609  
FXCA20 KWBC 311137  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
636 AM EST WED JAN 31 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 31/06  
UTC: POLAR TROUGH MOVING ACROSS THE WESTERN ATLANTIC IS DISPLACING  
A RIDGE SOUTH OVER THE BASIN. AS IT SETTLES OVER THE CARIBBEAN  
THIS IS STRENGTHENING THE TRADE WINDS CAP OVER THE FORECAST  
AREA...WITH INVERSION TO MEANDER BETWEEN 750/800 HPA DURING THE  
NEXT FEW DAYS. THIS...IN-TURN...FAVORS THE EROSION OF AVAILABLE  
MOISTURE FROM THE EAST...AND WILL LEAD TO MOSTLY FAIR WEATHER  
CONDITIONS DURING THE NEXT TWO DAYS. AT LOW LEVELS...POLAR RIDGE  
IS ROLLING ACROSS THE EASTERN USA...FAVORING A BRISK  
NORTH-NORTHWESTERLY FLOW ACROSS THE WESTERN ATLANTIC. THIS IS  
DRIVING A SURFACE FRONT ACROSS THE CENTRAL ATLANTIC WHILE TRAILING  
ACROSS THE BAHAMAS TO CUBA. BOUNDARY LAYER WINDS ACROSS THE  
FORECAST AREA REMAIN FROM THE EAST...WHILE AT 850 HPA THE WINDS  
BACKED TO THE NORTHEAST. THIS...HOWEVER...WILL BE SHORT  
LIVED...WITH PREVAILING EASTERLY TRADES TO RETURN LATER THIS  
AFTERNOON.  
 
MID LEVEL RIDGE IS TO THEN ANCHOR ON A MEANDERING HIGH OVER THE  
YUCATAN/NORTHWEST CARIBBEAN THROUGH THE MEDIUM RANGE PERIOD. AS  
THE RIDGE PATTERN HOLDS OVER THE NORTHERN CARIBBEAN ISLES...THE  
ASSOCIATED TRADE WINDS CAP IS EXPECTED TO PERSIST. THIS IS TO  
CONTINUE INHIBITING ORGANIZED DEEP CONVECTION DURING THE NEXT FEW  
DAYS. AT LOW LEVELS...SURFACE FRONT LOSES ITS UPPER LEVEL SUPPORT  
EARLY IN THE CYCLE...WITH BOUNDARY FORECAST TO BOTTOM OUT TO THE  
NORTH OF 23N/24N LATER THIS EVENING EARLY THURSDAY MORNING.  
FRONTAL BOUNDARY IS TO THEN FRONTOLIZE LATER ON THURSDAY/EARLY  
FRIDAY MORNING. FURTHERMORE...POLAR RIDGE ROLLING ACROSS THE  
EASTERN USA IS TO SETTLE OVER THE WESTERN ATLANTIC EARLY IN THE  
CYCLE. THE RIDGE WILL THEN SUSTAIN A TIGHT GRADIENT AND BRISK  
EAST-NORTHEAST WINDS ACROSS THE FORECAST AREA. THE BOUNDARY LAYER  
WINDS ARE EXPECTED TO PEAK AROUND 15-20KT FROM TIME-TO-TIME...A  
PATTERN THAT HOLDS THROUGH THE REST OF THE WEEK AND THE WEEKEND.  
PWAT MINIMA ACROSS THE FORECAST AREA WILL PERSIST THROUGH THURSDAY  
EVENING...WITH LIGHT CONVECTION LIMITING TO EL YUNQUE AND THE  
CORDILLERA. OTHERWISE...FAIR WEATHER CONDITIONS ARE TO PREVAIL.  
 
LATER IN THE WEEK/WEEKEND THE MODELS AGREE ON IRREGULARLY SPACED  
SHALLOW CLOUD CLUSTERS/WEAK PERTURBATIONS IN THE LOW LEVEL TRADES  
TO THEN ADVECT FROM THE EAST-NORTHEAST. BUT AS A STRONG TRADE  
WINDS CAP HOLDS...THESE ARE TO ONLY FAVOR LIGHT RAINFALL AMOUNTS  
IN PASSING SHOWERS. OTHER CONVECTION WILL ASSOCIATED WITH BRISK  
EAST-NORTHEASTERLY WINDS OVER THE VIRGIN ISLES TRIGGERING  
STREAMERS THAT ARE TO AFFECT EASTERN PORTIONS OF PUERTO RICO.  
THESE WILL LIKELY FAVOR MEASURABLE RAINFALL AMOUNTS...WITH MOST  
ACTIVE BETWEEN FAJARDO-LUQUILLO-EL YUNQUE. A SECONDARY MAXIMA IS  
EXPECTED OVER SOUTHWEST PUERTO RICO...WITH RAINFALL AMOUNTS  
PEAKING AROUND A QUARTER OF AN INCH IN AFTERNOON CONVECTION.  
 
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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