A new area of concern has developed near 8N 38W, about 1500 miles east of the southernmost Lesser Antilles Islands. Residents of the islands will want to keep a close watch on this tropical wave over the next few days, as it has the potential to develop into a tropical storm. The tropical wave has a concentrated area of heavy thunderstorms, some upper level outflow, and the beginnings of a surface circulation. The latest pass of the QuikSCAT satellite at 4:44am EDT today showed a strong wind shift associated with the wave, but not a closed circulation at the surface. Winds in the strongest thunderstorms were about 30-35 mph, with one heavy squall ahead of the wave creating winds of up to 50 knots (57 mph). Figure 1.
QuikSCAT winds from 4:44am EDT Fri Jul 28. The winds are plotted using the standard station model
. The black wind barbs mark where it is raining. Only the colored wind barbs are reliable. Black ones are unreliable, as rain contaminates the measurement of wind by the QuikSCAT satellite.
The wave is under about 15 knots of wind shear, and this shear is forecast to gradually weaken over the next two days, which may allow the wave to organize into a tropical depression. This organization will be slowed by the wave's close proximity to the Equator. Disturbances south of about 10 degrees north latitude frequently have trouble organizing, since they can't leverage the Earth's spin much to help them develop their own circulation. The forecast track of the system (Figure 2) takes it west at about 20 mph through Sunday, then curves it more to the west-northwest. Some very dry air laden with African dust lies to the north, so this may act to inhibit development. Once the wave nears the islands, some significant wind shear may affect it, but it is too early to be confident of this forecast. Figure 2.
Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands. Tropical wave over the Bahamas and central Caribbean
A tropical wave over the southeastern Bahama Islands extends south through the central Caribbean to Columbia. This wave is moving west-northwest at 20-25 mph, and is not expected to develop today or Saturday due to wind shear of 20 knots. The wave should reach the Gulf of Mexico on Sunday, where wind shear will be marginal for development.