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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1149Z Dec 12, 2017)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
649 AM EST TUE DEC 12 2017

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM DEC 12/06
UTC: BROAD POLAR TROUGH EXTENDS FROM THE CENTRAL USA TO THE
WESTERN ATLANTIC...WITH AXIS BOTTOMING OUT NORTH OF 20N. ALSO AT
MID LEVELS...A LOW AMPLITUDE RIDGE EXTENDS WEST-TO-EAST ACROSS THE
CARIBBEAN BASIN...FAVORING A FAIRLY STRONG TRADE WINDS CAP ACROSS
THE EASTERN CARIBBEAN ISLES. AT LOW LEVELS...THE TROUGH ALOFT
SUSTAINS A SURFACE FRONT THAT STRETCHES ACROSS THE BAHAMAS-CUBA TO
THE WESTERN CARIBBEAN. OVER THE EASTERN CARIBBEAN...IN RESPONSE TO
THIS FEATURE...A LIGHT MEANDERING FLOW DOMINATES.

GLOBAL MODELS FORECAST A CLIPPER TO STREAM ACROSS THE EASTERN USA
LATER THIS AFTERNOON. AS IT ROUNDS THE BASE OF THE LONG WAVE
TROUGH NORTH OF THE ISLANDS...IT IS TO PRESS AGAINST THE MID LEVEL
RIDGE TO THE SOUTH. UNDER PRESSURE...THE RIDGE IS TO RELAX ITS
FOOTHOLD ACROSS THE EASTERN CARIBBEAN...WITH STRONG TRADE WINDS
CAP LIFTING ABOVE 700 HPA BY MIDDAY ON WEDNESDAY. DURING THAT
PERIOD THE PWAT CONTENT IS TO PEAK AROUND 1.25 INCHES. THE
SLIGHTLY MORE FAVORABLE ENVIRONMENTAL CONDITIONS...HOWEVER...WILL
BE SHORT LIVED. ON THURSDAY-FRIDAY MID LEVEL RIDGE PATTERN BOUNCES
BACK...STRENGTHENING THE TRADE WINDS CAP ACROSS THE CARIBBEAN
WHILE SUSTAINING A DRYING TREND. AT LOW LEVELS...THE POLAR FRONT
SLOWLY MOVES ACROSS THE TURKS AND CAICOS TO NORTHERN HISPANIOLA ON
WEDNESDAY MORNING. BUT AS IT LOSES ITS UPPER LEVEL
SUPPORT...FRONTAL BOUNDARY IS TO THEN GRADUALLY WEAKEN WHILE
RETROGRESSING ACROSS THE BAHAMAS-CUBA LATER IN THE WEEK. EVOLVING
LOW/MID LEVEL PATTERN TO THE WEST AND NORTH WILL HAVE AN INFLUENCE
ON THE LOCAL FLOW PATTERN. EARLY THIS MORNING THE STEERING FLOW
BECOME SLIGHTLY BETTER DEFINED AS THE WINDS  VEER TO THE
SOUTH-SOUTHEAST...SHIFTING TO THE SOUTH-SOUTHWEST LATER IN THE
DAY/EARLY WEDNESDAY MORNING. ON THURSDAY-FRIDAY...AS A RIDGE
GRADUALLY BUILDS TO THE NORTH...THE PREVAILING EASTERLY TRADES
RETURN TO THE FORECAST AREA. STRONGER WINDS ARE EXPECTED BY THE
END OF THE WEEK.

AS THE WINDS VEER TO THE SOUTH...EXPECTING SLIGHT INCREASE IN
DIURNAL CONVECTION ALONG THE CORDILLERA-NORTHERN PUERTO RICO
DURING THE DAY TODAY. SLIGHTLY HIGHER AMOUNTS ARE EXPECTED ON
WEDNESDAY AS THE MID LEVEL RIDGE PATTERN WEAKENS AND DEEPER
MOISTURE POOLS ACROSS THE FORECAST AREA. ON THURSDAY AND ONWARD
EXPECTING A LULL IN ACTIVITY...WITH EARLY MORNING TRADE WIND
SHOWERS OVER THE VIRGIN ISLES-EASTERN PUERTO RICO TO ONLY TRIGGER
LIGHT RAINFALL AMOUNTS. LIKEWISE ACROSS WESTERN INTERIOR PORTIONS
OF PUERTO RICO IN AFTERNOON CONVECTION.

GORDON...NMS (BELIZE)
PECK...MS (JAMAICA)
RIVAS...SENAMHI (PERU)
GALVEZ/DAVISON...WPC (USA)