608  
FXCA20 KWBC 161150  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
749 AM EDT MON OCT 16 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE VI FROM OCT 15/06  
UTC: A TROPICAL WAVE HAS CROSSED THE ISLANDS AND CENTERS AT 70W.  
MOST OF THE DEEP CONVECTION WITH THIS WAVE IS WELL TO THE NORTH OF  
THE ISLANDS AS IT IS INTERACTING WITH AN UPPER TROUGH LOCATED OVER  
THE NORTHERN BAHAMAS. THIS UPPER TROUGH LIES TO THE SOUTHEAST OF A  
LARGE POLAR TROUGH THAT EXTENDS ALONG THE EASTERN COAST OF THE  
UNITED STATES. THE INTERACTION BETWEEN THESE TROUGHS WILL HAVE AN  
IMPACT IN THE PRECIPITATION IN PUERTO RICO AND THE VI. AT  
LOW-LEVELS...A MOISTURE PLUME ASSOCIATED WITH THE ITCZ EXTENDS  
INTO THE FRENCH ANTILLES. A TRADE WIND SURGE TRAILS BEHIND WHILE  
EXTENDING NEAR 50W. IN THE ISLANDS...TRADES HAVE SPED UP AND ARE  
FROM THE EAST-SOUTHEAST AT 15-25KT.  
 
MODELS AGREE IN CONVECTIVE INSTABILITY REMAINING HIGH THROUGH  
WEDNESDAY...AND SHARPLY DECREASING AFTER...AS THE TRADE WIND SURGE  
ARRIVES. THE TRADE WIND SURGE WILL ARRIVE ON WEDNESDAY EVENING  
ACCOMPANIED BY A STRONG SUBSIDENCE CAP THAT IS FORECAST TO SIT  
NEAR 900 HPA. THIS WILL LEAD TO A SIGNIFICANT DECREASE IN  
PRECIPITATION FROM LATE WEDNESDAY AND ON. THE TRADE WIND SURGE  
WILL ALSO ARRIVE ACCOMPANIED BY WINDS OF 20-30KT. THIS WILL LEAD  
TO STRONG LOW-LEVEL SHEAR AND FAST MOVING ISOLATED TRADE WIND  
SHOWERS...WHICH ARE TO PRODUCE TRACE ACCUMULATIONS.  
 
IN THE MEAN TIME...TRADES ARE TO REMAIN AT 15-25KT FROM THE  
SOUTHEAST THROUGH THE CYCLE...COMBINED WITH A CONVECTIVELY  
UNSTABLE AIR MASS. THE AMOUNT OF LOW-LEVEL SHEAR WILL LIMIT THE  
DEVELOPMENT OF HEAVY RAIN-PRODUCING THUNDERSTORMS. LARGEST  
ACCUMULATIONS WILL BE MORE ASSOCIATED WITH OROGRAPHIC UPLIFT AS  
THE FLOW AND TRADE WIND SHOWERS/THUNDERSTORMS INTERACT WITH  
MOUNTAIN RANGES IN PUERTO RICO. THIS WILL FAVOR LARGEST  
ACCUMULATIONS IN EASTERN AND SOUTHEASTERN PUERTO RICO. THROUGH  
WEDNESDAY...EXPECTING MAXIMA OF 1.5-2.5 INCHES IN EASTERN PUERTO  
RICO...AND MAXIMA NEAR 1 INCH ALONG SOUTHEASTERN PUERTO RICO.  
ISOLATED AFTERNOON THUNDERSTORMS ARE TO PRODUCE ISOLATED MAXIMA OF  
0.75 INCHES IN EXTREME NORTHWESTERN PUERTO RICO. IN THE VIRGIN  
ISLANDS...EXPECTING AN INCREASE IN NOCTURNAL CONVECTION ON TUESDAY  
EVENING-EARLY WEDNESDAY...WHERE EXPECTING MAXIMA NEAR 1 INCH.  
OTHERWISE...ACTIVITY WILL OCCUR IN THE FORM OF FAST PASSING LIGHT  
TRADE WIND SHOWERS.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
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