244  
FXCA20 KWBC 271147  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
646 AM EST WED DEC 27 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 27/06  
UTC: A MID LEVEL RIDGE EXTENDS WEST-TO-EAST FROM SOUTHERN MEXICO  
TO THE NORTHERN CARIBBEAN ISLES. THIS FAVORS AN ELEVATED  
INVERSION...WITH GOES 16 AIR MASS PRODUCT SHOWING A VERY DRY AIR  
MASS OVER THE NORTHEAST CARIBBEAN. NORTH OF THIS RIDGE...A POLAR  
TROUGH DOMINATES THE EASTERN USA-WESTERN ATLANTIC WHILE BOTTOMING  
OUT AROUND 30N. EAST OF THE RIDGE...A TUTT LOW OVER THE TROPICAL  
ATLANTIC EXTENDS A TROUGH ACROSS THE FRENCH/WINDWARD ISLES TO THE  
EASTERN CARIBBEAN. AT LOW LEVELS...BRISK EASTERLY TRADES  
PREVAIL...WITH MID LEVEL TUTT PATTERN INDUCING THE GENERATION OF  
EASTERLY WAVES THAT ARE STREAMING ACROSS THE NORTHEAST CARIBBEAN  
FROM TIME-TO-TIME. SHALLOW PLUME OF MOISTURE ACCOMPANY THESE  
PERTURBATIONS...WITH MOISTURE CONFINING TO ATMOSPHERE BELOW  
600-650 HPA.  
 
UNDER PRESSURE FROM POLAR TROUGH TO THE NORTH...MID LEVEL RIDGE  
PATTERN IS TO NEARLY COLLAPSE BY THE END OF THE WEEK. UPPER LEVEL  
INVERSION...HOWEVER...IS TO GENERALLY HOLD THROUGH THE  
WEEKEND/EARLY NEXT WEEK. AS THE RIDGE PATTERN WEAKENS...THE TUTT  
TO THE EAST AND SOUTH IS TO ALSO BECOME ILL ORGANIZED LATER DURING  
THE WEEKEND. MEANWHILE...THE TUTT IS TO CONTINUE FAVORING  
GENERATION OF EASTERLY WAVES THROUGHOUT THE SHORT RANGE  
PERIOD...WITH A COUPLE OF LOW/MID LEVEL PERTURBATIONS FORECAST TO  
STREAM ACROSS THE FORECAST AREA EARLY THIS AFTERNOON AND DURING  
THE DAY ON THURSDAY. PWAT CONTENT IS TO INCREASE...WITH BEST  
MOISTURE CONVERGENCE ON THURSDAY TO FAVOR A PWAT CONTENT OF  
1.30-1.60 INCHES. THESE ARE TO SUSTAIN SCATTERED CONVECTION ACROSS  
THE ENTIRE FORECAST AREA...WITH MOST ACTIVE TO CLUSTER ACROSS  
WESTERN INTERIOR PORTIONS OF PUERTO RICO IN MID TO LATE AFTERNOON  
CONVECTION ON THURSDAY. THIS IS TO RESULT IN 24 HRS RAINFALL  
AMOUNTS OF AROUND AN INCH. FOLLOWING THIS FEATURE...A DRYER AIR  
MASS IS TO THEN ENTRAIN ACROSS THE FORECAST AREA ON  
FRIDAY...RESULTING IN A LULL IN ACTIVITY AND MOSTLY FAIR WEATHER  
CONDITIONS. SHOWERS...IF ANY...WILL BE BRIEF AND TO ONLY TRIGGER  
LIGHT RAINFALL AMOUNTS OVER THE USVI-EASTERN PUERTO RICO DURING  
THE MORNING HOURS...AND ALONG THE CORDILLERA LATER IN THE DAY. THE  
NEXT EASTERLY WAVE ENTERS THE FORECAST AREA ON SATURDAY. BUT...ITS  
PWAT CONTENT IS NOT GOING TO BE AS HIGH AS THE ONE ON  
THURSDAY...WITH PWAT WITH THIS FEATURE TO PEAK AT NO HIGHER THAN  
1.25 INCHES. THUS ONLY EXPECTING LIGHT RAINFALL AMOUNTS IN PASSING  
SHOWERS TO AFFECT THE VIRGIN ISLES-EASTERN PUERTO RICO AND LIGHT  
TO MODERATE TO CONFINE TO WESTERN PUERTO RICO.  
 
DAVISON...WPC (USA)  
 

 
 
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