319  
FXCA20 KWBC 071134  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
634 AM EST TUE NOV 07 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 07/12  
UTC: MID/UPPER LEVEL TROUGH EXTENDS TO THE SOUTH-SOUTHWEST ACROSS  
THE SOUTHEAST BAHAMAS-EASTERN CUBA/JAMAICA TO THE CENTRAL  
CARIBBEAN. A CELL OF THE SUBEQUATORIAL RIDGE TO THE EAST EXTENDS  
OVER THE EASTERN CARIBBEAN. AS THE TROUGH PRESSES AGAINST THE  
RIDGE TO THE EAST...TIGHTENING THE UPPER GRADIENT...THIS FAVORS AN  
UPPER DIVERGENT PATTERN THAT IS VENTING DEEP CONVECTION ACROSS THE  
NORTHEAST CARIBBEAN ISLES. AT LOW LEVELS...THE TROUGH ALOFT IS  
INDUCING THE NORTHWARD AMPLIFICATION OF AN INVERTED TROUGH ACROSS  
THE CENTRAL CARIBBEAN. THIS...IN-TURN...SUSTAINS A MOIST  
SOUTHEASTERLY FLOW ACROSS THE EASTERN CARIBBEAN...POOLING OVER THE  
FORECAST AREA WHERE IT SUSTAINS PWAT CONTENT OF TWO INCHES.  
 
UPPER LEVEL TROUGH IS TO GRADUALLY WEAKEN LATER ON THURSDAY AS A  
HIGHER AMPLITUDE TROUGH DEEPENS ACROSS THE GULF. AT 500 HPA THIS  
IS TO EVOLVE INTO TWO PERTURBATIONS...WITH A CLOSED LOW OVER THE  
CENTRAL CARIBBEAN AND A WEAKER LOW NEAR THE TURKS/SOUTHEAST  
BAHAMAS. UNDER INFLUENCE OF THE MID LEVEL CYCLONE...AN 850 HPA LOW  
IS TO CLOSE OVER THE CENTRAL CARIBBEAN. THIS WILL HELP SUSTAIN THE  
MOIST SOUTHEASTERLY FLOW THROUGH THE END OF THE WEEK...WITH PWAT  
CONTENT OF TWO INCHES FORECASTS TO PERSIST THROUGH EARLY NEXT  
WEEK. ALTHOUGH MOISTURE CONTENT IS HIGH...BEST DYNAMICAL SUPPORT  
IS TAKING PLACE NORTH OF THE FORECAST AREA. BUT AS ACTIVITY TO THE  
NORTH WAXES AND WANES...THERE WILL BE PERIODS OF MODERATE TO HEAVY  
CONVECTION ACROSS PUERTO RICO AND THE US VIRGIN ISLES. MOST ACTIVE  
FOR THE ISLANDS IS EXPECTED IN THE AFTERNOON HOURS...WHILE THE  
CONVECTION TO THE NORTH IT IS EXPECTED TO PEAK DURING THE MORNING  
HOURS AS ENHANCED BY NIGHTTIME COOLING.  
 
THE GLOBAL...REGIONAL AND HIGH RESOLUTION MODELS ARE HAVING A HARD  
TIME DEALING WITH THIS PATTERN...WITH NO TWO MODELS SHOWING  
PRECIPITATION IN THE SAME AREA. AS A RESULT...OUR GUIDANCE FOR THE  
NEXT THREE DAYS DEPENDS HEAVILY ON THE GFS/ECMWF GDI FORECAST AND  
THE LOW/MID LEVEL STEERING FLOW.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  
 

 
 
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