221  
FXCA20 KWBC 101142  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
641 AM EST FRI NOV 10 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 10/06  
UTC: TUTT ALOFT CONTINUES TO RAPIDLY WEAKEN UNDER PRESSURE FROM  
DIGGING POLAR TROUGH OVER THE EASTERN USA-GULF OF MEXICO.  
ALSO...AS THE TROUGH DEEPENS TO THE WEST...CELL OF THE  
SUBEQUATORIAL RIDGE OVER THE EASTERN CARIBBEAN IS FORECAST TO  
BUILD NORTH INTO THE WESTERN ATLANTIC. THE UPPER RIDGE PATTERN IS  
TO THEN HOLD ITS GROUND DURING THE NEXT FOUR TO FIVE DAYS. THIS IS  
TO GENERALLY FAVOR AN UPPER DIVERGENT PATTERN ACROSS THE ENTIRE  
FORECAST AREA. AT 500 HPA...THE TUTT IS FORECAST TO WEAKEN AT A  
SLOWER PACE...WITH MID LEVEL CIRCULATION OVER THE CENTRAL  
CARIBBEAN TO SHEAR SHORT WAVE ENERGY OVER THE SUBEQUATORIAL RIDGE  
TO THE EAST AND ACROSS HISPANIOLA. THESE ARE TO GRAZE NORTHWEST  
PUERTO RICO FROM TIME-TO-TIME DURING THE NEXT THREE DAYS. THIS  
MIGHT BE ENOUGH TO PROVIDE SOME ENHANCEMENT TO DIURNAL CONVECTION  
ACROSS PUERTO RICO.  
 
AT 850 HPA...MEANDERING LOW OVER THE CENTRAL CARIBBEAN SUSTAINS A  
MOIST SOUTHEASTERLY FLOW ACROSS THE FORECAST AREA...WITH PWAT  
CONTENT BETWEEN HISPANIOLA AND THE VIRGIN ISLES PEAKING AROUND TWO  
INCHES. MODELS AGREE ON HIGH MOISTURE CONTENT TO PERSIST THROUGH  
AT LEAST SUNDAY AFTERNOON. THIS IS TO CONTINUE FAVORING MODERATE  
RAINFALL AMOUNTS WITH MOST INTENSE CLUSTERING OVER NORTHWEST  
PORTIONS OF PUERTO RICO. THE GLOBAL MODELS THEN FORECAST A DRYER  
AIR MASS TO ENTRAIN FROM THE EAST...A SOLUTION WELL SUPPORTED BY  
THE LATEST SATELLITE DERIVED PWAT ANALYSIS. BOTH THE GFS AND ECMWF  
GDI FORECASTS THEN SHOW A MORE STABLE AIR MASS TO ENVELOP THE  
FORECAST AREA ON MONDAY-TUESDAY...WITH FAIR WEATHER CONDITIONS  
EXPECTED ACROSS THE VIRGIN ISLES...SOUTHERN AND EASTERN PORTIONS  
OF PUERTO RICO. DIURNAL CONVECTION IS TO THEN CONFINE TO NORTHWEST  
PUERTO RICO IN MID AFTERNOON CONVECTION. BUT THESE ARE TO ONLY  
TRIGGER LIGHT TO MODERATE RAINFALL AMOUNTS.  
 
LATER IN THE WEEK MOISTURE CONTENT SURGES ACROSS THE FORECAST AREA  
AS A DEEP POLAR TROUGH MOVES ACROSS THE WESTERN ATLANTIC TO THE  
NORTHERN CARIBBEAN. THE FIRST COLD FRONT OF THE SEASON MIGHT REACH  
THE FORECAST AREA LATER ON FRIDAY/EARLY SATURDAY MORNING. STRONG  
MID/UPPER LEVEL SUPPORT WOULD LIKELY FAVOR HEAVY/ORGANIZED  
CONVECTION...WITH A COOLER ADVECTIVE PATTERN TO ESTABLISH DURING  
THE WEEKEND AS THE WINDS BACK TO THE NORTH.  
 
DAVISON...WPC (USA)  
 

 
 
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