| Invest 90L: an African wave worth watching An African wave (Invest 90L) near 14N 55W, 400 miles east of the Lesser Antilles Islands, is moving west-northwest at about 15 - 20 mph. This wave is generating a limited amount of heavy thunderstorms due to the presence of a large amount of dust and dry air from the Sahara, and will spread heavy rain showers and strong gusty winds to the northern Lesser Antilles tonight through Saturday. The wave has a modest degree of spin to it, and is under low wind shear, 5 - 10 knots. Dry air will continue to be a problem for 90L through Sunday, but once it finds a moister environment near the Bahama Islands early next week, it could develop. However, the expected track of the disturbance takes it over the rugged terrain of Hispaniola, which would inhibit development. Furthermore, wind shear is expected to rise to the moderate range, 10 - 20 knots, on Saturday, and could increase further by Monday, according to most of the computer models. Of the latest 00Z and 06Z runs of the four reliable models for predicting formation of a tropical depression, only the NOGAPS model shows development of 90L. The NOGAPS predicts the wave could attain tropical depression status on Tuesday, over the northwestern Bahama Islands just off the coast of Southeast Florida. The other models generally depict too much wind shear for the wave to develop. Right now, the deck appears stacked against development for 90L through at least Monday. NHC is predicting a 20% chance of development by Sunday. The eventual track of 90L next week has been trending more to the south in recent model runs, as they are generally depicting a weaker trough of low pressure developing over the Eastern U.S. This reduces the chances 90L will move up the U.S. East Coast, and increases the chances that it will enter the Gulf of Mexico. |