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October 2011

Subtropical fun begins this weekend, but the trouble may not end there this month

   Posted by Levi at 8:56am on October 4, 2011

Philippe remains sheared and will likely maintain its current general intensity as it gets forced northeastward out to sea, not a threat to land.

Fun and games begin this weekend and early next week as subtropical messiness may develop in the Florida area. This is due to a stalled-out front that is currently extending down into the NW Caribbean, trapped because of strong high pressure developing over the central United States. This high pressure will be shifting eastward gradually over the eastern U.S. during the next several days, generating a strong pressure gradient that will bring brisk easterly winds into Florida. High pressure building north of a stalled front is a recipe that can often result in home-grown tropical mischief, and this setup is what we have been talking about for weeks now. Here, however, development may be subtropical at least to start out with, due to the fact that the subtropical jetstream is flowing fairly far south right now over the northern Caribbean. This means that development of low pressure will be forced to occur underneath cold air aloft on the northern side of the jet, causing the initial system to be partially cold-core, the definition of a subtropical cyclone. With SSTs still 28-29C in the Florida area, such a situation could end up fairly unstable, and a subtropical low could deepen substantially. The ECMWF and CMC models both show pressures in the 990s or lower in the eastern Gulf of Mexico 6-7 days from now.

Whether we actually get true subtropical development remains to be seen. It may just be a broad mess of rain and wind, but with or without a storm, Florida and surrounding areas will likely be in for a nasty few days of weather. Subtropical development makes sense for an initial launch of this pattern, but it will likely not end there. As the MJO progresses towards our area of the world again in one of the strongest postures that we have seen in a long time, convective activity in the southern Caribbean will likely increase, eventually being able to force the subtropical jetstream back to the north and more out of the way, allowing room for true tropical development to occur within the western Caribbean. This may take place several days after our subtropical mess is gone, but the next couple of weeks will likely see another opportunity for development, perhaps of a more truly tropical nature than what we will be dealing with early next week.

We shall see what happens!




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