430  
FXCA20 KWBC 241059  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
658 AM EDT MON APR 24 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APRIL  
24/06 UTC: POLAR TROUGH OVER THE EASTERN USA/GULF OF MEXICO IS  
SLOWLY PRESSING AGAINST A RIDGE TO THE EAST. THE MID/UPPER LEVEL  
TROUGH IS FORECAST TO GRADUALLY LIFT OVER THIS AXIS OVER THE NEXT  
DAY OR SO. AS IT STREAMS ACROSS THE FORECAST AREA...THIS IS TO  
SUSTAIN DEEP LAYER CONVECTIVE INSTABILITY AND MESO-SYNOPTIC  
FORCING. A JET MAXIMA EXITS JUST SOUTH OF PONCE ON TUESDAY. THIS  
WILL FAVOR A DIVERGENT PATTERN ALOFT THAT IS TO VENT DEEP  
CONVECTION DURING THE DAY. AT LOW LEVELS...ASSOCIATED FRONT  
MEANDERS OVER THE WESTERN ATLANTIC...WHILE A RIDGE TO THE EAST  
SETTLES OVER THE CENTRAL ATLANTIC. THE RIDGE SUSTAINS A MOIST  
SOUTHEASTERLY FLOW ACROSS THE LESSER ANTILLES...WITH MOISTURE  
CONVERGING OVER PUERTO RICO/VIRGIN ISLES. THE GLOBAL MODEL  
GUIDANCE DIVERGE ON WHAT IMPACT THIS IS GOING TO HAVE ACROSS THE  
FORECAST AREA...WITH THE ECMWF FAVORING MOST ACTIVE JUST NORTH OF  
THE ISLANDS...WHILE THE UKMET AND GFS SHOW MORE WIDESPREAD  
CONVECTION ACROSS THE FORECAST AREA.  
 
CONSIDERING HIGH MOISTURE CONTENT...WITH PWAT OF NEARLY TWO  
INCHES...WE ARE LEANING TOWARDS THE WETTER MODELS. DURING THE DAY  
TODAY THIS IS TO FAVOR SCATTERED CONVECTION...WITH GRADUAL  
INCREASE EXPECTED ON TUESDAY AS UPPER JET DYNAMICS BECOME MORE  
FAVORABLE. OVER THE NEXT COUPLE OF DAYS...IN A SOUTHEASTERLY  
STEERING FLOW...THE MOST INTENSE IS LIKELY TO CLUSTER ACROSS  
NORTHWEST PUERTO RICO BY MIDDAY/EARLY AFTERNOON...WITH SECONDARY  
MAXIMA ACROSS THE VIRGIN ISLES/EASTERN PUERTO RICO DURING THE  
AFTERNOON HOURS. STREAMERS FORMING OVER SAINT CROIX ARE LIKELY TO  
AFFECT SOUTHEAST PORTIONS OF PUERTO RICO. RAINFALL MAXIMA WILL  
LIKELY PEAK AROUND AN INCH FOR THE DAY TODAY...AND UNDER STRONGER  
FORCING ON TUESDAY EXPECTING LOCALIZED MAXIMA OF 3-4 INCHES.  
 
PREVAILING EASTERLY TRADES RETURN TO THE FORECAST AREA ON  
WEDNESDAY AS THE POLAR TROUGH/FRONT LIFT TO THE NORTH-NORTHEAST  
AND THE RIDGE BUILDS WEST ACROSS THE ATLANTIC. THIS IS TO  
GRADUALLY STRENGTHEN THE TRADE WINDS CAP...SUSTAINING EROSION OF  
AVAILABLE MOISTURE. DURING THAT PERIOD LIGHT COASTAL CONVECTION IS  
TO AFFECT EASTERN PORTIONS OF PUERTO RICO...WHILE MEASURABLE  
AMOUNTS CONFINE TO WESTERN INTERIOR PORTIONS OF THE ISLAND.  
 
GAJADHAR...SLMS (SAINT LUCIA)  
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)  
DAVISON/GALVEZ...WPC (USA)  

 
 
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