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Tropical Discussion
 
(Latest Discussion - Issued 1146Z Nov 27, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
646 AM EST FRI NOV 27 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM NOV
27/12UTC: A MID LEVEL HIGH OVER THE YUCATAN/CAMPECHE SOUND EXTENDS
A RIDGE EAST EAST ACROSS THE NORTHERN CARIBBEAN...WITH AXIS
FAVORING A MID LEVEL CAP INVERSION ACROSS THE NORTHEAST CARIBBEAN
ISLANDS. EAST OF THIS AXIS...A CLOSED LOW NEAR 27 58W EXTENDS A
TROUGH SOUTH TO THE EAST OF THE ISLAND CHAIN TO JUST NORTH OF THE
GUIANAS. AT LOW LEVELS...THE LATTER REFLECTS AS A CLOSED LOW TO
THE NORTH-NORTHEAST OF THE LEEWARDS. THIS COMBINES WITH A RIDGE TO
THE WEST TO FAVOR A FRESH NORTHEASTERLY FLOW. EMBEDDED IN THIS
FLOW...SATELLITE IMAGERY SHOWS A SHALLOW PLUME OF MOISTURE
EXTENDING EAST-TO-WEST JUST NORTH OF 20N. DRIVEN BY THE
NORTHEASTERLY WINDS...THIS IS EXPECTED TO MEANDER SOUTH...REACHING
THE FORECAST AREA EARLY ON SATURDAY MORNING. MEANWHILE...THE
NORTHEASTERLY TRADES ARE TO CONTINUE FOCUSING THE BULK OF THE
DIURNAL CONVECTION ACROSS THE CORDILLERA IN PUERTO RICO...WHERE IN
AN ELEVATED CAP CONDITIONS REMAIN FAVORABLE FOR MODERATE RAINFALL
AMOUNTS. BUT CONSISTENT WITH PREVIOUS FORECASTS...THIS IS EXPECTED
TO GRADUALLY WEAKEN OVER THE NEXT COUPLE OF DAYS. NOCTURNAL
ACTIVITY...HOWEVER...IS TO SEE AN INCREASE EARLY ON SATURDAY AS
SHALLOW PLUME PROPAGATES ACROSS THE NORTHERN VI INTO PUERTO RICO.
BUT THIS IS TO ONLY TRIGGER LIGHT RAINFALL AMOUNTS ACROSS THE
ATLANTIC WATERS INTO NORTHERN PUERTO RICO AND THE NORTHERN VI
THROUGH DAYBREAK ON SATURDAY.

THROUGH THE WEEKEND MID/UPPER PATTERN IS TO RAPIDLY EVOLVE...WITH
RIDGE ENVELOPING THE NORTHERN CARIBBEAN TO RAPIDLY ERODE AS POLAR
TROUGH AMPLIFIES ACROSS THE USA INTO THE GULF OF MEXICO. IN
RESPONSE...CLOSED HIGH RELOCATES ACROSS THE NORTHERN CARIBBEAN TO
THE DOMINICAN REPUBLIC...WHERE IT IS TO THEN HOLD THROUGHOUT THE
MEDIUM RANGE PERIOD. UNDER THE INFLUENCE OF THIS FEATURE...THE
GLOBAL AND REGIONAL MODELS AGREE ON RAPID INTENSIFICATION OF THE
TRADE WINDS INVERSION...WITH CAP SETTLING AROUND 800-850 HPA. AT
LOW LEVELS...GRADIENT SLACKENS AND THE TRADES ARE TO WEAKEN...WITH
LIGHT EAST-NORTHEASTERLY FLOW TO DOMINATE THE BOUNDARY LAYER WHILE
AT 850 HPA AND ABOVE LIGHT/MEANDERING WINDS ARE TO PREVAIL. THIS
PATTERN WILL THEN BECOME HOSTILE TO CONVECTIVE DEVELOPMENT DURING
THE WEEKEND...WITH FAIR WEATHER CONDITIONS EXPECTED TO PREVAIL
THROUGH THE MIDDLE OF NEXT WEEK.

DAVISON...WPC (USA)