98L may develop this weekend; 97L no threat

A tropical wave located about 350 miles east of the Lesser Antilles Islands (Invest 98L) is headed west-northwest at about 10 - 15 mph, and is a threat to develop into a tropical depression this weekend. The disturbance has a modest amount of spin and a large amount of heavy thunderstorms, as seen on satellite loops and Barbados radar. The thunderstorms have shown more organization this morning, but there is no obvious surface circulation visible on satellite imagery. This morning's ASCAT pass showed top winds of 30 - 35 mph near 15°N, 55°W. Wind shear is a high 20 - 30 knots over 98L, the atmosphere is moist, and ocean temperatures are a very warm 30°C. With wind shear expected to diminish on Saturday to the moderate range, 10 - 20 knots, 98L may be able to develop into a tropical cyclone this weekend. The disturbance has a high amount of support for development among the reliable computer models. The NOGAPS model predicts 98L will develop into a tropical depression or tropical storm on Sunday, about 400 hundred miles north of Puerto Rico. The GFS model predicts 98L will develop on Saturday, when the center will be very close to the northernmost Lesser Antilles Islands. The ECMWF model predicts a more westerly path for 98L into the southeast Bahama Islands, with development delayed until Monday. The models are unified in forecasting that 98L will turn to the north by Monday and be drawn into a trough of low pressure. It does not appear that 98L will be a threat to the U.S. In their 8 am Tropical Weather Outlook, NHC gave 98L a 50% chance of becoming a tropical cyclone by Saturday morning. A hurricane hunter aircraft is scheduled to visit 98L on Friday afternoon.


Figure 1. Morning satellite image of Invest 98L approaching the Lesser Antilles Islands.

Invest 97L east of the Bahamas
A tropical wave located about 250 miles east of the central Bahama Islands (Invest 97L) is headed slowly southwards. The disturbance is well-organized, with a developing surface circulation and a respectable area of heavy thunderstorms, as seen on satellite loops. Wind shear is a high 20 knots over 97L, and the shear has pushed all the storm's heavy thunderstorms to its east side. Shear is expected to increase sharply later today as a cold front overtakes the system. This cold front should be capable of destroying 97L by Friday.

Jeff Masters