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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1220Z Feb 12, 2018)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
720 AM EST MON FEB 12 2018

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM FEB 12/06
UTC: A ROBUST MID-UPPER TROUGH LIES OVER THE TROPICAL ATLANTIC.
THE TROUGH HAS A BROAD AXIS THAT EXTENDS INTO THE CARIBBEAN ACROSS
20N 50W...THE LEEWARD ISLANDS AT 17N 62W...INTO SOUTHERN PUERTO
RICO. THIS UPPER TROUGH IS DESTABILIZING THE BOUNDARY LAYER BY
WEAKENING THE TRADE WIND CAP. THIS IS ALLOWING THE VERTICAL
DEVELOPMENT OF ATLANTIC TRADE WIND SHOWERS TO 700 HPA. ONE OF THE
LIMITATIONS FOR THE DEVELOPMENT OF HEAVY RAIN IS THE LIMITED
AVAILABILITY OF MOISTURE ABOVE THE BOUNDARY LAYER. THE SECOND
LIMITATION IS THE SPEED OF THE TRADES. AS 30-35KT TRADES REMAIN AT
850-925 HPA...AND OVER 20KT JUST ABOVE 1000 HPA...EXPECTING THE
SHOWERS TO CONTINUE STREAMING TO THE WEST-SOUTHWEST.

MODELS FORECAST THE UPPER TROUGH TO PERSIST WHILE RESTRUCTURING
THROUGH THE CYCLE. THIS WILL CONTINUE SUSTAINING A DESTABILIZATION
OF THE ATLANTIC BOUNDARY LAYER...AND ALLOWING THE DEVELOPMENT OF
WEAK TROUGH IN THE TRADES ALONG WHICH ENHANCED MOISTURE WILL
ORGANIZE. THESE RAPIDLY PASSING PERTURBATIONS WILL MODULATE THE
VARIABILITY OF PRECIPITATION IN THE ISLANDS DURING THE COMING
DAYS. TRADE WINDS ARE FORECAST TO REMAIN ACCELERATED THROUGH EARLY
WEDNESDAY...TO THEN DECREASE TO SPEEDS OF 15-25KT AT 925-850 HPA
AND LOWER SPEEDS NEAR THE SURFACE. MODELS SHOW THAT A SLIGHT
NORTHEASTERLY COMPONENT WILL PREVAIL THROUGHOUT THE WEEK. THIS
PATTERN IS FAVORABLE FOR BRIEF PASSING SHOWERS PESTERING THE
NORTHERN COAST OF PUERTO RICO ESPECIALLY DURING THE MORNING. SOME
ENHANCEMENT OF RAINFALL RATES WILL BE PROVIDED BY THE UPPER
TROUGH...YET EXPECTING ACTIVITY TO BE BRIEF.

IN TERMS OF ACCUMULATIONS...LARGEST AMOUNTS ARE EXPECTED IN
NORTHEASTERN PUERTO RICO WHERE ENHANCED MOISTURE CONVERGENCE WILL
FAVOR DAILY ACCUMULATIONS OF 0.5-1 INCHES. ALONG THE NORTHERN
COAST OF PUERTO RICO...EXPECTING ACCUMULATIONS OF 0.25-0.5
INCHES/DAY ESPECIALLY ON MONDAY AND TUESDAY.

GORDON...NMS (BELIZE)
NIXON...BDM (THE BAHAMAS)
GALVEZ...WPC (USA)