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98L may develop early next week

By: Dr. Jeff Masters, 2:13 PM GMT on October 10, 2012

A tropical wave located about 500 miles east of the Lesser Antilles Islands (Invest 98L) is headed west-northwest at about 15 mph, and is a threat to develop into a tropical depression early next week. The disturbance has a modest amount of spin and a large amount of disorganized heavy thunderstorms, as seen on satellite loops, but there is no sign of a surface circulation. Wind shear is a moderate 10 - 20 knots over 98L, the atmosphere is moist, and ocean temperatures are a very warm 30°C. With wind shear expected to rise to the high range, 20 - 30 knots, Wednesday night though Friday, any development the next few days should be slow. The shear is due to an upper-level trough of low pressure centered a few hundred miles northeast of the Lesser Antilles Islands. Once 98L passes beyond the Lesser Antilles on Saturday, the shearing winds of the trough will diminish to the moderate range, 10 - 20 knots. Most of the models predict that 98L will show increasing development beginning on Saturday. The NOGAPS model has 98L developing into a tropical depression on Monday, a few hundred miles northeast of the southeastern Bahama Islands. The GFS model is much slower with the system, predicting it will develop into a tropical depression on Monday, a few hundred miles north of Puerto Rico. Moisture from 98L should affect the Lesser Antilles Islands on Thursday and Friday, and Puerto Rico and the Virgin Islands on Friday and Saturday. It is uncertain if heavy rains from 98L will affect the Dominican Republic early next week; the storm may stay too far to the northeast. In their 8 am Tropical Weather Outlook, NHC gave 98L a 30% chance of becoming a tropical cyclone by Friday morning. The long range fate of 98L is uncertain; the ECMWF model shows 98L becoming absorbed by a cold front and bringing heavy rains to Canada and New England on Tuesday and Wednesday next week, while the GFS and NOGAPS models predict that 98L will stay out to sea for at least the next week.

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

Jeff Masters


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