691  
FXCA20 KWBC 081245  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
745 AM EST FRI DEC 08 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 08/06  
UTC: UNDER THE INFLUENCE OF A LARGE TROUGH DEEPENING IN THE  
WESTERN UNITED STATES...A HIGH AMPLITUDE UPPER RIDGE IS BUILDING  
OVER THE CARIBBEAN. THE RIDGE LIES WELL TO THE WEST OF AN UPPER  
TROUGH...THAT CENTERS ON A LOW AT 31N 38W...WHICH IS SUSTAINING A  
WEAKENING SURFACE FRONT THAT HAS ALREADY MEANDERED TO THE SOUTH OF  
THE ISLANDS. THE ILL-DEFINED FRONT NOW EXTENDS ACROSS  
DOMINICA...WEST ALONG 16N/17N...INTO SOUTHERN HISPANIOLA. AT 500  
HPA...A RIDGE CENTERS ON A HIGH AT 22N 64W...AND HAS NOW BUILT TO  
EXTEND OVER THE SOUTHEASTERN BAHAMAS...HISPANIOLA...PUERTO  
RICO...AND THE NORTHEASTERN ANTILLES. THIS RIDGE...IN COMBINATION  
WITH THE DRIER AIR MASS TO THE NORTHEAST OF THE SURFACE  
FRONT...WILL FAVOR MOSTLY FAIR CONDITIONS IN THE ISLANDS. ALTHOUGH  
SLIGHT COLD ADVECTION WILL CONTINUE DURING FRIDAY...WHICH USUALLY  
FAVORS LIGHT TRADE WIND SHOWERS DUE TO A DECREASE OF STABILITY  
CLOSE TO THE OCEAN SURFACE...THE AIR MASS ARRIVING FROM THE EAST  
IS QUITE DRY AND ENHANCEMENT OF SHOWERS WILL BE LIMITED.  
 
DURING FRIDAY AND SATURDAY...TRADE WINDS ARE TO REMAIN STRONG WITH  
SPEEDS OF 15-20KT. THE BASE OF THE TRADE WIND INVERSION WILL  
OSCILLATE BETWEEN 900 AND 850 HPA. THIS WILL LEAD TO LIGHT AND  
ISOLATED SHOWERS...WHICH WILL PEAK IN COVERAGE AND INTENSITY IN  
LATE NIGHT/EARLY MORNING HOURS ACROSS EASTERN PUERTO RICO.  
EXPECTING ISOLATED ACCUMULATIONS UNDER 0.2 IN/DAY. TRADE WINDS  
WILL DECREASE IN SPEED DURING SATURDAY EVENING...WHEN A WEAK  
PERTURBATION IN THE TRADES WILL ARRIVE FROM THE EAST. THIS WILL  
LEAD TO A MINOR ENHANCEMENT IN SHOWERS ON LATE SATURDAY INTO  
SUNDAY...MOSTLY ACROSS THE VIRGIN ISLANDS AND EASTERN PUERTO RICO.  
ACCUMULATIONS WITH THE SCATTERED SHOWERS WILL PRODUCE SCATTERED  
TOTALS OF 0.2-0.3 INCHES/DAY THROUGH MIDDAY SUNDAY.  
 
AFTER MIDDAY SUNDAY...TRADE WIND SHOWERS ARE TO DECREASE ONCE  
AGAIN IN COVERAGE AND INTENSITY. TRADE WINDS WILL CONTINUE  
WEAK...WITH SPEEDS OF 05-10KT...AND FROM THE EAST-NORTHEAST. THIS  
WILL FAVOR LIGHT AND ISOLATED RAIN SHOWERS IN EASTERN AND  
NORTHEASTERN PUERTO RICO DURING EARLY MORNING HOURS...GIVING WAY  
TO LIGHT RAIN SHOWERS IN THE SOUTHWESTERN CORDILLERA IN THE  
AFTERNOON. DAILY RAINFALL ACCUMULATIONS FROM SUNDAY MIDDAY INTO  
TUESDAY WILL BE UNDER 0.15 INCHES/DAY.  
 
NO SIGNIFICANT WET SPELL IS ON SITE SO FAR...AS THE STRONG FRONTAL  
SYSTEM DEVELOPING IN THE GULF OF MEXICO/UNITED STATES IS FORECAST  
TO STALL IN HISPANIOLA DURING EARLY NEXT WEEK.  
 
GORDON...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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