TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
656 AM EDT TUE MAY 21 2013

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI. PROGRESSIVE
SHORT WAVE TROUGH ON THE SOUTHERN STREAM MOVED ACROSS THE
NORTHEAST CARIBBEAN ISLES AS ANOTHER ENTERS THE BAHAMAS/CUBA.
UNDER INFLUENCE OF THESE PERTURBATIONS...AND A MOIST EASTERLY LOW
LEVEL FLOW...MOISTURE HAS BEGUN TO POOL ACROSS THE CARIBBEAN
WATERS OF PUERTO RICO TO SAINT CROIX.

AT UPPER LEVELS THE MODEL GUIDANCE SHOWS LOW AMPLITUDE TROUGH
ENVELOPING THE NORTHERN CARIBBEAN ISLES OVER THE NEXT FEW
DAYS...WHILE AT MID LEVELS A DISORGANIZED MEANDERING FLOW IS TO
PREVAIL. LOW LEVEL FLOW PATTERN...IN-CONTRAST...APPEARS BETTER
ORGANIZED...AS A BROAD CELL OF THE SUBTROPICAL RIDGE IS TO
DOMINATE THE WESTERN ATLANTIC-CARIBBEAN BASIN. UNDER INFLUENCE OF
THIS RIDGE...A MOIST EAST-SOUTHEAST FLOW IS TO PREVAIL THROUGH THE
END OF THE WEEK. MODEL GUIDANCE CONTINUES TO SHOW MOISTURE SURGING
AND POOLING ON THE CARIBBEAN WATERS OF PUERTO RICO INTO THE
SOUTHERN VI. THE ECMWF NOW JOINS THE GFS IN SHOWING PWAT OF NEARLY
TWO INCHES BY LATER THIS EVENING/EARLY ON WEDNESDAY...TO THEN
PERSIST FOR FEW DAYS. THIS WILL BE ENOUGH TO FUEL ORGANIZED
CONVECTION ACROSS THE FORECAST AREA.

EVOLVING MESO-SYNOPTIC FLOW PATTERN AND FAVORABLE MJO CONDITIONS
TRANSLATE TO AN ACTIVE WEATHER REGIME ACROSS THE FORECAST AREA
DURING THE NEXT FEW DAYS. THE GFS REMAINS THE MOST AGGRESSIVE WITH
ITS RAINFALL AMOUNTS...SHOWING DAILY MAXIMA IN EXCESS OF 2
INCHES...WHILE THE EUROPEAN MODELS GENERALLY PEAK AT 1 INCH. IN A
WEAK STEERING FLOW...HIGH RESOLUTION MODELS HAVING HARD TIME WITH
THIS REGIME...BUT THEY GENERALLY WANT TO HIGHLIGHT POTENTIAL FOR
MODERATE TO HEAVY SHOWERS ACROSS EASTERN PORTIONS OF PUERTO RICO.
MOST LIKELY WE ARE TO SEE WIDESPREAD CONVECTION ACROSS FORECAST
AREA...AND IN A LIGHT EASTERLY FLOW THE MOST INTENSE IS TO CLUSTER
OVER EL YUNQUE IN THE LATE MORNING/EARLY AFTERNOON HOURS AND
WESTERN PORTIONS OF PUERTO RICO IN THE AFTERNOON. DURING THE
PERIOD...DAILY MAXIMA COULD EASILY PEAK AT 2-3 INCHES. HEAVY RAINS
ARE ALSO LIKELY ACROSS SAINT CROIX OVER THE NEXT COUPLE OF
DAYS...WITH LIGHT TO MODERATE TO AFFECT SAINT JOHN AND SAINT
THOMAS.

BLENMAN...BMS (BARBADOS)
MCKENZIE...BDM (BAHAMAS)
DAVISON/GALVEZ...WPC (USA)