575  
FXCA20 KWBC 261149  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
648 AM EST FRI JAN 26 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 26/06  
UTC: BUILDING POLAR RIDGE OVER THE WESTERN ATLANTIC/EASTERN USA IS  
DRIVING A POLAR FRONT ACROSS BERMUDA-THE BAHAMAS EARLY THIS  
MORNING. THIS TRIGGERED A PREFRONTAL SHEAR LINE THAT IS SURGING  
ACROSS THE DOMINICAN REPUBLIC. STRONG BOUNDARY LAYER WINDS  
ACCOMPANY THIS FEATURE...WITH SHIP REPORTS NEAR THE TURKS AND  
CAICOS SHOWING WINDS OF 25-30KT. THIS IS ENHANCING LOW LEVEL  
MOISTURE CONVERGENCE ALONG THE SHEAR LINE...WITH SATELLITE DERIVED  
PWAT ANALYSIS SHOWING MOISTURE POOLING ACROSS NORTHERN HISPANIOLA.  
HOWEVER...PERSISTENT MID LEVEL RIDGE AND ASSOCIATED TRADE WINDS  
CAP CONTINUES TO INHIBIT DEEP CONVECTION IN ASSOCIATION WITH THIS  
FEATURE. AHEAD OF THE SHEAR LINE...A FRESH NORTHEASTERLY FLOW AND  
A PWAT MINIMA ENVELOP THE FORECAST AREA.  
 
THE SURFACE FRONT IS TO SAG JUST NORTH OF THE FORECAST AREA EARLY  
ON SATURDAY MORNING...WHILE TRAILING ACROSS THE BAHAMAS TO THE  
FLORIDA PENINSULA. BOUNDARY IS TO REMAIN NEARLY STATIONARY THROUGH  
EARLY NEXT WEEK...WHEN IT IS EXPECTED TO FRONTOLIZE. THE  
PREFRONTAL SHEAR LINE MOVES ACROSS THE MONA PASSAGE TO NORTHWEST  
PUERTO RICO THIS MORNING...PULLING ACROSS SAN JUAN BY 18-21 UTC  
TODAY. THIS WILL BE ACCOMPANIED BY A 20-30KT WIND SURGE...COLD  
ADVECTION AND A LOW LEVEL CONVERGENT PATTERN. THE SHEAR LINE  
ENTERING THE SAN JUAN METRO AREA WILL COINCIDE WITH PERIOD OF MAX  
HEATING...ENHANCING CONVECTIVE INSTABILITY AS THIS FEATURE CROSSES  
THE ISLAND. THE SHEAR LINE IS THEN FORECAST TO MEANDER BETWEEN THE  
VIRGIN ISLES-EASTERN PUERTO RICO THROUGH SATURDAY MORNING...MOVING  
FARTHER EAST ACROSS THE ISLAND CHAIN LATER IN THE DAY. AS IT PULLS  
AWAY AND RIDGE STRENGTHENS OVER THE ATLANTIC THE LOW/MID LEVEL  
WINDS ARE TO GRADUALLY VEER TO THE EAST DURING THE WEEKEND. STRONG  
BOUNDARY LAYER WINDS ARE TO PERSIST THROUGH MONDAY...TO CONTINUE  
FAVORING A COOL ADVECTIVE PATTERN AND GENERATION OF TRADE WIND  
SHOWERS ACROSS THE VIRGIN ISLES INTO PUERTO RICO.  
 
UNDER THE INFLUENCE OF THE WIND SURGE/SHEAR LINE CONVERGENCE AND  
ASSOCIATED COLD ADVECTIVE PATTERN...EXPECTING A MORE SEASONAL  
PATTERN OF TRADE WIND SHOWERS TO AFFECT PUERTO RICO AND THE VIRGIN  
ISLES DURING THE NEXT FEW DAYS. FURTHERMORE... THE STRONGER  
EASTERLY TRADES ARE TO ALSO FAVOR GENERATION OF STREAMERS THAT ARE  
TO CONVERGE ACROSS VIEQUES...CULEBRA AND EASTERN PORTIONS OF  
PUERTO RICO. THESE WILL COMBINE WITH PERSISTENT COOL ADVECTIVE  
PATTERN AND MEANDERING SHEAR LINE TO LIKELY FAVOR MODERATE TO  
HEAVY RAINFALL AMOUNTS ACROSS THE VIRGIN ISLES AND EASTERN PUERTO  
RICO/SAN JUAN METRO AREA THIS AFTERNOON THROUGH SATURDAY MORNING.  
LIGHT TO MODERATE RAINFALL AMOUNTS ARE THEN EXPECTED THROUGHOUT  
THE WEEKEND/EARLY NEXT WEEK...WITH MOST ACTIVE CLUSTERING ACROSS  
THE EASTERN THIRD OF PUERTO RICO...WITH LOCALIZED MAXIMA OVER  
SIERRA DE LUQUILLO/EL YUNQUE.  
 
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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