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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1053Z Sep 19, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
653 AM EDT WED SEP 19 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM SEP 19/06
UTC: A MID-LEVEL RIDGE CENTERS AT 24N AND 55W AND EXTENDS AN AXIS
INTO PUERTO RICO AND THE DOMINICAN REPUBLIC. THE RIDGE IS BUILDING
ACROSS THE EASTERN CARIBBEAN. A TROPICAL WAVE IS ENTERING THE
BASIN AND EXTENDS ALONG 61W...YET THE MOIST PLUME ASSOCIATED WITH
THE WAVE LIES TO THE SOUTH OF 15N...AND SCATTERED CONVECTION
EXTENDS FROM THE FRENCH ANTILLES TO THE SOUTH. THIS PERTURBATION
IS BEING TRAILED BY A STRONG SAHARAN AIR LAYER (SAL). THE FRONTAL
EDGE OF THE SAL EXTENDS ALONG 60W...JUST TO THE EAST OF THE
LEEWARD ISLANDS.

MODELS CONTINUE SUGGESTING THE MID-LEVEL RIDGE BUILDING INTO THE
NORTHEASTERN CARIBBEAN AND LIMITING THE NORTHWARD INCURSION OF
TROPICAL MOISTURE ASSOCIATED WITH THE TROPICAL WAVE. UNDER FAST
15-20KT EAST-SOUTHEASTERLY ESTABLISHING TODAY AND LASTING THROUGH
EARLY FRIDAY...EXPECTING RAINFALL ACCUMULATIONS TO CLUSTER IN THE
VIRGIN ISLANDS AND SOUTHEASTERN PUERTO RICO IN MORNING HOURS...AND
EXTREME WESTERN AND NORTHWESTERN PUERTO RICO IN THE AFTERNOON. DUE
TO ENHANCED SHEAR AND RAPID PROPAGATION OF CONVECTION...EXPECTING
MAXIMA TO REMAIN NEAR OR UNDER 1 INCH IN EXTREME NORTHWESTERN
PUERTO RICO. THE CURRENT PATTERN WILL FAVOR THE DEVELOPMENT OF
STREAMERS THAT WILL ENHANCE PRECIPITATION LOCALLY IN EASTERN
PUERTO RICO/VI...AND IN AREAS NEAR OR JUST TO THE SOUTH OF THE SAN
JUAN METRO DURING THE DAY...TO PRODUCE MAXIMA IN THE ORDER OF
0.3-0.5 INCHES.

THE SAL ARRIVES ON THURSDAY EVENING. THIS WILL ARRIVE WITH A
STRONG TRADE WIND INVERSION AT 900 HPA AND ASSOCIATED FAIR WEATHER
CONDITIONS ON FRIDAY. TRADE WINDS ARE FORECAST TO BECOME
EAST-NORTH EASTERLIES AND DECREASE IN SPEED TO 05-10KT...WHICH
WILL FAVOR AFTERNOON CONVECTION IN WESTERN/SOUTHWESTERN PUERTO
RICO TO PRODUCE MAXIMA UNDER 0.5 INCHES. THIS WIND PATTERN WILL
ALSO FAVOR LIGHT RAIN SHOWERS ALONG NORTHERN AND EASTERN PUERTO
RICO ON FRIDAY EVENING INTO EARLY SATURDAY.

WARD-FORBES...BDM (THE BAHAMAS)
TEJADA...AAC (PANAMA)
GALVEZ...WPC (USA)