110  
FXCA20 KWBC 071129  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
628 AM EST THU DEC 07 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 07/06  
UTC: UNDER INFLUENCE OF A DEEPENING MID/UPPER LEVEL TROUGH OVER  
NORTH AMERICA...A HIGH AMPLITUDE RIDGE NOW EXTENDS FROM THE  
CENTRAL/EASTERN CARIBBEAN TO THE WESTERN ATLANTIC. AT 500 HPA THE  
MID LEVEL RIDGE CENTERS ON A CLOSED HIGH TO THE SOUTH-SOUTHEAST OF  
BERMUDA. THE RIDGE SUSTAINS THE RAPID INTENSIFICATION OF THE TRADE  
WINDS INVERSION ACROSS THE NORTHEAST CARIBBEAN...WITH A DRYER AIR  
MASS ENTRAINING FROM THE EAST. AT LOW LEVELS...AN  
ELONGATED/MEANDERING FRONT OVER THE NORTHERN LEEWARD-VIRGIN  
ISLES-PUERTO RICO BOUNDS THE SOUTHERN FRINGES OF A BROAD RIDGE  
OVER THE WESTERN ATLANTIC. THE RIDGE FAVORS A TIGHT  
GRADIENT...WITH BOUNDARY LAYER WINDS OVER THE NORTHEAST CARIBBEAN  
RANGING BETWEEN 18-21KT. AS A COOLER AIR MASS ADVECTS ACROSS THE  
WARMER WATERS OF THE WESTERN ATLANTIC...THIS FAVORS GENERATION OF  
TRADE WIND SHOWERS. BUT AS A DRYER AIR MASS ENTRAINS FROM THE  
EAST...THE SPATIAL AND TEMPORAL INTENSITY WILL GET LONGER AND LESS  
INTENSE EARLY IN THE PERIOD. FOCUS OF THE CONVECTION WILL THEN  
SHIFT TO CARIBBEAN WATERS EARLY THIS AFTERNOON.  
 
BROAD MID/UPPER LEVEL RIDGE IS TO THEN GRADUALLY WEAKEN WHILE  
YIELDING TO POLAR TROUGH ENTERING THE WESTERN ATLANTIC DURING THE  
WEEKEND/EARLY NEXT WEEK. ALTHOUGH THE RIDGE TENDS TO WEAKEN NORTH  
OF THE ISLANDS...OVER THE EASTERN CARIBBEAN IT WILL REMAIN STRONG  
ENOUGH TO HELP SUSTAIN A TRADE WINDS CAP ACROSS THE FORECAST AREA.  
THE LOW LEVEL RIDGE IS TO ALSO WEAKEN UNDER PRESSURE FROM POLAR  
FRONT ADVANCING ACROSS THE BASIN. AS THE RIDGE WEAKENS AND  
GRADIENT SLACKENS THE TRADES WILL DECREASE TO 10-15KT EARLY ON  
SUNDAY MORNING. THIS WILL BE ACCOMPANIED BY DISSIPATION OF THE OLD  
FRONTAL BOUNDARY AND SHARP DECREASE IN ACTIVITY TO THE SOUTH OF  
THE ISLANDS. LIGHTER WINDS ARE EXPECTED EARLY NEXT  
WEEK...GRADUALLY SHIFTING TO THE SOUTH-SOUTHEAST AS POLAR FRONT  
STALLS OVER THE TURKS/HAITI.  
 
OVER THE NEXT COUPLE OF DAYS THE INTENSIFYING TRADE WINDS CAP AND  
EROSION OF AVAILABLE MOISTURE IS TO LEAD TO A RAINFALL MINIMA WITH  
FAIR WEATHER CONDITIONS TO GENERALLY PREVAIL ACROSS THE ENTIRE  
FORECAST AREA. EARLY MORNING TRADE WIND SHOWERS WILL LIMIT TO THE  
VIRGIN ISLES-EASTERN PUERTO RICO...TO TRIGGER LIGHT RAINFALL  
AMOUNTS. LATE AFTERNOON DIURNAL CONVECTION WILL CONFINE TO WESTERN  
PUERTO RICO...BUT THIS IS TO ALSO FAVOR LIGHT RAINFALL AMOUNTS. ON  
SUNDAY...AS THE TRADES SLACKEN...MODELS SHOWING PATCHY CLOUD  
CLUSTERS TO ADVECT FROM THE EAST. BUT LACKING UPPER LEVEL SUPPORT  
ONLY EXPECTING LIGHT RAINFALL AMOUNTS.  
 
PECK...MS (JAMAICA)  
RIVAS...SENAMHI (PERU)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page