621  
FXCA20 KWBC 101141  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
641 AM EST WED JAN 10 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JAN 10/06  
UTC: AT 500 HPA...A HIGH NEAR 25N 64W EXTENDS A RIDGE TO THE  
NORTHEAST CARIBBEAN. SOUTH OF THIS AXIS...AN ELONGATED TROUGH  
STRETCHES ACROSS THE WINDWARD ISLES TO THE SOUTHEAST CARIBBEAN.  
THIS IS TO SHEAR A SHORT WAVE VORTEX/INVERTED TROUGH THAT IS  
EXPECTED TO PROPAGATE ACROSS THE EASTERN CARIBBEAN OVER THE NEXT  
DAY OR SO. AT LOW LEVELS... BUILDING RIDGE TO THE NORTH IS TO  
DOMINATE THE FLOW ACROSS THE EASTERN CARIBBEAN DURING THE NEXT FEW  
DAYS. THIS WILL FAVOR A BRISK EASTERLY FLOW...WITH 925/950 HPA  
WINDS FORECAST TO PEAK AROUND 25-30KT. THE STRONGER WINDS WILL  
LIKELY FAVOR GENERATION OF STREAMERS ACROSS THE NORTHERN  
LEEWARD/VIRGIN ISLES...TO PESTER EASTERN PUERTO RICO/SAN JUAN  
METRO AREA FROM TIME-TO-TIME. FURTHERMORE...EMBEDDED IN THE  
EASTERLY TRADES...A PLUME OF SHALLOW MOISTURE IS ADVECTING ACROSS  
THE NORTHEAST CARIBBEAN...WITH PWAT CONTENT PEAKING AROUND  
40-45MM. THE HIGHER MOISTURE CONTENT IS EXPECTED TO PERSIST  
THROUGH LATE AFTERNOON HOURS ON THURSDAY. MEANWHILE...THIS WILL  
FEED DIURNAL CONVECTION ACROSS PUERTO RICO...WITH GLOBAL MODELS  
SHOWING MOST ACTIVE CLUSTERING ON THE EASTERN SIDE OF THE ISLAND.  
HOWEVER...DIURNAL CONVECTION IS TO ALSO BUILD ACROSS INTERIOR  
PORTIONS OF PUERTO RICO DURING THE AFTERNOON HOURS...WHERE WE  
EXPECT MODERATE RAINFALL AMOUNTS. OVER THE VIRGIN ISLES PASSING  
SHOWERS ARE TO DOMINATE THROUGH THURSDAY AFTERNOON...TO GENERALLY  
FAVOR LIGHT/LOCALLY MODERATE RAINFALL AMOUNTS. ON FRIDAY FAIR  
WEATHER CONDITIONS ARE TO PREVAIL AS A DRYER AIR MASS ENTRAINS  
FROM THE EAST...WITH LIGHT CONVECTION LIMITING TO INTERIOR  
PORTIONS OF PUERTO RICO. ON SATURDAY A SECONDARY PLUME OF MOISTURE  
ADVECTS ACROSS THE FORECAST AREA...WITH GDI FORECAST FOR THIS  
PERIOD SHOWING BEST INSTABILITY ACROSS WESTERN INTERIOR PORTIONS  
OF PUERTO RICO. THIS IS TO TRIGGER MODERATE/LOCALLY  
HEAVY...RAINFALL AMOUNTS.  
 
SIMULTANEOUSLY...THE PERSISTENT MID LEVEL RIDGE NORTH OF THE  
ISLANDS IS TO STEER A TROUGH TO THE SOUTHWEST ACROSS THE CENTRAL  
ATLANTIC. EARLY DURING THE WEEKEND IT REACHES THE NORTHEAST  
CARIBBEAN...WHILE ANCHORING ON A CLOSED LOW TO THE NORTHEAST OF  
THE LEEWARD ISLES. THIS WILL THEN PERSIST THROUGH EARLY NEXT  
WEEK...WEAKENING ON TUESDAY-WEDNESDAY AS THE MID LEVEL RIDGE  
INTENSIFIES ACROSS THE EASTERN CARIBBEAN. ALTHOUGH THE MID/UPPER  
TROUGH ENTERS THE NORTHEAST CARIBBEAN...THE FORECAST AREA IS TO  
REMAIN ON THE CONVERGENT SIDE OF THIS FEATURE. THIS WILL COMBINE  
WITH BUILDING MID LEVEL RIDGE OVER THE EASTERN CARIBBEAN TO  
GENERALLY FAVOR AN UPPER CONVERGENT/ SUBSIDENT PATTERN THAT IS TO  
STRENGTHEN THE TRADE WINDS CAP DURING THE WEEKEND-EARLY NEXT WEEK.  
IN THIS PATTERN DIURNAL CONVECTION IS TO GENERALLY CONFINE TO  
INTERIOR PORTIONS OF PUERTO RICO IN AFTERNOON CONVECTION.  
ELSEWHERE ELSE...FAIR WEATHER CONDITIONS ARE EXPECTED.  
 
DAVISON...WPC (USA)  
 

 
 
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