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Western Caribbean disturbance slowly organizing

By: Dr. Jeff Masters, 4:06 PM GMT on October 07, 2007

Thunderstorm activity has increased over the Western Caribbean a few hundred miles north of the northeast coast of Honduras. This area has been labeled "Invest 94L" by NHC. This morning's QuikSCAT pass showed a sharp wind shift in the region, but not a closed circulation. Satellite loops show a steady increase in heavy thunderstorm activity, but the cloud pattern has no organization yet. Surface pressures over the entire Western Caribbean, from Cancun to Cuba, to the Cayman Islands, and south and west to Honduras and Belize have shown a large drop over the past two days. It is uncommon for pressures to fall over this large of an area during hurricane season. Wind shear is about 10 knots, and is expected to remain 10 knots or below through Tuesday. The low surface pressures, light wind shear, and warm ocean waters should allow a tropical depression to form by Tuesday at the latest. The Hurricane Hunters are scheduled to investigate the system Monday afternoon.

Steering currents are weak in the Western Caribbean, and any storm that does form may remain for a week over the high-heat content waters of the region. In that case, we can expect a hurricane a week from now. However, some of the models indicate a slow motion northwestward later this week, bringing the system over Belize or Mexico's Yucatan, before it would have a chance to intensify into a hurricane. The GFDL model predicts 94L will hit near Cozumel later this week as a tropical storm, then be forced south-westward deep into the southwestern Gulf of Mexico. There is a trough of low pressure swinging across the U.S. later this week that may be strong enough to pull 94L northwards. Western Cuba, the west coast of Florida, the Florida Keys, and the Bahamas would be at risk in this scenario. The HWRF model is the only model showing this scenario.

In the shorter term, residents of northern Honduras can expect heavy rains beginning Monday. These heavy rains will likely spread to Belize on Tuesday and Mexico's Yucatan coast by Wednesday.

Figure 1. Pressure trace at the buoy in the Western Caribbean at 20N 85W, 120 miles east of Cozumel. A steady pressure fall the past 2-3 days is apparent. Superimposed on this falling trend is an oscillation due to the pressure wave that affects all tropical stations when the rising sun makes the air expand at sunrise. Image credit: National Data Buoy Center.

Elsewhere in the tropics
A tropical wave (91L) about 500 miles east of the Lesser Antilles Islands has grown disorganized. Satellite loops show that strong upper level winds from the northwest have removed all the heavy thunderstorm activity from the center of circulation. Wind shear is expected to remain too high to allow 91L to develop. The storm is headed northwest, and is expected to recurve out to sea without affecting any land areas. A tropical disturbance a few hundred miles north of Puerto Rico (93L) has become disorganized, and is no longer a threat to develop. The system is heading slowly northwest.

Typhoon Krosa smashes into Taiwan
Typhoon Krosa made landfall on the northern tip of Taiwan yesterday as a Category 3 storm with 115 mph winds, according to Taiwan's Central Weather Bureau (CBW). Krosa, which is the Cambodian word for a species of crane, killed five people on Taiwan, and knocked out power to 700,000. The storm was apparently deflected by high terrain of the island, and rolled in a semi-circle path along the northern shore of Taiwan before heading northwest to a landfall in Mainland China as a tropical storm. Over 1 million people were evacuated in China in advance of the storm.

I'll have an update Monday morning.

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.