411  
FXCA20 KWBC 121153  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
752 AM EDT THU OCT 12 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM OCT 12/06  
UTC: MID-UPPER RIDGE CENTERS OVER PUERTO RICO WHILE A DEEP UPPER  
LOW IS EXITING THE REGION WHILE RETROGRESSING WESTWARD OVER  
CENTRAL CUBA. TO THE EAST...A WEAKER TROUGH EXTENDS AN AXIS ALONG  
50W IN THE ATLANTIC. AT LOW-LEVELS...A TROPICAL WAVE EXTENDS ALONG  
52-53W. IN PUERTO RICO AND THE USVI...FLOW IS FROM THE  
EAST-SOUTHEAST. AN INDUCED TROUGH EXTENDS NEAR 58W AND IS  
PROPAGATING IN THE TRADES TO THE SOUTHWEST. A PLUME OF ENHANCED  
MOISTURE CONTENT LIES JUST TO THE NORTH OF THE ISLANDS.  
 
THE FORECAST SHOWS THE MID-LEVEL RIDGE MEANDERING WESTWARD. THIS  
RIDGE ASSOCIATED WITH A WEAK SUBSIDENCE INVERSION AND DRY AIR AT  
MID-LEVELS...WHICH WILL BE SUFFICIENTLY STRONG TO DELAY THE ONSET  
OF DIURNAL THUNDERSTORMS...BUT NOT STRONG ENOUGH TO SUPPRESS THEM.  
THIS WILL ALLOW THE OCCURRENCE OF ISOLATED DIURNAL THUNDERSTORMS  
IN A DAILY BASIS. ALTHOUGH A TROUGH LIES TO THE EAST OF THE  
AFOREMENTIONED MID-UPPER RIDGE...THIS TROUGH IS FORECAST TO WEAKEN  
AS IT APPROACHES THE NORTHEASTERN CARIBBEAN...AND A NEW MID-LEVEL  
RIDGE IS FORECAST TO STRENGTHEN DURING THE WEEKEND. THIS WILL LEAD  
TO A FURTHER DRYING AFTER SATURDAY.  
 
IN THE MEAN TIME...AS THE LOW-LEVEL TROUGH APPROACHES FROM THE  
NORTHEAST...EXPECTING TRADES TO BACK FROM SOUTH EASTERLIES ON  
THURSDAY TO NORTH EASTERLIES ON FRIDAY. THIS WILL RELOCATE THE  
AREA PRONE TO AFTERNOON CONVECTION FROM NORTH WESTERN PUERTO RICO  
ON THURSDAY TO SOUTHWESTERN PUERTO RICO ON BOTH FRIDAY AND  
SATURDAY. IN TERMS OF ACCUMULATIONS...EXPECTING MAXIMA OF 1-1.5  
INCHES PER DAY IN AFTERNOON THUNDERSTORMS. IN THE SAN JUAN METRO  
AREA...UNDER THE NORTH EASTERLY TRADE WIND REGIME ON  
FRIDAY...EXPECTING AN INCREASE OF NIGHTTIME/EARLY MORNING SHOWERS  
ON FRIDAY-SATURDAY TO PRODUCE ACCUMULATIONS NEAR 0.2 INCHES. TRADE  
WIND SHOWERS ARE TO DECREASE IN COVERAGE ON SATURDAY INTO SUNDAY.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
GALVEZ...WPC (USA)  

 
 
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