African Tropical Wave 98L a Marginal Threat to Develop

A strong and well-organized tropical wave moved off the coast of Africa on Monday, and has been designated 98L by NHC. This disturbance is headed west at 10 - 15 mph, and is under a moderate 10 - 15 knots of wind shear. A large amount of dry air lies to the north and west of 98L, and will likely interfere with development. The SHIPS model predicts that wind shear will stay in the moderate range through Thursday, then rise to the high range, 20 - 30 knots, on Friday and Saturday. Ocean temperature are warm off the coast of Africa (27 - 28°C,), but will cool to 25 - 26°C on Tuesday through Thursday, a temperature that is quite marginal for development. None of the computer models predict that 98L will develop, not even the usually aggressive Canadian (CMC) model. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 98L a 10% chance of developing into a tropical cyclone by Wednesday. 98L should maintain a west to west-northwest track through the week, and may bring heavy rains and gusty winds to the northern Lesser Antilles Islands beginning on Saturday night.


Figure 1. Satellite image of 98L off the coast of Africa taken at 8 am EDT Monday July 22, 2013, with a satellite analysis of where dry air is, as well. A large amount of dry air lies to the north and west of 98L, and will likely interfere with development. Image credit: University of Wisconsin CIMSS and NOAA/HRD.


Figure 2. MODIS satellite image of 98L taken at approximately 8 am EDT July 22, 2013. Image credit: NASA.

Jeff Masters