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May 2012

Watching for Tropical Stirrings in the Caribbean May 20th – June 5th

   Posted by Levi at 7:43pm on May 10, 2012

The time of year has come to start watching for our first tropical system to form in the Atlantic. The period from May 20th through June 5th is starting to look favorable for monsoonal activity to invade the western Caribbean and move north or northeast into the eastern Gulf of Mexico or the Bahamas. Convection should be enhanced in the area by a Madden-Julian Oscillation (MJO) pulse coming eastward into the eastern Pacific and western Caribbean in a couple of weeks. The model MJO forecasts below show the GFS being the most bullish, which is not surprising.

In fact, the GFS showed this happening 3 weeks ago. I don’t mean that it saw this event 3 weeks in advance. I mean that saw it happening way too early, and that is a model failing. Indeed, the GFS has been showing a tropical storm in the western Caribbean on almost every run for 3 weeks now in the western Caribbean, which until now has made no sense. However, it is worth mentioning now, because the pattern is more supportive for this to occur. A slower MJO progression as shown by the European models is called for, indicating that at some point during the May 20th-June 5th period we should see a pickup in tropical thunderstorm activity in the Caribbean that could lead to an early storm. This is this morning’s 12z GFS run’s depiction of the storm at Day 11, which may still be a bit too early:

Additionally, the upper pattern around this time is looking suspicious for tropical activity. The GFS ensembles have the polar jet retreating into southern Canada, with general ridging over the central and eastern United States. However, 500mb heights consistently sag south and east of the U.S., with a weak trough of some kind hanging back and reaching into the NW Caribbean, a pattern indicative of upward motion occurring in the tropics, and a trough becoming involved in the monsoonal circulation in the early season is a good way to get a quick tropical storm that gets drawn out of the Caribbean.

Now this is still nearly 2 weeks out, so details will be scarce until the time draws nearer, but if we do get some kind of a development, expect it to be drawn out of the western Caribbean northward into either the eastern Gulf of Mexico or across Cuba into Florida or the Bahamas, but likely being sheared to the east as it goes, typical of early-season systems. If anything the pattern should turn wet for these areas, hopefully bringing needed tropical rains to Florida. It is also possible that the eastern Pacific will see activity and possibly their first storm before the Atlantic has a chance to see any action. The time has come to start monitoring the tropics again.

We shall see what happens!