Meanwhile, in the Atlantic…

June 20, 2010

This time last week, there was a bit of excitement over an area of low pressure in the deep tropics. Even though it was in a very unusual area for tropical cyclone formation this early in the year, the National Hurricane Center was concerned about seemingly favorable conditions and at one point had raised the probability of formation up to 60%.  However, climatologically normal conditions (e.g. high shear) prevailed to keep the low from developing further.  A look at the past five days (starting from yesterday morning, at the bottom) can be seen below. By looking at the bottom frame, around Puerto Rico and working up and to the right through previous days, one can see the daily fluctuation in thunderstorms associated with this system. (In the Pacific, the formation of Tropical Storm Blas (on the 17th) can be seen as well as the genesis of what would become Hurricane Celia.)

Today, the system that caused the excitement last week is dumping rain over Hispanola and Puerto Rico and is expected to move westward without further incident.  However, the tropical wave to its east may be of interest.

This evening’s Tropical Weather Outlook points out the tropical wave just west of the Lesser Antilles and notes that while it will produce heavy rains and gusty winds across the islands and northern Venezuela during the next day, “upper level winds are marginally conducive for tropical cyclone development” and gives the system a low chance-10% of developing during the next 48 hours.

However, for multiple reasons, the potential interest in this system lies in the future as it moves further west in the Caribbean.  For over a week, the Tropical Cyclone Formation Probability Product has been pointing out the northwestern Caribbean/southwest Gulf of Mexico as an area where TC formation is possible due to past climatology and current favorable conditions. For example, for most of this month wind shear in the Gulf of Mexico has been at a quite favorable level, well below the climatological norm.  However, there haven’t been any catalysts, in the form of tropical waves or other disturbed weather, to trigger TC formation.

A few global forecast models run his morning are suggesting that the wave currently in the southeast Carribean may be a catalyst.  NOGAPS and the ECMWF models show a similar situation six days out, with a system forming northwest of Jamaica six days out, headed to the Gulf of Mexico.  The Canadian shows a different scenario involving TC formation in the west Caribbean at the end of the forecast period.

Given the extended time period (beyond 3 days) that the models show development, the forecast is speculative, at best. Indeed, if it were only one of these models showing development, I wouldn’t consider it worth mention (the Canadian is notorious for generating “boguscanes”, while the fairly reliable NOGAPS has had an odd tendency to develop lows out of the southwest Caribbean towards the end of a forecast period every few runs).   However, these models together, along with the climatological favor for development in the area forecast, make me think there may be something to it. (The burst of activity in the eastern Pacific over the past week, which sometimes seems to indicate an oscillation of favorable atmospheric conditions that shifts to the Atlantic, where tropical cyclone formation subsequently occurs is a small point in favor of the scenario as well.)

Something to watch as the week progresses.

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