuikSCAT satellite this morning at 5:38 EDT revealed that a center of low pressure was located near 10N 51W, but the wave did not have a closed surface circulation. The main thunderstorm activity was to the north of the low's center, with winds in the 30-35 mph range at the surface. Visible satellite imagery from this morning confirm that the wave has no surface circulation, and shows a few heavy thunderstorms to the north of the center. The wave is surrounded by a large area of dry, dust-laden air to its north and west. This dry air, plus wind shear of 10-20 knots, should make any development slow to occur. However, for the first time, we do have a model that develops the wave. Last night's run of the GFDL model has the wave developing into a tropical storm by Monday night, when it crosses through the Leeward Islands near Guadeloupe. The GFDL then brings the tropical storm across the Dominican Republic on Wednesday night. None of the other models buy this solution, and predict that wind shear and dry air will keep this wave from developing. That is my expectation as well. Even if the wave does develop, a strong upper-level cold low north of the Bahamas will bring very hostile wind shear to any storm that tries to approach the U.S. East Coast. The GFDL model reflects this, and has the storm weakening as it crosses into the Bahama Islands late in the week.


Figure 1. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

Tropical wave near Puerto Rico
An area of heavy thunderstorms associated with a tropical wave lies near Puerto Rico, and has brought up to three inches of rain to eastern Puerto Rico in the past day. Long range radar out of Puerto Rico reveals no organization to the radar echoes. There is no dry Saharan air nearby, and wind shear over this disturbance is marginal for development, 15-20 knots, so some slow development is possible over the next day or two. However, the wave is headed west-northwest at about 10-15 mph into a area of higher wind shear associated with the upper-level low pressure system spinning north of the Bahama Islands. I don't expect the wave will develop, although it may bring heavy rains to Florida by Wednesday.

Monday I'll post part one of a two part series analyzing the August hurricane outlook.

Jeff Masters