120  
FXCA20 KWBC 011101  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
700 AM EDT WED NOV 01 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 01/06  
UTC: FORECAST AREA LIES ON THE CONVERGENT SIDE OF A MID/UPPER  
LEVEL RIDGE THAT EXTENDS OVER THE SOUTHWEST ATLANTIC-CARIBBEAN  
BASIN...WITH AXIS CENTERING ON A CLOSED HIGH OVER THE TURKS AND  
CAICOS/SOUTHEAST BAHAMAS. DOWNSTREAM FROM THIS AXIS...A TUTT LIES  
JUST EAST OF THE ISLAND CHAIN TO THE GUIANAS. AT LOW  
LEVELS...BROAD RIDGE OVER THE EASTERN USA/WESTERN ATLANTIC  
SUSTAINS A LONG FETCH NORTHEASTERLY FLOW ACROSS THE NORTHEAST  
CARIBBEAN ISLES. THIS FAVORS THE ADVECTION OF A COOLER/DRYER AIR  
MASS... WHICH IN COMBINATION WITH MID LEVEL CAP INVERSION RESULTS  
IN EROSION OF AVAILABLE MOISTURE. ALSO AT LOW LEVELS...THE TUTT TO  
THE EAST INDUCED A PERTURBATION IN THE NORTHEASTERLY TRADES WITH  
AXIS ALONG 61W/62W AND NORTH OF ANTIGUA EARLY THIS MORNING. THIS  
WAVE IS NOT STRONG ENOUGH TO OVERCOME NEGATIVE INFLUENCE OF  
MID/UPPER LEVEL RIDGE PATTERN...AND AS A RESULT IT ONLY FAVORS  
ISOLATED TO SCATTERED SHALLOW CONVECTION.  
 
POLAR TROUGHS STREAMING ACROSS THE USA ARE TO PRESS AGAINST BROAD  
MID/UPPER LEVEL RIDGE OVER THE BASIN/SOUTHWEST ATLANTIC. UNDER  
PRESSURE FROM THESE PERTURBATIONS THE RIDGE IS TO GRADUALLY WEAKEN  
THROUGH SATURDAY. AS THE RIDGE ERODES...CLOSED HIGH MOVES FROM THE  
TURKS/SOUTHEAST BAHAMAS TO CENTRAL MEXICO EARLY ON FRIDAY MORNING.  
DURING THE WEEKEND...A TROUGH IS TO THEN DEEPEN ACROSS THE  
BAHAMAS-CUBA TO THE WESTERN CARIBBEAN. AS THE PATTERN  
EVOLVES...TRADE WINDS CAP WILL GRADUALLY RELAX ITS FOOTHOLD ACROSS  
THE FORECAST AREA DURING THE WEEKEND. PWAT CONTENT IS TO GRADUALLY  
INCREASE TO 1.50-1.75 INCHES LATER ON SATURDAY.  
 
AT LOW LEVELS...THE DEEP LAYER NORTHEASTERLY WINDS ARE TO PERSIST  
THROUGH FRIDAY MORNING...MEANWHILE SUSTAINING A COOL ADVECTIVE  
PATTERN. THIS WILL FAVOR GENERATION OF EARLY MORNING SHALLOW  
CONVECTION ACROSS NORTHERN PUERTO RICO AND THE NORTHERN VIRGIN  
ISLES. IN THIS PATTERN...MEASURABLE AMOUNTS OVER THE NEXT COUPLE  
OF DAYS ARE TO CONFINE TO SOUTHWEST PUERTO RICO AND EL YUNQUE  
RAINFOREST. SLIGHTLY HIGHER AMOUNTS ARE POSSIBLE EARLY ON THURSDAY  
AS THE TUTT INDUCED PERTURBATION STREAMS ACROSS THE VIRGIN ISLES.  
DURING THE LATE MORNING/AFTERNOON HOURS THE WAVE WILL THEN MOVE  
ACROSS PUERTO RICO...WITH MOST ACTIVE CONVECTION EXPECTED ACROSS  
WESTERN INTERIOR PORTIONS OF THE ISLANDS. PREVAILING EASTERLY  
TRADES RETURN TO THE FORECAST AREA ON FRIDAY...AND ON SATURDAY TO  
SUNDAY THEY VEER TO THE SOUTHEAST. THIS WILL FAVOR A MOIST  
ADVECTIVE PATTERN...THAT IN COMBINATION WITH WANING TRADE WINDS  
CAP WILL ALLOW FOR DEEPER MOISTURE TO POOL ACROSS THE FORECAST  
AREA. THUS...RESULTING IN A HIGHER PROBABILITY FOR MODERATE  
RAINFALL AMOUNTS DURING THE WEEKEND.  
 
GUY...NMS (BELIZE)  
PECK...MS (JAMAICA)  
DAVISON...WPC (USA)  
 

 
 
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