369  
FXCA20 KWBC 191145  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
645 AM EST FRI JAN 19 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 19/06  
UTC: BROAD MID LEVEL RIDGE REMAIN DOMINANT FEATURE ACROSS THE  
NORTHEAST CARIBBEAN ISLANDS...WITH AXIS CENTERING ON A CLOSED HIGH  
THAT IS EXPECTED TO MEANDER BETWEEN PUERTO RICO-VIRGIN ISLES  
DURING THE NEXT FEW DAYS. THIS SUSTAINS AN ELEVATED TRADE WINDS  
CAP THAT IS FORECAST TO STRENGTHEN ON SATURDAY. THE  
MODELS...HOWEVER...DISAGREE ON HOW INTENSE THIS FEATURE IS GOING  
TO REMAIN...WITH THE GFS FAVORING A STRONGER RIDGE TO LAST THROUGH  
THE MEDIUM RANGE PERIOD. THE EUROPEAN MODEL FOLLOWS A SIMILAR  
EVOLUTION THROUGH MONDAY EVENING. IT THEN DISAGREES...FORECASTING  
THE RIDGE TO WEAKEN AS A SHORT WAVE TROUGH STREAMING ACROSS  
BERMUDA DEEPENS OVER THE WESTERN ATLANTIC. THUS...WHILE THE GFS  
FAVORS A STRONG TRADE WINDS CAP TO HOLD THROUGH THE MIDDLE OF NEXT  
WEEK...THE ECMWF IS FORECASTING THE CAP TO RELAX ITS FOOTHOLD  
ACROSS THE FORECAST AREA. DUE TO THE HIGH VARIABILITY IN  
SOLUTIONS...OVERALL FORECAST CONFIDENCE IS LOW BEYOND 84/96 HRS.  
 
AT LOW LEVELS...A BUILDING POLAR RIDGE CONTINUES TO ROLL ACROSS  
THE EASTERN USA TO THE WESTERN ATLANTIC. AS IT BUILDS EAST...THE  
RIDGE IS DRIVING A SURFACE FRONT ACROSS THE BAHAMAS-CUBA. THE  
BOUNDARY WILL CONTINUE TO THE EAST-SOUTHEAST DURING THE NEXT DAY  
OR SO...STALLING TO THE NORTH OF THE ISLANDS ALONG 22N EARLY ON  
SATURDAY MORNING. THE FRONT IS TO THEN REMAIN NEARLY STATIONARY  
WHILE GRADUALLY WEAKENING EARLY NEXT WEEK. UNDER INFLUENCE OF THE  
BROAD POLAR RIDGE TO THE NORTH...A PREFRONTAL SHEAR LINE WILL MOVE  
ACROSS THE DOMINICAN REPUBLIC LATER TODAY...WHERE IT IS TO MEANDER  
DURING THE NEXT FEW DAYS. THIS WILL BE THE FOCUS OF LOW LEVEL  
MOISTURE CONVERGENCE AND MOST ACTIVE CONVECTION DURING THE NEXT  
FEW DAYS.  
 
FURTHERMORE...THE RIDGE TO THE NORTH IS TO ALSO FAVOR A TIGHT  
GRADIENT ACROSS THE FORECAST AREA...WITH BRISK EAST-NORTHEASTERLY  
TRADES TO ENVELOP THE NORTHEAST CARIBBEAN EARLY ON SATURDAY. THE  
LOW LEVEL WINDS ARE FORECAST TO PEAK AT 20-25KT DURING THE  
WEEKEND-EARLY NEXT WEEK...MEANWHILE FAVORING A COOL ADVECTIVE  
PATTERN AND A DRYING TREND AS THE TRADE WINDS CAP STRENGTHENS ITS  
FOOTHOLD ACROSS THE FORECAST AREA DURING THE WEEKEND. THE STRONGER  
WINDS WILL FAVOR GENERATION OF TRADE WIND SHOWERS OVER THE WARMER  
WATERS NORTH OF THE ISLANDS AND STREAMERS ACROSS THE VIRGIN ISLES.  
THESE ARE TO PESTER THE FORECAST AREA FROM TIME-TO-TIME. EARLY IN  
THE CYCLE DIURNAL CONVECTION IS TO CLUSTER ACROSS WESTERN INTERIOR  
PORTIONS OF PUERTO RICO WHERE WE EXPECT MODERATE RAINFALL AMOUNTS  
DURING THE DAY TODAY. ON SATURDAY AND ONWARD...AS A DRYER AIR MASS  
ENTRAINS FROM THE EAST...EXPECTING LIGHT RAINFALL AMOUNTS ACROSS  
THE VIRGIN ISLES EASTERN/NORTHERN PUERTO RICO IN PASSING SHOWERS  
WITH MEASURABLE AMOUNTS CONFINING TO WESTERN INTERIOR PORTIONS OF  
THE ISLAND IN LATE AFTERNOON CONVECTION.  
 
DAVISON/GALVEZ...WPC (USA)  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page