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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1203Z Feb 14, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
703 AM EST WED FEB 14 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 14/06
UTC: THE EASTERN CARIBBEAN IS UNDER THE INFLUENCE OF A LARGE UPPER
TROUGH THAT EXTENDS ACROSS MOST OF THE TROPICAL ATLANTIC...AND
EXTENDS AN AXIS INTO THE EASTERN CARIBBEAN ALONG 13N-16N. THE
TROUGH HAS WEAKENED THE SUBSIDENCE CAP ACROSS THE BASIN. THIS IS
LEADING TO POCKETS OF TRADE WIND SHOWERS WITH VERTICAL DEVELOPMENT
UP TO 750-600 HPA. THE MOST SIGNIFICANT FACTOR IN LIMITING
RAINFALL ACCUMULATIONS IS THE LOW MOISTURE CONTENT ABOVE 700 HPA.
GIVEN THE UNSTABLE BOUNDARY LAYER...THE DRY AIR IS BEING MIXED-IN
INTO THE MARINE LAYER LEADING TO SHORT-LIVED TOWER CUMULUS. A
SECOND FACTOR ARE THE STRONG TRADES...FROM THE EAST-NORTHEAST
PEAKING AT 925 HPA WITH SPEEDS OF 30-35KT OVER PUERTO RICO. THESE
ARE LEADING TO VERY BRIEF ACCUMULATION PERIODS.

THE UPPER TROUGH AXIS IS FORECAST TO MEANDER TO THE EXTEND ACROSS
THE EXTREME SOUTHEASTERN CARIBBEAN ON SATURDAY. AT LOW
LEVELS...THE STRONG TRADE WINDS ARE FORECAST TO DECREASE IN
INTENSITY ON WEDNESDAY FROM 30-35KT TO 15-25KT...TO INCREASE AGAIN
DURING THE WEEKEND. THE SUBSIDENCE CAP IS FORECAST TO STRENGTHEN
THROUGH THE CYCLE...TO CONTINUE LIMITING THE DEVELOPMENT OF
THUNDERSTORMS. THE VARIABILITY IN PRECIPITATION WILL BE MOSTLY
MODULATED BY OSCILLATIONS IN THE STRENGTH AND ELEVATION OF THE
TRADE WIND CAP AND ASSOCIATED MOISTURE CONTENT...IN POCKETS OF
ARRIVING TRADE WIND SHOWERS. RAINFALL ACCUMULATIONS WILL PEAK ON
WEDNESDAY FOLLOWED BY A GRADUAL DECREASE UNDER INFLUENCE OF THE
STRENGTHENING CAP.

GORDON...NMS (BELIZE)
NIXON...BDM (THE BAHAMAS)
GALVEZ...WPC (USA)