092  
FXCA20 KWBC 161135  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
634 AM EST THU NOV 16 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 16/06  
UTC: DIGGING MID/UPPER LEVEL TROUGH DOMINATES THE FLOW ACROSS THE  
WESTERN-CENTRAL CARIBBEAN...WITH AXIS REACHING MAXIMUM AMPLITUDE  
ACROSS CENTRAL AMERICA ON FRIDAY. DURING THE WEEKEND IT IS TO THEN  
START A SLOW DECAYING PROCESS...WITH BROAD UPPER TROUGH WEAKENING  
TO A NARROW SHEAR AXIS OVER THE CENTRAL CARIBBEAN BEFORE LIFTING  
OVER BUILDING CELL OF THE SUBEQUATORIAL RIDGE TO THE EAST EARLY  
NEXT WEEK. A DIGGING POLAR TROUGH OVER THE GULF EARLY NEXT WEEK IS  
TO THEN FAVOR FURTHER INTENSIFICATION OF MID/UPPER LEVEL RIDGE  
ACROSS THE EASTERN CARIBBEAN. IN RESPONSE TO BUILDING RIDGE  
PATTERN...THE ENVIRONMENTAL CONDITIONS ARE TO GRADUALLY GROW  
HOSTILE FOR DEEP CONVECTION. THE GFS AND ECMWF THEN AGREE ON RAPID  
EROSION OF AVAILABLE MOISTURE LATER ON MONDAY. AT LOW LEVELS...A  
TROUGH EXTENDS SOUTH-SOUTHWEST FROM EASTERN CUBA/HAITI TO THE  
SOUTHERN CARIBBEAN-PANAMA. THIS FAVORS A MOIST SOUTHWESTERLY FLOW  
ACROSS THE CENTRAL CARIBBEAN INTO THE ISLAND OF HISPANIOLA-PUERTO  
RICO/VIRGIN ISLES. PWAT CONTENT CONTINUES TO PEAK AROUND 50MM. THE  
HIGH MOISTURE CONTENT IS FEEDING DIURNAL CONVECTION ACROSS THE  
FORECAST AREA. MOST INTENSE...HOWEVER...IS TO CONTINUE CLUSTERING  
ACROSS SOUTHERN HISPANIOLA AS ENHANCED BY THE UPPER LEVEL TROUGH.  
AS UPPER PATTERN EVOLVES...LOW LEVEL WINDS ARE TO SLOWLY BACK TO  
THE SOUTH-SOUTHEAST DURING THE WEEKEND...WITH PREVAILING  
EASTERLIES TO RETURN LATER ON MONDAY.  
 
ALTHOUGH MODELS FOLLOW SIMILAR EVOLUTION...THEY CONTINUE TO  
DISAGREE ON ITS IMPACT ACROSS THE FORECAST AREA. ADDING TO THE  
CHALLENGE...THICK CIRRUS CLOUDS BLOWING OFF FROM CONVECTION TO THE  
WEST WILL TEND TO DELAY ONSET OF DIURNAL CONVECTION ACROSS THE  
FORECAST AREA TO THE MID AND LATE AFTERNOON HOURS. THIS IS MOST  
LIKELY TO REMAIN AN ISSUE DURING THE NEXT TWO DAYS. MEANWHILE...IN  
A SOUTHWESTERLY STEERING FLOW...MOST ACTIVE WILL CLUSTER ACROSS  
NORTHERN PUERTO RICO. NIGHTTIME CONVECTION IS TO ALSO HAVE AN  
IMPACT ACROSS THE FORECAST AREA DURING THE NEXT COUPLE OF  
DAYS...WITH THE SOUTHWESTERLY STEERING WINDS DRIVING CONVECTION  
FORMING OVER AND SOUTH OF THE DOMINICAN REPUBLIC ACROSS PUERTO  
RICO. ON SATURDAY-SUNDAY...AS UPPER TROUGH WEAKENS...LESS DENSE  
UPPER CLOUD COVER WILL THEN ALLOW FOR NORMAL HEAT CYCLE TO  
PROPERLY FUNCTION.  
 
DAVISON...WPC (USA)  
 

 
 
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