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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1159Z Jul 06, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
759 AM EDT MON JUL 06 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JUL 06/12
UTC: MID LEVEL ANALYSIS SHOWS A CLOSED HIGH OVER THE CENTRAL
ATLANTIC EXTENDING A RIDGE TO THE WESTERN ATLANTIC/NORTHERN
CARIBBEAN ISLANDS. AS IT MEANDERS OVER THE GREATER ANTILLES THIS
FAVORS AN ELEVATED INVERSION...STRONG ENOUGH TO INHIBIT ORGANIZED
DEEP CONVECTION BUT NOT STRONG ENOUGH TO SUPPRESS DEVELOPMENT. AT
LOW LEVELS...A TROPICAL WAVE IS STREAMING ACROSS THE EASTERN
CARIBBEAN...WITH AXIS DRAWING A SHALLOW PLUME OF MOISTURE ACROSS
THE ISLAND CHAIN. DURING THE DAY...AS IT STREAMS ACROSS PUERTO
RICO...THIS IS TO FEED A SLIGHT INCREASE IN DIURNAL CONVECTION
ACROSS INTERIOR PORTIONS OF PUERTO RICO...WITH MOST ACTIVE TO
EXPECTED THIS AFTERNOON BETWEEN MAYAGUEZ-ANASCO-LAS MARIAS...WHERE
THE DETERMINISTIC AND ENSEMBLE MODELS AGREE ON POTENTIAL FOR
LOCALLY HEAVY RAINFALL AMOUNTS. OTHERWISE...ONLY EXPECTING LIGHT
RAINFALL AMOUNTS WITH THIS FEATURE OVER THE VIRGIN ISLES-EASTERN
PUERTO RICO.

A STRONGER WAVE FOLLOWS...WITH AXIS REACHING THE ISLAND CHAIN BY
MIDAFTERNOON ON TUESDAY. AS THE PROGRESSIVE WAVE RACES ACROSS THE
EASTERN CARIBBEAN TO THE VIRGIN ISLES LATER IN THE DAY...TRADE
WINDS INVERSION IS EXPECTED TO RELAX ITS FOOTHOLD OVER THE
FORECAST AREA. DURING THIS PERIOD THE GFS AND ECMWF GDI FORECAST
SHOW A HIGHER POTENTIAL RISK FOR THUNDERSTORMS TO DEVELOP...WITH
BEST FORCING EXPECTED ACROSS SAINT CROIX. THROUGH THE EARLY
MORNING HOURS ON WEDNESDAY THE WAVE WILL RACE ACROSS PUERTO
RICO...CROSSING THE MONA PASSAGE INTO THE DOMINICAN REPUBLIC BY
DAYBREAK. ALTHOUGH THE MODELS ARE SHOWING WIDESPREAD CONVECTION AS
THIS WAVE PULLS ACROSS PUERTO RICO...THE STRONGER FORCING WITH
THIS FEATURE APPEARS TO BE ALONG THE SOUTH COAST OF PUERTO RICO
AND CARIBBEAN COASTAL WATERS. THUS LEANING IN FAVOR OF HIGHER
RAINFALL AMOUNTS CLUSTERING BETWEEN THE CORDILLERA AND SOUTH COAST
OF PUERTO RICO. TRAILING PLUME OF MOISTURE WILL FEED A SECOND
ROUND OF DIURNAL CONVECTION ACROSS WESTERN INTERIOR PORTIONS OF
PUERTO RICO DURING THE LATE MORNING-EARLY AFTERNOON HOURS. BUT
THIS IS TO QUICKLY EBB AS A TRAILING DRY AND DUSTY SAHARAN AIR
LAYER ADVECTS ACROSS THE ISLAND CHAIN TO THE FORECAST AREA LATER
IN THE DAY.

THE TRADE WINDS INVERSION IS TO INTENSIFY AS THE SAL SETTLES OVER
THE ISLANDS...LEADING TO MOSTLY FAIR WEATHER CONDITIONS OVER THE
FORECAST AREA ON THURSDAY-FRIDAY MORNING. A GRADUAL INCREASE IN
DIURNAL ACTIVITY IS EXPECTED DURING THE WEEKEND AS THE DUST EBBS
AND PATCHY CLOUD CLUSTERS IN THE EMBEDDED IN THE EASTERLY TRADES
STREAM ACROSS THE NORTHEAST CARIBBEAN. 

DAVISON...WPC (USA)