375  
FXCA20 KWBC 191132  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
632 AM EST SUN NOV 19 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 19/06  
UTC: AT 500 HPA...NARROW/ELONGATED TROUGH STRETCHES FROM THE  
EASTERN ATLANTIC ALONG 23N/24N TO THE SOUTHEAST BAHAMAS...WHERE IT  
THEN CONTINUES ACROSS THE WINDWARD PASSAGE TO CENTRAL AMERICA.  
BUILDING CELL OF THE SUBEQUATORIAL RIDGE LIES TO THE EAST...SLOWLY  
ENTRENCHING ACROSS THE EASTERN CARIBBEAN. THIS RIDGE...IN  
INTERACTION WITH THE TROUGH TO THE WEST...FAVORS A MID/UPPER LEVEL  
SOUTHWESTERLY FLOW ACROSS THE NORTHEAST CARIBBEAN ISLES. AN AREA  
OF ORGANIZED CONVECTION OVER THE CENTRAL CARIBBEAN ASSOCIATES WITH  
MEANDERING LOW LEVEL CYCLONE SOUTH OF HISPANIOLA. THE  
SOUTHWESTERLY FLOW ALOFT IS DRAWING A PLUME OF DEEP TROPICAL  
MOISTURE ACROSS THE NORTHEAST CARIBBEAN ISLES...FAVORING PWAT  
CONTENT OF TWO INCHES AS MOISTURE POOLS ACROSS THE FORECAST AREA.  
 
CONSISTENT WITH PREVIOUS FORECAST... EXPECTING MID LEVEL TROUGH  
AXIS TO SLOWLY WEAKEN OVER THE NEXT DAY OR SO AS A HIGH AMPLITUDE  
TROUGH DEEPENS ACROSS THE USA-GULF OF MEXICO-SOUTHERN MEXICO. IN  
RESPONSE TO THE DEEPENING TROUGH TO THE WEST...THE CELL OF THE  
SUBEQUATORIAL RIDGE TO THE EAST IS TO RAPIDLY BUILD ACROSS THE  
ISLAND CHAIN TO THE EASTERN CARIBBEAN. THIS IS FORECAST TO  
STRENGTHEN THE TRADE WINDS CAP ON MONDAY-TUESDAY...WHEN IT IS  
EXPECTED TO SETTLE AROUND 800/850 HPA. THIS WILL BE ACCOMPANIED BY  
GRADUAL EROSION OF AVAILABLE MOISTURE...WITH PWAT MINIMA OF  
1.25-1.50 INCHES EXPECTED LATER ON TUESDAY. AT LOW LEVELS...WANING  
CYCLONIC CIRCULATION SOUTH OF HISPANIOLA IS TO INITIALLY FAVOR A  
SOUTH-SOUTHEAST LOW LEVEL FLOW. THIS IS TO MEANDER WEST ACROSS THE  
CARIBBEAN...AND AS IT MOVES AWAY THE PREVAILING EASTERLY TRADES  
RETURN TO THE FORECAST AREA ON MONDAY. EARLY IN THE CYCLE THE  
SOUTH-SOUTHEAST FLOW IS TO ENHANCE MOISTURE CONVERGENCE ACROSS  
NORTHERN PORTIONS OF PUERTO RICO DURING THE DAY TODAY. THE GFS GDI  
FORECAST SHOWS BEST INSTABILITY AROUND 18-21 UTC TODAY OVER  
WESTERN PORTIONS OF PUERTO RICO. AS A RESULT...EXPECTING THE MOST  
ACTIVE CONVECTION TO CLUSTER ACROSS NORTHWEST/WESTERN INTERIOR  
PORTIONS OF PUERTO RICO...WITH MAXIMA RANGING BETWEEN 1-3 INCHES.  
ACROSS SAINT CROIX EXPECTING MODERATE RAINFALL AMOUNTS CAPPING AT  
LESS THAN AN INCH...WHILE OVER THE NORTHERN VI EXPECTING RAINFALL  
AMOUNTS TO RANGE BETWEEN A QUARTER TO HALF AN INCH. LINGERING  
SHALLOW INSTABILITY ON MONDAY IS TO ONLY FAVOR LIGHT TO MODERATE  
RAINFALL AMOUNTS...WITH MOST ACTIVE ACROSS NORTHWEST PUERTO RICO  
WHERE THE MAXIMA IS TO RANGE BETWEEN A QUARTER TO HALF AND INCH.  
 
DURING MEDIUM RANGE PERIOD...AS MID/UPPER LEVEL TRADE WINDS CAP  
REMAINS...EXPECTING MOSTLY FAIR WEATHER CONDITIONS TO PREVAIL.  
HOWEVER...IN BRISK EASTERLY TRADES...THE OCCASIONAL CLOUD CLUSTER  
IS TO STREAM ACROSS THE VIRGIN ISLES TO EASTERN PUERTO RICO FROM  
TIME-TO-TIME. BUT THESE ARE TO ONLY FAVOR LIGHT RAINFALL AMOUNTS  
IN PASSING RAIN SHOWERS.  
 
DAVISON...WPC (USA)  
 

 
 
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