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Western Caribbean disturbance 96L close to tropical depression status

By: Dr. Jeff Masters, 3:21 PM GMT on October 23, 2011

A region of disturbed weather in the Western Caribbean (Invest 96L) has become more organized this morning, and is close to tropical depression status. A hurricane hunter aircraft is scheduled to investigate 96L this afternoon at 2 pm EDT to see if a tropical depression has formed. The system is located just offshore from the Nicaragua/Honduras border, and is bringing heavy rains to northeastern Honduras. Visible satellite loops show that 96L is close to having a well-developed surface circulation, but the heavy thunderstorm activity is all on the west side of the center, due to a large region of dry air to the east. Wind shear is a moderate 10 - 20 knots due to strong upper-level winds out of the east, and these winds are injecting dry air into 96L's east side, keeping any heavy thunderstorms from developing on that side. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.

Figure 1. Morning satellite image of 96L.

Forecast for 96L
I expect 96L will be able to organize into a tropical depression later today or on Monday, though this process will be slowed by the dry air to the storm's east, and perhaps by proximity to the land areas of Nicaragua and Honduras. NHC gave 96L a 60% chance of developing into a tropical depression by Tuesday in their 8 am Tropical Weather Outlook today. Steering currents favor a motion to the west-northwest or northwest, and it is likely that heavy rains from 96L will spread over Belize by Tuesday night, when the storm will probably be called Tropical Storm Rina. Heavy rains from the storm will spread over Mexico's Yucatan Peninsula, including Cozumel and Cancun, by Wednesday afternoon. On Wednesday, 96L will be encountering a dry airmass with high wind shear that lies over the extreme northwestern Caribbean. Since 96L is a small storm, these hostile conditions should cause the storm to weaken significantly before any potential landfall occurs.

A broad region of low pressure near 11°N, 55°W, about 300 hundred miles east of the southern Lesser Antilles Islands (Invest 97L), is moving slowly west-northwest towards the Lesser Antilles. This low has very limited heavy thunderstorm activity, due to dry air. NHC is giving 97L just a 10% chance of developing into a tropical depression by Tuesday. 97L is under a moderate 10 - 20 knots of wind shear, and this shear is expected to drop to the low range, less than 10 knots, by Monday, when the storm will be in the Eastern Caribbean Sea. By the time 97L approaches Jamaica in the Central Caribbean on Friday, the storm should find a moister environment, and could develop into a tropical depression then, as predicted by the NOGAPS model.

Jeff Masters


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