273  
FXCA20 KWBC 111146  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
645 AM EST SAT NOV 11 2017  
 
LAST NO AMENDS...NEXT ON MONDAY NOV 13 AT 1200 UTC.  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV 11/06  
UTC: AT UPPER LEVELS...BROAD CELL OF THE SUBEQUATORIAL RIDGE NOW  
DOMINATES THE FLOW ACROSS THE CENTRAL/EASTERN CARIBBEAN INTO THE  
WESTERN ATLANTIC. AT 500 HPA THIS REFLECTS AS AN ILL ORGANIZED  
RIDGE OVER THE EASTERN CARIBBEAN...WITH SOME INTENSIFICATION  
POSSIBLE ON TUESDAY AHEAD OF A HIGH AMPLITUDE POLAR TROUGH  
ENTERING THE WESTERN ATLANTIC. THE MID LEVEL RIDGE IS TO INITIALLY  
FAVOR A WEAK TRADE WINDS CAP...FORECAST TO STRENGTHENS ON  
MONDAY-TUESDAY. UNDER INFLUENCE OF WANING MID LEVEL TROUGH TO THE  
WEST...POOL OF DEEP TROPICAL MOISTURE REMAINS ACROSS THE FORECAST  
AREA...WITH PWAT CONTENT OF TWO INCHES PER SATELLITE DERIVED  
ANALYSIS. AT LOW LEVELS...BRISK EAST-SOUTHEAST TRADE WINDS  
PREVAIL. THROUGH SUNDAY EVENING THE PWAT CONTENT IS FORECAST TO  
DROP TO AROUND 1.25-1.50 INCHES AS THE TRADE WINDS CAP STRENGTHENS  
AND A DRYER AIR MASS ENTRAINS FROM THE EAST. LOW PWAT CONTENT IS  
TO THEN PERSIST THROUGH AT LEAST WEDNESDAY MORNING. IN RESPONSE TO  
EVOLVING MID/UPPER LEVEL PATTERN GLOBAL MODELS MAINTAIN PREVIOUSLY  
NOTED TREND...WITH CONVECTION ACROSS THE FORECAST AREA EBBING  
THROUGH MONDAY. THIS WILL BE ACCOMPANIED BY A DECREASE IN CLOUD  
COVER AND WARMER TEMPERATURES. MEANWHILE...SCATTERED SHOWERS ARE  
TO BUILD ACROSS THE FORECAST AREA DURING THE DAY TODAY...WITH MOST  
ACTIVE CLUSTERING ACROSS NORTHWEST PUERTO RICO DURING THE  
AFTERNOON HOURS. ON SUNDAY GDI FORECAST SHOWS DECREASE IN ACTIVITY  
ACROSS EASTERN PUERTO RICO AND THE VIRGIN ISLES...WITH BETTER  
CHANCE FOR DEEP CONVECTION OVER NORTHWEST PORTIONS OF THE ISLAND.  
ON MONDAY-TUESDAY DIURNAL CONVECTION IS TO GENERALLY CONFINE TO  
NORTHWEST PORTIONS OF PUERTO RICO IN MID AFTERNOON CONVECTION.  
 
LONG RANGE GUIDANCE SHOWS MID/UPPER LEVEL POLAR TROUGH STREAMING  
ACROSS THE WESTERN NORTH ATLANTIC...WITH BASE OF THE UPPER LEVEL  
TROUGH BOTTOMING OUT ACROSS NORTHERN HISPANIOLA ON  
FRIDAY-SATURDAY. UNDER INFLUENCE OF THIS TROUGH THE LOW LEVEL  
WINDS ARE TO VEER TO THE SOUTHWEST AND THE TRADE WINDS CAP IS TO  
WEAKEN BY MIDDAY ON WEDNESDAY. DEEPER MOISTURE IS TO ONCE AGAIN  
POOL ACROSS THE FORECAST AREA...WITH PWAT CONTENT PEAKING AROUND  
TWO INCHES. THE ASSOCIATED SURFACE FRONT THEN MEANDERS JUST NORTH  
OF THE FORECAST AREA LATER IN THE WEEK. IN CONTRAST TO PREVIOUS  
FORECAST THE MODELS NO LONGER SHOW FROPA...WITH BOUNDARY  
DISSIPATING AS IT MEANDERS TO THE NORTH ON SATURDAY-SUNDAY.  
MEANWHILE...AS THE LOW/MID LEVEL WINDS BACK TO THE SOUTHWEST AHEAD  
OF THE POLAR TROUGH ON WEDNESDAY...AND PWAT CONTENT SURGES ACROSS  
THE FORECAST AREA...THERE IS AN ENHANCED RISK OF MODERATE TO HEAVY  
RAINFALL AMOUNTS ACROSS PUERTO RICO...WITH A HIGHER RISK ON THE  
SAN JUAN METRO AREA LATER IN THE WEEK.  
 
DAVISON...WPC (USA)  
 

 
 
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