Prognostic Meteorological Discussion
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FXCA20 KWBC 261036
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
636 AM EDT THU APR 26 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR 26/06
UTC: CONSISTENT WITH PREVIOUS FORECASTS...SUCCESSIVE MID/UPPER
LEVEL PERTURBATIONS ARE TO HELP SUSTAIN A BROAD TROUGH ACROSS THE
EASTERN USA DURING THE NEXT FEW DAYS. UNDER INFLUENCE OF THIS
FEATURE...A RIDGE IS TO GRADUALLY BUILD NORTH ACROSS THE EASTERN
CARIBBEAN INTO THE ATLANTIC BETWEEN 60W-70W. THE BUILDING RIDGE IS
TO STRENGTHEN THE TRADE WINDS CAP...WITH INVERSION DROPPING TO
800/850 HPA ON FRIDAY. THIS WILL BE ACCOMPANIED BY A SHARP DROP IN
AVAILABLE WATER...AND AS A STRONG TRADE WINDS CAP HOLDS A PWAT
MINIMA IS TO PERSIST ACROSS THE FORECAST AREA THROUGH EARLY NEXT
WEEK.

AT LOW LEVELS...BROAD TROUGH EXTENDS ACROSS THE EASTERN USA TO THE
WESTERN ATLANTIC...A REFLECTION OF THE MID/UPPER LEVEL FEATURE.
UNDER INFLUENCE OF THIS TROUGH...AND A RIDGE TO THE EAST...A DEEP
LAYER SOUTHEASTERLY FLOW ENVELOPS THE EASTERN CARIBBEAN. THIS IS
ADVECTING A DEEP PLUME OF TROPICAL MOISTURE ACROSS THE VIRGIN
ISLES THAT IS TO ADVECT ACROSS PUERTO RICO DURING THE DAY. DEEP
MOISTURE IS TO PERSIST THROUGH THE EARLY MORNING HOURS ON
FRIDAY...WITH MODELS THEN AGREEING ON DRYER AIR ENTRAINING FROM
THE EAST. MEANWHILE...MOIST INFLOW THIS MORNING IS TO FEED
CONVECTIVE DEVELOPMENT DURING THE DAY TODAY. ACROSS THE VIRGIN
ISLES INTO EASTERN PUERTO RICO THIS IS TO GENERALLY FAVOR LIGHT
RAINFALL AMOUNTS. MOST ACTIVE IS TO CLUSTER ACROSS NORTHERN PUERTO
RICO BETWEEN AGUADILLA AND BARCELONETA/VEGA ALTA IN LATE MORNING
AND AFTERNOON CONVECTION. DURING THE FIRST TWO PERIODS EXPECTING
LOCALIZED MAXIMA OF 1-2 INCHES...WITH SOUTHWESTERLY STEERING FLOW
ENHANCING DEVELOPMENT ACROSS THE GUAJATACA BASIN. ON
FRIDAY-SATURDAY...AS THE TRADE WINDS CAP STRENGTHENS...EXPECTING
BELOW NORMAL RAINFALL AMOUNTS ACROSS THE ENTIRE FORECAST AREA.
SEASONAL SHOWERS ARE LIKELY TO RETURN ON SUNDAY-MONDAY AS THE
TRADE WINDS CAP LIFTS ABOVE 750 HPA.

DAVISON...WPC (USA)

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