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October 2011

(Sub)Tropical troubles begin this weekend near Cuba, Bahamas, and Florida

   Posted by Levi at 11:22am on October 3, 2011

Ophelia is now brushing Newfoundland with tropical storm conditions and is headed into extratropical transition. Tropical Storm Philippe, as explained last week, is destined to recurve out to sea due to a front sitting over Bermuda, and is no threat to land.

The models are really starting to latch onto the potential for tropical mischief in the Caribbean, eastern gulf, and Bahamas area starting sooner than they thought a few days ago. I mentioned over the weekend that starting October 7th we needed to watch things, and now the models are showing the potential for trouble as soon as this weekend, just as the pattern has dictated. The models are actually trying to show subtropical development east of Florida, which is north of the Caribbean instead of inside of it. This could make sense as a first-stage event, given that the MJO will not be fully into the Caribbean yet in 6-8 days, so the subtropical jetstream will still be riding pretty far south, allowing development in the cold pool aloft to its north. Development would be stimulated by a big surface high over the eastern United States, bringing a strong pressure gradient and up to gale-force winds into Florida for several days, with or without subtropical development. Nasty weather is in store for that state.

A subtropical development would have a chance to move northeastward out to sea, but it could also get trapped beneath the eastern U.S. ridge if the ridge is pushed far enough eastward by the Pacific jetstream. This could make sense due to the MJO’s aggressive move across the Pacific that is now beginning. The CMC takes this scenario to the house and shows a 988mb low retrograding westward across Florida by Day 10 with a 500-mile-wide area of gale-force winds, a very nasty situation.

Whether we actually get subtropical development can’t be guaranteed yet. We need to get closer in on the situation before we can be sure what will happen initially south of the big high. However, even without development this weekend, this pattern could spark multiple instances of mischief in different places. While a subtropical feature may be the way to start off this pattern, once the MJO becomes entrenched in the Caribbean, it will likely push the subtropical jetstream northward and allow an opportunity for a deep tropical system to develop within the western Caribbean, more attuned to the historical ideas I have presented over the last few weeks. This pattern is such that we could get two named systems out of a 10-15 day period of fun and games from the Caribbean up through the Bahamas and Florida area starting this weekend.

We shall see what happens!



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