949  
FXCA20 KWBC 151128  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
628 AM EST FRI DEC 15 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 15/06  
UTC: GOOD CONTINUITY WITH PREVIOUS FORECAST...WITH DIGGING TROUGH  
TO THE WEST SUSTAINING THE GRADUAL INTENSIFICATION OF A DEEP LAYER  
RIDGE ACROSS THE CARIBBEAN BASIN TO THE WESTERN ATLANTIC. AT 500  
HPA THE RIDGE IS TO ANCHOR ON A CLOSED HIGH THAT MEANDERS BETWEEN  
THE SOUTHEAST BAHAMAS/TURKS AND EASTERN CUBA. THE BUILDING RIDGE  
IS STRENGTHENING THE TRADE WINDS CAP ACROSS THE EASTERN CARIBBEAN  
ISLANDS...SUSTAINING THE EROSION OF AVAILABLE MOISTURE AND A PWAT  
MINIMA ACROSS THE FORECAST AREA. MODELS GENERALLY AGREE ON THIS  
PATTERN HOLDING THROUGHOUT NEXT WEEK.  
 
AT LOW LEVELS...A RIDGE IS FORECAST TO BUILD ACROSS THE WESTERN  
ATLANTIC/NORTH OF THE ISLANDS. UNDER INFLUENCE OF THE LOW LEVEL  
RIDGE THE WINDS ARE TO BACK TO THE EAST-NORTHEAST EARLY IN THE  
CYCLE...A PATTERN THAT IS TO PERSIST DURING THE NEXT FEW DAYS. AS  
THE GRADIENT TIGHTENS THE WINDS ARE EXPECTED TO PEAK AT 25-35KT  
DURING THE WEEKEND. THIS WILL FAVOR A COOL ADVECTIVE PATTERN  
ACROSS THE FORECAST AREA...WHILE ALSO TRIGGERING SHALLOW  
CONVECTION AS THE COOLER AIR MASS ADVECTS OVER THE WARMER WATERS  
OF THE WESTERN NORTH ATLANTIC. THE GLOBAL MODELS ALSO AGREE ON THE  
OCCASIONAL PLUMES OF MOISTURE TO ADVECT ACROSS THE FORECAST AREA  
FROM TIME-TO-TIME. THEY...HOWEVER...DISAGREE ON THE TIMING OF  
THESE PLUMES OF MOISTURE. A BLEND OF THE GFS-ECMWF WAS USED TO  
ESTIMATE THE ARRIVAL OF THESE PATCHES OF CLOUDS.  
 
THE PERSISTENT MID LEVEL RIDGE WILL INHIBIT ORGANIZED DEEP  
CONVECTION. BUT UNDER THE INFLUENCE OF THE LOW LEVEL RIDGE...AND  
POSSIBLE SHEAR LINE DURING THE WEEKEND...EXPECTING SCATTERED  
SHOWERS TO STREAM ACROSS THE FORECAST AREA DURING THE NEXT FEW  
DAYS. MOST ACTIVE IS EXPECTED BETWEEN SATURDAY AND MONDAY AS THE  
TRADE WINDS SURGE ACROSS THE FORECAST AREA. THE STRONGER WINDS ARE  
TO ALSO FAVOR GENERATION OF STREAMERS ACROSS THE VIRGIN ISLES...TO  
CLUSTER BETWEEN VIEQUES AND SOUTHEAST PUERTO RICO IN THE AFTERNOON  
HOURS. THE EAST-NORTHEAST TRADES WILL COMBINE WITH DIURNAL HEATING  
TO ENHANCE AFTERNOON CONVERGENCE ACROSS WESTERN/SOUTHWESTERN  
PUERTO RICO...WHERE WE EXPECT LIGHT TO MODERATE RAINFALL AMOUNTS  
IN A DIURNAL PATTERN.  
 
GALVEZ/DAVISON...WPC (USA)  
 

 
 
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