Recent past, present, and near future of Western Hemisphere tropical weather

August 10, 2007

To briefly summarize tropical weather events in the western hemisphere since my last post:

Tropical Depression Three did become Tropical Storm Chantal but remained that for only twelve hours before becoming extra-tropical.

The disturbance east of the Lesser Antilles was at a relative peak when I wrote about the possibility of becoming the next tropical depression. After that, it had difficulty maintaining thunderstorm activity, which caused the low level circulation to open up. It then accelerated across the Caribbean and did become more impressive looking as time it did so. However, owing to its rapid movement it was unable to close off a circulation before going ashore. The description of it in Sunday morning’s Pacific Tropical Weather discussion was mildly amusing:

TROPICAL WAVE ALONG 88W N OF 5N AND IS MOVING W 10 TO 15 KT.
THIS WAS ABOUT AS STRONG AS A WAVE GETS BEFORE DEVELOPING INTO A
DEPRESSION. THE ONLY PROBLEM WAS IT MOVED OVER LAND..THUS
CONVECTION HAS BECOME SCATTERED. STRONGEST CONVECTION THIS
MORNING IS ON THE PACIFIC COASTS OF EL SALVADOR AND GUATEMALA
WITH ANOTHER BATCH OVER NRN GUATEMALA.

After that, the only feature of remote interest in the hemisphere was an area of low pressure that was moving westward across the Pacific.  After plodding along for a few days with multiple competing circulations, one circulation became dominant on Wednesday, which led to the rapid development of Tropical Storm Flossie.  This morning the storm intensified some more to become Hurricane Flossie, which is only the second hurricane to form in the Eastern Pacific basin this season.

Hurricane Flossie

  Eastern Pacific Hurricane Flossie

There have been conflicting forecasts from the models on the future of Flossie relative to how it may effect the Hawaiian islands.  The current NHC forecast for Flossie takes it south of the islands as a moderate tropical storm.  Because of the potential threat, a hurricane hunter will fly to check it out on Monday.

While this was going on in the Pacific, tranquility ruled nearly all of the Atlantic basin, which is in it’s longest stretch without a hurricane since the time between the last hurricane of 2000 (October 20) and the first hurricane of 2001 (September 8).  It’s been 302 days since Hurricane Isaac weakened to a tropical storm on October 2 of last year.

A big reason for the recent quiet in the Atlantic has been due to most of it being covered by dry stable air. From the visual satellite image below, one can see the western boundary of it, which runs from the southeast Bahamas southeast across the Lesser Antilles down to the Intertropcial Convergence zone.  This area extends eastward along 10 N almost all the way back to Africa.

While most of the tropical Atlantic Ocean is dominated by the dry air, the Caribbean is moist.  A few of the global forecast models have been forecasting something to form out of the western Caribbean and enter the southwest Gulf of Mexico by Tuesday of next week.  It is a plausible scenario and the western Caribbean will undoubtedly be watched closely by the National Hurricane Center for any signs of the forecast becoming reality.  One of the concerns about this scenario owes to a side-effect of the high pressure that has dominated the southeast and made it so #$%! hot: It’s resulted in a relatively cloudless Gulf of Mexico, which in turn raises Sea Surface Temperatures and increases the heat content that can serve as fuel for storms.  There is a noticable difference in the Gulf of Mexico heat potential today compared to that of a week ago.

 

Caribbean visual satellite

 

The other area that models have been forecasting development to occur in is at the opposite end of the Atlantic:

 

At the extreme right hand side of an image from this morning, one can see an area of thunderstorms that is coming off the coast of Africa.  Over the past few days, an increasing number of models have forecast development out of this as soon as Saturday evening.  The NHC will watch this closely to see if the thunderstorm activity is maintained as the system goes entirely ‘feet wet’; if it does it could be tagged as a system of interest by tomorrow morning.

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