Prognostic Meteorological Discussion
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FXCA20 KWBC 251041
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
640 AM EDT WED APR 25 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR 25/06
UTC: WEST OVER THE DOMAIN...SUCCESSIVE MID/UPPER LEVEL
PERTURBATIONS WILL PROVIDE SUPPORT TO A DEEPENING TROUGH ACROSS
THE EASTERN USA/WESTERN ATLANTIC. AS THE TROUGH DEEPENS TO THE
WEST...A MID LEVEL RIDGE IS TO THEN BUILD NORTH FROM THE EASTERN
CARIBBEAN INTO THE ATLANTIC. THE RIDGE IS TO GRADUALLY BUILD
THROUGH FRIDAY MORNING...AND IT IS TO THEN HOLD THROUGHOUT THE
WEEKEND. AS THE RIDGE INTENSIFIES...IT IS TO STRENGTHEN THE TRADE
WINDS CAP ACROSS THE NORTHEAST CARIBBEAN ISLES...WITH TRADE WINDS
CAP EXPECTED TO SETTLE AROUND 800 HPA EARLY ON FRIDAY MORNING.
THIS WILL BE ACCOMPANIED BY THE RAPID EROSION OF AVAILABLE WATER.

AT LOW LEVELS...POLAR TROUGH ENTERS THE WESTERN ATLANTIC EARLY IN
THE CYCLE. IN RESPONSE TO THIS FEATURE THE LOW LEVEL WINDS ACROSS
THE EASTERN CARIBBEAN ARE TO VEER TO THE SOUTHEAST LATER TODAY.
THIS IS TO THEN ADVECT A PLUME OF DEEP TROPICAL MOISTURE ACROSS
THE FORECAST AREA...REACHING THE VIRGIN ISLES EARLY ON THURSDAY
MORNING AND MOVING ACROSS PUERTO RICO LATER IN THE DAY. THIS PLUME
WILL SUSTAIN AN INCREASE IN DIURNAL CONVECTION ACROSS THE FORECAST
AREA ON THURSDAY. IN A SOUTHEASTERLY STEERING FLOW MOST ACTIVE IS
FORECAST TO CLUSTER BETWEEN AGUADILLA AND BARCELONETA IN NORTHERN
PUERTO RICO...WHILE LIGHT TO MODERATE CONVECTION BUILDING ALONG
THE CORDILLERA AND EASTERN PORTIONS OF PUERTO RICO. BRISK LOW
LEVEL WINDS ARE TO ALSO FAVOR GENERATION OF STREAMERS ACROSS THE
VIRGIN ISLES...BUT THESE ARE TO RESULT IN LIGHT RAINFALL AMOUNTS
IN PASSING SHOWERS.

PREVAILING EASTERLY TRADES RETURN TO THE FORECAST AREA ON FRIDAY.
THIS WILL BE ACCOMPANIED BY A STRONGER TRADE WINDS CAP AND
ENTRAINMENT OF A DRYER AIR MASS FROM THE EAST. A PWAT MINIMA IS TO
ENVELOP THE ENTIRE FORECAST AREA THROUGH SUNDAY MORNING...TO FAVOR
BELOW NORMAL RAINFALL AMOUNTS IN WIDELY ISOLATED DIURNAL
CONVECTION. LATER ON SUNDAY THE MODELS SHOW A SHALLOW PLUME OF
MOISTURE ADVECTING ACROSS THE FORECAST AREA. THIS IS TO FEED
DIURNAL CONVECTION ACROSS INTERIOR PORTIONS OF PUERTO RICO...BUT
LACKING UPPER LEVEL SUPPORT ONLY EXPECTING LIGHT RAINFALL AMOUNTS.

DAVISON...WPC (USA)

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