Prognostic Meteorological Discussion
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FXCA20 KWBC 231046
PMDCA

TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
645 AM EDT THU MAR 23 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM MARCH
23/06 UTC: AMPLIFYING POLAR TROUGH DOMINATES THE FLOW OVER THE
WESTERN ATLANTIC. AS IT DEEPENS...THE LONG WAVE TROUGH IS PHASING
WITH A SHORT WAVE PERTURBATION TO THE SOUTH. AS THEY MERGE...IT IS
TO EVOLVE INTO A HIGH AMPLITUDE LONG WAVE TROUGH THAT IS TO SPAN
FROM THE WESTERN ATLANTIC TO THE CENTRAL/WESTERN CARIBBEAN. THE
AMPLIFYING TROUGH IS PRESSING AGAINST THE SUBTROPICAL RIDGE TO THE
EAST... TIGHTENING THE GRADIENT WHILE FAVORING INTENSIFICATION OF
A SUBTROPICAL JET MAXIMA ROUNDING THE BASE OF THE TROUGH. THE JET
EXTENDS FROM NICARAGUA/COSTA RICA... CROSSING PUERTO RICO/VIRGIN
ISLES TO THE ATLANTIC. AT LOW LEVELS...BROAD RIDGE OVER THE
EASTERN USA IS DRIVING A POLAR FRONT SOUTH ACROSS THE WESTERN
ATLANTIC TO NORTHERN FLORIDA. BOUNDARY IS TO MOVE TO THE NORTHWEST
BAHAMAS LATER THIS MORNING. UNDER INFLUENCE OF THIS FEATURE AN
INDUCED/PREFRONTAL TROUGH NOW EXTENDS ACROSS THE CENTRAL
CARIBBEAN. THIS COMBINES WITH A BROAD RIDGE EAST OF THE ISLANDS TO
SUSTAIN A MOIST SOUTHEASTERLY FLOW ACROSS THE ISLAND CHAIN TO THE
EASTERN CARIBBEAN...WITH DEEPER MOISTURE GRADUALLY POOLING ACROSS
PUERTO RICO/VIRGIN ISLES.

THE POLAR TROUGH REACHES MAXIMUM AMPLITUDE LATER TODAY. THROUGH
FRIDAY EVENING THIS EVOLVES INTO A BROAD TROUGH THAT IS TO ANCHOR
ON A MEANDERING LOW OVER THE BAHAMAS. AXIS IS TO SLOWLY WEAKEN
DURING THE WEAKEN WHILE SHEARING SHORT WAVE ENERGY ACROSS
HISPANIOLA/MONA PASSAGE-NORTHWEST PORTIONS OF PUERTO RICO. AT 250
HPA THE JET MAXIMA REPOSITIONS JUST NORTH OF PUERTO RICO ON
FRIDAY. ALTHOUGH THE JET TENDS TO WEAKEN...AN UPPER LEVEL
DIVERGENT PATTERN IS EXPECTED TO PERSIST THROUGHOUT THE
WEEKEND/EARLY NEXT WEEK. THIS IS TO VENT CONVECTIVE DEVELOPMENT
DURING THE NEXT FEW DAYS. AT LOW LEVELS THE ASSOCIATED SURFACE
FRONT BOTTOMS OUT ALONG 22N/23N BY MIDDAY ON FRIDAY. THE
INDUCED/PREFRONTAL TROUGH IS TO THEN MEANDER ACROSS THE DOMINICAN
REPUBLIC...MEANWHILE SUSTAINING A MOIST SOUTHEASTERLY FLOW ACROSS
THE FORECAST AREA. DURING THE WEEKEND...UNDER THE INFLUENCE OF THE
MID LEVEL CYCLONE... THIS IS TO EVOLVE INTO A CLOSED LOW ALONG THE
FRONT JUST NORTH OF HISPANIOLA/EAST OF THE TURKS AND CAICOS.

THE GLOBAL MODELS THEN AGREE ON MOST ACTIVE CONVECTION TO DEVELOP
NORTH OF THE ISLANDS ALONG THE MEANDERING SURFACE FRONT AND
NASCENT LOW LEVEL CIRCULATION. THIS IS TO GRADUALLY BECOME MORE
ACTIVE/BETTER ORGANIZED DURING THE WEEKEND. AS ACTIVITY TO THE
NORTH INTENSIFIES...EXPECTING CONVECTION ACROSS PUERTO RICO AND
THE VIRGIN ISLES TO WANE. THUS...WE EXPECT MOST ACTIVE CONVECTION
ACROSS THE FORECAST AREA DURING THE NEXT COUPLE OF DAYS. THE
HIGHER RESOLUTION MODEL GUIDANCE SHOW PEAK IN ACTIVITY ON FRIDAY
AS ENHANCED BY UPPER LEVEL JET MAXIMA...WITH WIDESPREAD MAXIMA OF
3-5 INCHES ACROSS MOST OF PUERTO RICO AND 1-2 INCHES OVER/NEAR THE
VIRGIN ISLES. THIS SEEMS REASONABLE CONSIDERING EVOLVING PATTERN
AND ASSOCIATED MESO-SYNOPTIC FORCING.

JIMENEZ...IMN (COSTA RICA)
SUBRATH-ALI...TTMS (TRINIDAD AND TOBAGO)
DAVISON/GALVEZ...WPC (USA)

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