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August 2012

95L Trying to Develop in Western Gulf; 94L a Threat to Caribbean Islands and U.S.

   Posted by Levi at 5:39pm on August 20, 2012

Invest 95L, a spin-off from Tropical Storm Helene, is back over the water in the western Gulf of Mexico where we expected it to be today, and is starting to rotate and generate thunderstorms as the tail-end of the front driving into the northern gulf helps promote low-level convergence in the area. As we’ve been warning since Ernesto made landfall, these remnants are a threat for development off of the west gulf coast, and they have probably about 48 hours before they are forced inland over northern Mexico or extreme southern Texas by high pressure building to the north of the front. A recon plane is going to be investigating the system shortly. 95L should be mostly a rain-maker, but small, quick spin-ups like this in the gulf can surprise you, and with Humberto still haunting the recent past, these kinds of things have to be watched closely.

Invest 94L will likely be the bigger threat as it moves into the eastern Caribbean islands and potentially other land masses during the next week or so. 94L has a well-defined circulation on satellite imagery this morning, but is still lacking convection. We have seen many times big swirls like this move across the central Atlantic and struggle with the dry air there, waiting until sea surface temperature increase sharply west of 50W to finally generate thunderstorms. 94L will be approaching 50W today, and tonight and tomorrow I expect it will start to develop, and should be a tropical storm by the time it reaches the lesser Antilles. Land interaction with the greater Antilles will then modulate the intensity, but 94L will likely not have a chance to become a hurricane until it clears the Caribbean island chain.

The forecast philosophy has not changed today. A deep-layer ridge to the north of 94L should steer the system on the same W to WNW track that it has been on, bringing it into the northern Antilles in 48-60 hours. Thereafter, the upper-level pattern over eastern North America favors a weakness developing in the ridge off of the southeast United States in response to strong upper blocking over Canada and an exiting mid-latitude trough entering the NW Atlantic and eroding the subtropical ridge west of Bermuda in 48-72 hours. This should result in 94L making a gradual turn towards the northwest, crossing the Caribbean island chain and ending up near the Bahamas in about 5 days. Due to 94L developing slightly slower than expected, the forecast track has been shifted southwestward slightly after 48 hours, and now takes 94L over Hispaniola. This part of the forecast is important, because a pass over Hispaniola would be a wildcard that determines how strong 94L becomes north of the Caribbean, and could cause a jerky shift in its track. Beyond this point, uncertainty increases markedly due to an unknown amount of land interaction, and although the odds of a U.S. landfall are increasing, such a potential landfall would be 7+ days away, too far away to get specific about that part of the forecast.

We shall see what happens!

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