876  
FXCA20 KWBC 231137  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
637 AM EST TUE JAN 23 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 23/06  
UTC: A MID LEVEL HIGH OVER THE DOMINICAN REPUBLIC ANCHORS A RIDGE  
OVER THE WESTERN ATLANTIC-NORTHEAST CARIBBEAN ISLES. THIS FAVORS A  
CONVERGENT/SUBSIDENT PATTERN ACROSS THE FORECAST AREA. ALTHOUGH  
THE HIGH RELOCATES TO THE BAHAMAS AS THE WEEK WEARS ON...THE RIDGE  
IS TO PERSIST AND THE ASSOCIATED TRADE WINDS CAP IS TO HOLD WITH  
AN ELEVATED CAP INVERSION IS TO PREVAIL THROUGH THE END OF THE  
WEEK.  
 
AT LOW LEVELS...A HIGH OVER BERMUDA ANCHORS A RIDGE OVER THE  
WESTERN ATLANTIC/ NORTHERN CARIBBEAN ISLANDS. A WANING FRONT  
BOUNDS THE SOUTHERN FRINGES OF THIS RIDGE...WITH BOUNDARY  
EXTENDING JUST NORTH OF THE GREATER ANTILLES. LACKING UPPER LEVEL  
SUPPORT...THE FRONT IS TO DISSIPATE DURING THE NEXT DAY OR SO.  
FURTHERMORE...UNDER PRESSURE FROM POLAR FRONT/TROUGH EXITING THE  
USA...THE LOW LEVEL RIDGE IS TO WEAKEN AS IT RELOCATES TO THE  
CENTRAL ATLANTIC EARLY IN THE CYCLE. AS THE PRESSURE GRADIENT  
SLACKENS...LIGHTER EASTERLY TRADES ARE TO PREVAIL THROUGH  
MIDMORNING ON FRIDAY. THE LIGHTER WINDS WILL ALLOW SHALLOW  
MOISTURE TO POOL ACROSS THE NORTHEAST CARIBBEAN...WITH PWAT  
CONTENT FORECAST TO PEAK AROUND 1.50 INCHES ON TUESDAY AFTERNOON  
THROUGH EARLY THURSDAY MORNING. THIS WILL FEED DIURNAL CONVECTION  
OVER THE FORECAST AREA ON TUESDAY AND WEDNESDAY. DURING THIS  
PERIOD THE NAM AND REGIONAL HRWRF SHOW POTENTIAL FOR MODERATE  
RAINFALL AMOUNTS ACROSS WESTERN PUERTO RICO. A DRYER AIR MASS IS  
TO THEN ENTRAIN FROM THE EAST ON THURSDAY...WITH LIGHT AFTERNOON  
CONVECTION TO LIMIT TO THE CORDILLERA/INTERIOR PORTIONS OF PUERTO  
RICO.  
 
LATER IN THE WEEK...POLAR FRONT EXITING THE EASTERN USA MOVES JUST  
NORTH OF THE FORECAST AREA ON FRIDAY...WITH THE BOUNDARY STALLING  
ALONG 22N/23N. AS THE FRONT MOVES ACROSS THE WESTERN ATLANTIC THIS  
WILL BE PRECEDED BY A PREFRONTAL SHEAR LINE. NOTE THAT IN THIS  
CYCLE THE GFS FAVORS A MORE DYNAMIC FEATURE...WITH THE SHEAR LINE  
MOVING OVER PUERTO RICO ON FRIDAY AND OVER THE LEEWARD ISLES LATER  
IN THE DAY/EARLY SATURDAY MORNING. MODELS CONTINUE TO FORECAST A  
FAIRLY STRONG TRADE WINDS SURGE TO ACCOMPANY THE SHEAR LINE AS IT  
ENTERS THE FORECAST AREA...WITH 850 HPA WINDS PEAKING AT 30-35KT.  
THIS WILL FAVOR A COLD ADVECTIVE PATTERN THAT IS TO ENHANCE  
CONVECTIVE DEVELOPMENT ON FRIDAY TO SATURDAY. SCATTERED SHOWERS  
ARE EXPECTED DURING THE DAY...WITH MOST ACTIVE CONVECTION  
AFFECTING THE NORTHERN VI AND THE SAN JUAN METRO AREA/NORTHERN  
HALF OF PUERTO RICO.  
 
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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