079  
FXCA20 KWBC 301144  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
644 AM EST TUE JAN 30 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 30/06  
UTC: MID/UPPER PATTERN CONTINUES TO EVOLVE UNDER PRESSURE FROM  
POLAR TROUGH MOVING OVER THE WESTERN ATLANTIC. BY THE END OF THE  
DAY THE TROUGH IS TO ENVELOP AREA NORTH OF 22N/23N. AS THE TROUGH  
SETTLES...A RIDGE EXTENDING FROM THE CARIBBEAN TO THE WESTERN  
ATLANTIC IS TO GRADUALLY FLATTEN. REMNANTS OF THE RIDGE ARE TO  
THEN CONFINE TO THE CARIBBEAN BASIN. THIS PATTERN IS TO GENERALLY  
PERSIST THROUGH THE WEEKEND/EARLY NEXT WEEK. AS THE MID LEVEL  
RIDGE SETTLES OVER THE CARIBBEAN...THE TRADE WINDS CAP OVER THE  
NORTHEAST CARIBBEAN ISLES IS FORECAST TO STRENGTHEN. THE MODELS  
FORECAST THE INVERSION TO RAPIDLY DROP FROM 600/650 HPA DURING THE  
DAY TODAY TO AROUND 750/800 HPA ON WEDNESDAY. THE STRONG TRADE  
WINDS CAP IS TO THEN PERSIST THROUGH THE WEEKEND. UNDER INFLUENCE  
OF THE STRENGTHENING TRADE WINDS CAP EXPECTING THE RAPID EROSION  
OF AVAILABLE MOISTURE FROM THE EAST-NORTHEAST. A PWAT MINIMA IS TO  
THEN ENVELOP THE FORECAST AREA BETWEEN TUESDAY MORNING AND LATE  
EVENING ON THURSDAY.  
 
AT LOW LEVELS...BROAD RIDGE OVER THE CENTRAL ATLANTIC CONTINUES TO  
CRUMBLE UNDER PRESSURE FROM POLAR FRONT STREAMING ACROSS THE  
WESTERN ATLANTIC/BAHAMAS. AS THE RIDGE WEAKENS AND GRADIENT  
SLACKENS THE BOUNDARY LAYER WINDS WILL DECREASE FROM 15-20KT EARLY  
IN THE CYCLE TO 10-15KT LATER THIS AFTERNOON...WITH LIGHTER WINDS  
POSSIBLE ON WEDNESDAY. ALTHOUGH THE RIDGE COLLAPSES...THE SURFACE  
FRONT IS FORECAST TO BOTTOM OUT NORTH OF 24N ON  
WEDNESDAY-THURSDAY...TO WEAKEN AS IT MEANDERS JUST NORTH OF THE  
FORECAST AREA LATER IN THE WEEK. UNDER INFLUENCE OF A BROAD POLAR  
RIDGE TO THE NORTH OF THIS BOUNDARY...A FRESH NORTHEASTERLY FLOW  
ESTABLISHES ACROSS THE FORECAST AREA ON WEDNESDAY.  
THIS...HOWEVER...WILL BE SHORT LIVED...WITH THE PREVAILING  
EASTERLY TRADES RETURNING TO THE NORTHEAST CARIBBEAN ON  
THURSDAY-FRIDAY. ON FRIDAY-MONDAY...AS THE WANING FRONT MEANDERS  
JUST NORTH OF THE ISLANDS...THE MODELS AGREE ON SHALLOW CLOUD  
CLUSTERS ALONG THIS BOUNDARY TO ADVECT ACROSS THE FORECAST AREA  
FROM TIME TO TIME.  
 
ELEVATED CAP INVERSION AND BRISK EASTERLY TRADES WILL FAVOR  
SCATTERED SHOWERS DURING THE DAY TODAY. BUT AS THE WINDS START TO  
WEAKEN DURING THE DAY...SHOWERS WILL GRADUALLY BECOME MORE SPARSE  
AND LESS INTENSE. MOST INTENSE IS TO CLUSTER ACROSS EL  
YUNQUE/SIERRA DE LUQUILLO AND WESTERN INTERIOR PORTIONS OF PUERTO  
RICO. ON WEDNESDAY AND THURSDAY...AS A STRONG TRADE WINDS CAP  
SETTLES ACROSS THE FORECAST AREA EXPECTING FAIR WEATHER CONDITIONS  
TO PREVAIL. RAINFALL...IF ANY...WILL LIMIT TO THE CORDILLERA AND  
EL YUNQUE IN MID/LATE AFTERNOON CONVECTION. AN INCREASE IN CLOUD  
COVER ON FRIDAY-MONDAY WILL THEN FAVOR ANOTHER ROUND OF SHOWERS  
ACROSS THE ENTIRE FORECAST AREA. BUT LACKING THE DEPTH OF THE  
LATEST EVENT ONLY EXPECTING LIGHT RAINFALL AMOUNTS IN PASSING  
SHOWERS. MEASURABLE AMOUNTS WILL LIMIT TO NORTHEAST PUERTO RICO  
AND WESTERN INTERIOR PORTIONS OF THE ISLAND.  
 
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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