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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1207Z Apr 05, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
807 AM EDT SUN APR 05 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR 05/11
UTC: IN A SINUSOIDAL PATTERN...A MID/UPPER LEVEL RIDGE OVER THE
GULF OF MEXICO FAVORS THE SOUTHWARD AMPLIFICATION OF A BROAD
TROUGH OVER THE WESTERN ATLANTIC TO THE NORTHERN CARIBBEAN
ISLANDS. THIS PATTERN IS TO GENERALLY HOLD THROUGH THE END OF THE
WEEK. AS THE PATTERN HOLDS...SHORT WAVE PERTURBATIONS ROUNDING THE
BASE OF THE TROUGH ARE TO STREAM OVER THE FORECAST AREA FROM
TIME-TO-TIME. TIMING THESE PERTURBATIONS IS GOING TO BE ONE OF THE
MANY CHALLENGES WE WILL BE FACING IN THIS FORECAST CYCLE...WITH
MODELS SHOWING A FAIRLY STRONG UPPER LEVEL PERTURBATION ENTERING
THE FORECAST AREA ON THURSDAY.

AT LOW LEVELS...MEANDERING FRONT TRAILS ACROSS THE ATLANTIC TO
JUST NORTH OF THE FORECAST AREA...WITH BOUNDARY LAYER WINDS
MAINTAINING AN EAST-TO-NORTHEAST COMPONENT WHILE AT 850 HPA THEY
STREAM FROM THE WEST-SOUTHWEST. ALTHOUGH LIGHT...THIS IS STRONG
ENOUGH TO FAVOR WEAK VERTICAL SHEAR ACROSS THE FORECAST AREA. THE
FRONT IS FORECAST TO MEANDER BACK AND FORTH OVER THE FORECAST AREA
DURING THE NEXT FEW DAYS. OVER THE LAST FEW DAYS MODELS HAVE BEEN
STRUGGLING WITH MOISTURE CONTENT IN ASSOCIATION WITH THIS
FEATURE...WITH THE ECMWF CONSISTENTLY SHOWING A SHALLOW PLUME OF
MOISTURE WITH CONTENT OF 1.5-1.75 INCHES...WHILE THE GFS WAS
FAVORING LESSER AMOUNTS. ON ITS LATEST COUPLE OF
RUNS...HOWEVER...THE GFS HAS STARTED TO TREND IN FAVOR OF THE
HIGHER MOISTURE CONTENT. THIS IS NOW REFLECTED IN THE DAILY
RAINFALL FORECAST...WITH THE GFS SHOWING AN INCREASE IN DIURNAL
ACTIVITY. OVER THE LAST FEW DAYS THE NMM VERSION OF THE HRWRF HAS
BEEN DOING A GOOD JOB CAPTURING THIS PATTERN AS IT AFFECTS PUERTO
RICO...GIVING SUPPORT TO THE ECMWF...AND NOW THE GFS. SO IN A
HIGHER CONFIDENCE FORECAST...EXPECTING DIURNAL ACTIVITY TO
CONTINUE CLUSTERING ACROSS INTERIOR PORTIONS OF PUERTO RICO...WITH
LOCALIZED MAXIMA OF 1-2 INCHES POSSIBLE...WITH LESSER AMOUNTS
ACROSS THE VIRGIN ISLES-VIEQUES AND CULEBRA. PEAK IN CONVECTION IS
EXPECTED ON THURSDAY AS THE STRONGER MID/UPPER LEVEL VORTEX
STREAMS ACROSS THE FORECAST AREA.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)