097  
FXCA20 KWBC 291148  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
647 AM EST WED NOV 29 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 29/06  
UTC: MID/UPPER LEVEL RIDGE REMAINS ACROSS THE EASTERN  
CARIBBEAN...WHERE IT GENERALLY FAVORS A FAIRLY STRONG TRADE WINDS  
CAP. A SHALLOW PLUME OF TROPICAL MOISTURE IS STREAMING UNDER THIS  
AXIS...CROSSING THE VIRGIN ISLES TO EASTERN PUERTO RICO EARLY THIS  
MORNING. THIS IS FORECAST TO QUICKLY MOVE ACROSS PUERTO RICO  
DURING THE DAY TODAY. ALTHOUGH HIGHER PWAT CONTENT ENVELOPS THE  
FORECAST AREA...LACKING UPPER LEVEL SUPPORT THIS IS TO ONLY  
TRIGGER LIGHT RAINFALL AMOUNTS OVER THE VIRGIN ISLES-EASTERN  
PUERTO RICO. MEASURABLE RAINFALL AMOUNTS WILL LIMIT TO INTERIOR  
PORTIONS OF PUERTO RICO IN LATE MORNING/EARLY AFTERNOON  
CONVECTION.  
 
MID LEVEL RIDGE IS FORECAST TO FLATTEN LATER TODAY/EARLY THURSDAY  
MORNING AS A SHORT WAVE TROUGH STREAMS TO THE NORTH. BUILDING  
RIDGE TO THE WEST IS TO THEN STEER ANOTHER SHORT WAVE PERTURBATION  
ACROSS THE FORECAST AREA LATER DURING THE WEEKEND. ALTHOUGH THE  
RIDGE TENDS TO WEAKEN...STRONG TRADE WINDS CAP IS EXPECTED TO HOLD  
THROUGH AT LEAST SATURDAY AFTERNOON. MEANWHILE...THIS IS TO  
CONTINUE FAVORING FAIR WEATHER CONDITIONS. AT LOW LEVELS AN  
ELONGATED FRONT MEANDERS OVER THE WESTERN ATLANTIC NORTH OF THE  
GREATER ANTILLES. THE MID LEVEL TROUGH STREAMING TO THE NORTH IS  
TO INTERACT WITH THIS BOUNDARY...INDUCING A FRONTAL LOW EAST OF  
THE BAHAMAS EARLY THIS AFTERNOON. THE LOW IS TO THEN TRACK FAR TO  
THE NORTH OF PUERTO RICO ON THURSDAY EVENING/EARLY FRIDAY MORNING.  
AS IT TRACKS TO THE NORTH...THE FRONTAL LOW IS TO INDUCE AN  
INVERTED TROUGH ACROSS THE EASTERN CARIBBEAN...WITH LOW LEVEL  
WINDS VEERING TO THE EAST-SOUTHEAST EARLY ON FRIDAY. THE  
SOUTHEASTERLY WINDS WILL PERSIST THROUGH SATURDAY MORNING. THIS IS  
TO SUSTAIN A MOIST ADVECTIVE PATTERN...WITH PWAT CONTENT OVER THE  
VIRGIN ISLES-PUERTO RICO INCREASING TO 1.50-1.75 INCHES.  
 
THE SURFACE LOW IS FORECAST TO GRADUALLY DEEPEN AS IT SLOWLY PULLS  
TO THE EAST-NORTHEAST DURING THE WEEKEND. A PREFRONTAL SHEAR LINE  
MOVES ACROSS THE VIRGIN ISLES-PUERTO RICO ON SATURDAY...WITH LOW  
LEVEL WINDS BACKING TO THE NORTHEAST DURING THE DAY. WANING  
SURFACE FRONT REACHES THE NORTHERN VI/PUERTO RICO ON SUNDAY. AS  
THE SHEAR LINE ENTERS THE FORECAST AREA IT WILL BE ACCOMPANIED BY  
SCATTERED SHALLOW CONVECTION...TO TRIGGER LIGHT TO MODERATE  
RAINFALL AMOUNTS ACROSS THE NORTHERN VI AND NORTHEAST PUERTO RICO  
ON SATURDAY. AS A COOL ADVECTIVE PATTERN ESTABLISHES ON  
SUNDAY...IT IS TO SUSTAIN AN INCREASE IN CONVECTION ACROSS  
NORTHERN PUERTO RICO AND THE NORTHERN VI...WITH MODELS SHOWING  
POTENTIAL FOR MODERATE RAINFALL AMOUNTS.  
 
DAVISON...WPC (USA)  
 

 
 
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