195  
FXCA20 KWBC 011136  
PMDCA  
 
TROPICAL DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
636 AM EST THU FEB 01 2018  
 
PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 01/06  
UTC: FORECAST AREA REMAINS ON THE CONVERGENT SIDE OF A MID LEVEL  
RIDGE THAT EXTENDS FROM THE WESTERN CARIBBEAN/YUCATAN PENINSULA TO  
THE NORTHERN CARIBBEAN ISLES. THIS IS BLOCKING A POLAR TROUGH FAR  
TO THE NORTH...WITH ASSOCIATED FRONTAL BOUNDARY BOTTOMING OUT  
NORTH OF THE FORECAST AREA. BROAD POLAR RIDGE TO THE NORTH FAVORS  
A COOL ADVECTIVE PATTERN ACROSS THE NORTHEAST CARIBBEAN ISLES.  
THIS...IN-TURN...TRIGGERED SHALLOW CONVECTIVE INSTABILITY AND  
GENERATION OF A CLOUD CLUSTER THAT IS STREAMING ACROSS THE  
NORTHERN LEEWARD/VIRGIN ISLES TO PUERTO RICO. BUT AS IT SLIDES  
UNDER A STRONG LOW LEVEL CAP INVERSION...AND LACKING VERTICAL  
DEVELOPMENT...THIS IS TO ONLY FAVOR LIGHT RAINFALL AMOUNTS AS IT  
STREAMS ACROSS THE FORECAST AREA EARLY THIS MORNING. WARMING  
DURING THE DAY WILL HELP DISSIPATE THIS CLUSTER...LEADING TO FAIR  
WEATHER CONDITIONS DURING THE AFTERNOON HOURS.  
 
MODELS AGREE ON PERSISTENT MID LEVEL RIDGE PATTERN TO MAINTAIN ITS  
FOOTHOLD ACROSS THE NORTHERN CARIBBEAN THROUGH THE LONG RANGE  
PERIOD...WITH ASSOCIATED TRADE WINDS CAP TO CONTINUE INHIBITING  
ORGANIZED DEEP CONVECTION. POLAR TROUGHS EXITING THE EASTERN USA  
ARE TO THEN LIFT OVER THIS RIDGE...IN A VERY SEASONAL PATTERN FOR  
THIS TIME OF THE YEAR. AT LOW LEVELS...LACKING STRONG UPPER LEVEL  
SUPPORT...POLAR FRONTS STREAMING ACROSS THE WESTERN ATLANTIC ARE  
TO BOTTOM OUT FAR TO THE NORTH OF THE FORECAST AREA. LOCAL FLOW  
WILL THEN DEPEND ON TRANSITORY POLAR RIDGES ROLLING ACROSS THE  
WESTERN-CENTRAL ATLANTIC FROM TIME-TO-TIME. THESE ARE TO FAVOR  
PERIODS OF BRISK NORTHEASTERLY TRADES...WITH BOUNDARY LAYER WINDS  
EXPECTED TO PEAK BETWEEN 15-20KT. THE FRESH NORTHEASTERLY TRADES  
WILL SUSTAIN A COOL ADVECTIVE PATTERN...AND ARE TO CONTINUE  
FAVORING GENERATION OF CLOUD CLUSTERS THAT ARE TO STREAM ACROSS  
THE FORECAST AREA. THIS IS TO ALSO FAVOR GENERATION OF STREAMERS  
DURING THE DAYTIME HOURS TO AFFECT THE VIRGIN ISLES AND EASTERN  
PORTIONS OF PUERTO RICO. ON FRIDAY-SATURDAY THE LOW LEVEL FLOW  
GROWS SOMEWHAT MORE PERTURBED...WITH GFS CONSISTENTLY SHOWING AN  
INCREASE OF LOW LEVEL FORCING OVER THE FORECAST AREA. BOTH THE GFS  
AND ECMWF THEN SHOW PWAT CONTENT OF 1.0 TO 1.25 INCHES ON  
FRIDAY-SATURDAY...TO FEED CONVECTIVE DEVELOPMENT DURING THE DAY.  
ON SUNDAY A DRYER AIR MASS ENTRAINS FROM THE EAST...BUT THIS WILL  
BE SHORT LIVED. SHALLOW MOISTURE IS TO ONCE AGAIN ADVECT ACROSS  
THE FORECAST AREA EARLY NEXT WEEK.  
 
GORDON...NMS (BELIZE)  
NIXON... (THE BAHAMAS)  
DAVISON/GALVEZ...WPC (USA)  
 

 
 
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