534  
FXCA20 KWBC 181156  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
656 AM EST SAT NOV 18 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 18/06  
UTC: A MID/UPPER LEVEL TROUGH OVER THE WESTERN CARIBBEAN IS  
VENTING DEEP CONVECTION IN ASSOCIATION WITH MEANDERING LOW LEVEL  
TROUGH TO THE EAST. THE TROUGH EXTENDS FROM HAITI/WINDWARD PASSAGE  
TO THE GULF OF URABA/NORTHERN HONDURAS. THIS FAVORS A DEEP LAYER  
SOUTHWESTERLY FLOW ACROSS THE FORECAST AREA...WITH BROAD AREA OF  
PWAT CONTENT OF TWO INCHES ENVELOPING THE CENTRAL  
CARIBBEAN-HISPANIOLA/PUERTO RICO. EMBEDDED IN THIS FLOW...THE  
REMNANTS OF AN MCS THAT FORMED SOUTH-SOUTHEAST OF THE DOMINICAN  
REPUBLIC ARE STREAMING ACROSS PUERTO RICO EARLY THIS  
MORNING...FAVORING ORGANIZED HEAVY CONVECTION.  
 
UPPER LEVEL TROUGH OVER THE WESTERN CARIBBEAN IS TO RAPIDLY LIFT  
TO THE NORTHEAST EARLY IN THE CYCLE AS A HIGH AMPLITUDE POLAR  
TROUGH DEEPENS ACROSS THE USA TO THE GULF OF MEXICO. AS THE TROUGH  
WEAKENS...THE ENVIRONMENTAL CONDITIONS WILL NOT BE AS CONDUCIVE  
FOR MCS TO CONTINUE FORMING OVER/SOUTH OF HISPANIOLA.  
INSTEAD...DIURNAL CONVECTION WILL TAKE CENTER STAGE OVER PUERTO  
RICO AND SAINT CROIX...WITH VEERING WINDS WITH HEIGHT TO RESULT IN  
ENOUGH SHEAR FOR ORGANIZED DEEP CONVECTION TO DEVELOP. IN A DEEP  
LAYER SOUTHWESTERLY FLOW...MOST INTENSE IS TO CLUSTER ACROSS THE  
SAN JUAN METRO AREA DURING THE AFTERNOON HOURS...WITH PEAK IN  
ACTIVITY EXPECTED BETWEEN 17-00 UTC. ON SUNDAY...AS THE LOW LEVEL  
WINDS BACK TO THE SOUTHEAST...FOCUS OF THE HEAVY CONVECTION SHIFTS  
TO WESTERN INTERIOR PORTIONS OF PUERTO RICO...WITH MODERATE TO  
HEAVY CONVECTION EXPECTED ACROSS THE GUAJATACA BASIN. NOTE THAT  
THIS IS MORE INTENSE AND LONGER LASTING THAN WHAT WE PREVIOUSLY  
ANTICIPATED.  
 
ON MONDAY AND ONWARD...MODELS SHOWING GRADUAL DRYING TREND AS  
MID/UPPER LEVEL CELL OF THE SUBEQUATORIAL RIDGE STRENGTHENS ITS  
FOOTHOLD ACROSS THE FORECAST AREA AND EASTERLY TRADES RETURN TO  
THE FORECAST AREA. UNDER INFLUENCE OF THE MID LEVEL RIDGE A  
STRONG INVERSION TO SET AT 800/850 HPA LATER ON MONDAY/EARLY ON  
TUESDAY MORNING...WITH LIGHT DIURNAL CONVECTION TO LIMIT TO EL  
YUNQUE RAINFOREST AND WEST COAST OF PUERTO RICO. OTHERWISE...FAIR  
WEATHER CONDITIONS ARE TO PREVAIL.  
 
DAVISON...WPC (USA)  
 

 
 
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