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Patty little threat to the Bahamas; 98L close to tropical storm status

By: Dr. Jeff Masters, 2:50 PM GMT on October 12, 2012

Tropical Storm Patty formed late yesterday afternoon just east of the Central Bahama Islands. Patty is the sixteenth named storm of the 2012 Atlantic hurricane season, putting this year in a tie for eighth place for busiest Atlantic season since record keeping began in 1851. Patty isn't going to be around for long, though. Satellite loops show a very sickly storm, with the low-level circulation center exposed to view, and the storm's heavy thunderstorm all pushed to the northeast side of the center of circulation due to strong upper-level winds out of the southwest creating a high 20 - 30 knots of wind shear. An approaching cold front is dumping dry, stable air into Patty, and the cold front and high shear will likely destroy the storm by Saturday evening. Patty will likely have a minimal impact on the Bahamas. The storm has brought a few sporadic heavy rain showers to the Southeast Bahama Islands this morning, and this activity may continue through Saturday morning. A hurricane hunter aircraft is on its way to Patty, and will be there early this afternoon.

Figure 1. MODIS satellite image of Tropical Depression 16 taken at 11:16 am EDT Thursday, October 11, 2012. At the time, TD 16 had 35 mph winds, and was named Tropical Storm Patty six hours later. Image credit: NASA.

98L bringing heavy rain, high winds to Lesser Antilles
A strong tropical wave (Invest 98L) is bringing tropical-storm force winds and heavy rains to the Lesser Antilles this morning. At 9 am local time, winds at Barbados's Grantly Adams Airport hit a sustained 39 mph, which is minimum tropical storm-force. Wind gusts as high as 47 mph were observed on Barbados this morning. A pass from the Windsat satellite at 12:38 am EDT found that 98L had top winds of 35 mph near 17°N latitude, a few hundred miles east of Antigua. The storm is headed north-northwest to northwest at about 10 - 15 mph, and will bring tropical storm conditions to much of the Lesser Antilles Islands today and Saturday. The disturbance has plenty of spin and a large amount of moderately well-organized heavy thunderstorms, as seen on Martinique radar and satellite loops. An elongated, poorly-defined surface circulation is apparent just west of the central Lesser Antilles Islands, but satellite imagery and airport observations from the islands do not show the well-defined closed surface circulation needed for 98L to be classified as a tropical storm. An upper-level low centered a few hundred miles south of the eastern Dominican Republic is pumping dry air into the west side of 98L, and creating a high 15 - 30 knots of wind shear. An Air Force hurricane hunter aircraft is scheduled to investigate 98L this afternoon.

Figure 2. Morning satellite image of Invest 98L over the Lesser Antilles Islands.

Forecast for 98L
Wind shear is predicted to diminish to the moderate range, 15 - 20 knots, tonight through Saturday night. Given 98L's current degree of organization, the forecast drop in wind shear, and a high degree of model support for development, NHC's 8 am Tropical Weather Outlook forecast of an 80% chance of development by Sunday morning for 98L looks reasonable. I expect 98L to be upgraded later today, and it will probably skip being classified as a tropical depression and immediately be named Tropical Storm Rafael. The models are pretty well clustered for the track of 98L, taking it north-northwest through the Lesser Antilles towards Bermuda. With most of the storm's heavy thunderstorms on its east side due to dry air to the west, the Virgin Islands, Puerto Rico, and the eastern Dominican Republic are likely to see much weaker winds and less heavy rain than the Leeward Islands. The Leeward Islands can expect tropical storm conditions with occasional sustained winds of 35 - 45 mph today and Saturday as 98L moves through. The storm will make its closest pass to Bermuda on Tuesday morning, and it is possible that 98L will be capable of bringing tropical storm conditions to Bermuda. However, the track of 98L on Monday and Tuesday is rather uncertain, due to the possible interaction of the storm with the remnants of Tropical Storm Patty. 98L is not a threat to the U.S., though it could affect Newfoundland, Canada next week.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.