640  
FXCA20 KWBC 031202  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
702 AM EST SUN DEC 03 2017  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 03/06  
UTC: BROAD MID/UPPER LEVEL TROUGH DOMINATES THE FLOW OVER THE  
CENTRAL-WESTERN ATLANTIC. A SHORT WAVE TROUGH EXITING FLORIDA ON  
MONDAY AFTERNOON IS TO GRADUALLY MERGE WITH BROAD TROUGH TO THE  
EAST ON TUESDAY. AS THEY COMBINE...AND THE GRADIENT TIGHTENS...THE  
GLOBAL MODELS AGREE ON RAPID INTENSIFICATION OF A SUBTROPICAL JET  
MAXIMA ROUNDING THE BASE OF THE LONG WAVE AXIS. FORECAST AREA WILL  
THEN LIE ON THE DIVERGENT RIGHT ENTRANCE REGION OF THE JET MAXIMA  
THROUGH WEDNESDAY AFTERNOON...WITH JET MAXIMA TO SLOWLY MEANDER  
AWAY LATER IN THE WEEK.  
 
AT LOW LEVELS...SURFACE FRONT LIES ACROSS THE WESTERN NORTH  
ATLANTIC...WITH BOUNDARY MEANDERING JUST NORTH OF THE FORECAST  
AREA ALONG 21N/22N TO THE BAHAMAS/CUBA. ON TUESDAY...A RIDGE ROLLS  
ACROSS THE EASTERN USA TO THE WESTERN ATLANTIC...TIGHTENING THE  
PRESSURE GRADIENT WHILE SUSTAINING A 20-25KT WINDS SURGE ACROSS  
THE NORTHERN CARIBBEAN ISLANDS. WINDY CONDITIONS ARE TO THEN  
PERSIST THROUGH THE END OF THE WORKWEEK. FURTHERMORE...THE  
BUILDING RIDGE AND SURGING TRADES ARE TO ALSO FAVOR REGENERATION  
OF A PREFRONTAL SHEAR LINE ACROSS THE FORECAST AREA ON TUESDAY.  
THIS DRIFTS OVER THE LEEWARD ISLES TO THE EASTERN CARIBBEAN LATER  
ON WEDNESDAY...WHILE SIMULTANEOUSLY DRIVING THE SURFACE FRONT OVER  
THE VIRGIN ISLES-PUERTO RICO BY MIDMORNING ON WEDNESDAY. UNDER  
INFLUENCE OF THE SHEAR LINE AND MEANDERING FRONT THE LOWER LEVEL  
WINDS ARE TO BACK FROM THE EAST-SOUTHEAST EARLY IN THE CYCLE TO  
THE EAST-NORTHEAST LATER ON TUESDAY/EARLY WEDNESDAY MORNING. THIS  
IS TO THEN FAVOR A COOL ADVECTIVE PATTERN ACROSS THE FORECAST  
AREA. COOL ADVECTION OVER THE WARMER WATERS OVER THE ATLANTIC WILL  
FAVOR A CONVECTIVELY UNSTABLE AIR MASS AND GENERATION OF TRADE  
WINDS SHOWERS...WHILE STRONG WINDS ACROSS THE ISLAND CHAIN WILL BE  
CONDUCIVE TO GENERATION OF STREAMERS. AS MOISTURE CONVERGES ACROSS  
THE FORECAST AREA...PWAT CONTENT IS TO GENERALLY RANGE BETWEEN  
1.50 TO 1.75 INCHES...WITH LOCALIZED MAXIMA OF NEARLY TWO INCHES  
AS THE SHEAR LINE STREAMS ACROSS THE FORECAST AREA EARLY ON  
WEDNESDAY MORNING.  
 
IN RESPONSE TO EVOLVING MESO-SYNOPTIC PATTERN...THE GLOBAL MODEL  
GUIDANCE GENERALLY AGREE ON WET CONDITIONS TO ESTABLISH BETWEEN  
TUESDAY-FRIDAY MORNING. BOTH EUROPEAN MODELS AND DETERMINISTIC GFS  
SOLUTION SHOW STORM TOTAL AMOUNTS RANGING BETWEEN 2-4 INCHES  
CLUSTERING BETWEEN NORTHEAST PUERTO RICO AND THE NORTHERN VIRGIN  
ISLES. THE WETTER SOLUTION IS WELL SUPPORTED BY THE LATEST CFS  
PREDICTION...WITH AN ATMOSPHERIC KELVIN WAVE MOVING ACROSS THE  
BASIN EARLY IN THE WEEK. THIS WILL BE FOLLOWED BY A WEAK MJO  
SIGNATURE...WITH ENVIRONMENTAL CONDITIONS LIKELY TO REMAIN  
FAVORABLE WELL INTO THE WEEKEND. THIS TAKEN INTO CONSIDERATION  
LEADS TO A HIGH CONFIDENCE IN THE FORECAST.  
 
DAVISON...WPC (USA)  
 

 
 
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