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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1126Z Apr 08, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
726 AM EDT WED APR 08 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM APR 08/11
UTC: MID/UPPER LEVEL TROUGH CONTINUES TO DOMINATE THE FLOW OVER
THE WESTERN ATLANTIC...WITH AXIS SUSTAINING A SURFACE FRONT THAT
STRETCHES FROM THE CENTRAL ATLANTIC TO JUST NORTH OF THE FORECAST
AREA. MOISTURE IS POOLING ALONG THIS BOUNDARY...WITH PWAT CONTENT
OVER THE FORECAST AREA RANGING BETWEEN 1.25-1.75 INCHES.

AS THE MID/UPPER LEVEL TROUGH HOLDS OVER THE WESTERN ATLANTIC...A
MID LEVEL CYCLONIC VORTEX ROUNDING THE BASE OF THE TROUGH REACHES
THE FORECAST AREA THIS AFTERNOON...MAKING LANDFALL DURING MAX
HEATING. AS IT INTERACTS WITH THE SURFACE FRONT AND MOISTURE
POOLING OVER THE FORECAST AREA...HIGHER RESOLUTION MODEL GUIDANCE
ARE SHOWING HEAVY CONVECTION CLUSTERING OVER INTERIOR PORTIONS OF
PUERTO RICO THIS AFTERNOON...WITH THE ARW AND NMM VERSIONS OF THE
HRWRF SHOWING LOCALIZED MAXIMA OF 2-3 INCHES. ALTHOUGH AS OF LATE
THESE MODELS HAVE BEEN SHOWING A WET BIAS OVER THE
ISLAND...CONSIDERING THAT THE MID LEVEL PERTURBATION MAKES
LANDFALL DURING MAXIMUM HEATING AND WEAK SOUTHWESTERLY VERTICAL
WIND SHEAR...THIS MIGHT BE AN INSTANCE WHERE THE GUIDANCE MIGHT BE
CORRECT. ALTHOUGH NOT AS INTENSE AS THE HRWRF...THE GFS HAS BEEN
CONSISTENT IN SHOWING AN INCREASE IN ACTIVITY DURING THE DAY
TODAY...WHILE THE UKMET AND ECMWF SETTLE ON LESSER AMOUNTS. SO WE
ARE LEANING IN FAVOR OF THE WETTER HIGHER RESOLUTION MODELS.
HOWEVER...IN ADDITION TO A MAXIMA OVER WESTERN INTERIOR PORTIONS
OF PUERTO RICO...IN A MID LEVEL WEST-SOUTHWEST FLOW...EXPECTING A
SECONDARY MAXIMA TO AFFECT PORTIONS OF THE SAN JUAN METRO AREA
THIS AFTERNOON. THIS WILL REQUIRE FOR THE CONVECTIVE CORE TO LIFT
ABOVE 800 HPA...WHICH SEEMS LIKELY DUE TO THE MID LEVEL FORCING.

PATTERN ON THURSDAY UNRAVELS...WITH POLAR TROUGH MEANDERING AWAY
AS A MID LEVEL RIDGE BUILDS FROM THE WEST ACROSS THE GREATER
ANTILLES. AS THE RIDGE SETTLES OVER THE FORECAST AREA...THIS WILL
BE ACCOMPANIED BY RAPID INTENSIFICATION OF THE TRADE WINDS CAP
THROUGH FRIDAY. THE STRONGER CAP WILL BE ACCOMPANIED BY A SHARP
DROP IN PWAT CONTENT DURING THE LATTER PART OF THE WEEK. AT LOW
LEVELS...IN A SOUTH-SOUTHEASTERLY FLOW...THE SURFACE FRONT IS TO
WEAKEN AS IT MEANDERS NORTH ON THURSDAY-FRIDAY. LIGHT AND VARIABLE
WINDS ARE TO THEN SETTLE ACROSS THE FORECAST AREA ON
FRIDAY-SATURDAY. AS THIS COINCIDES WITH STRENGTHENING MID LEVEL
RIDGE...THE GLOBAL MODELS GENERALLY AGREE ON FAIR WEATHER
CONDITIONS TO THEN PREVAIL ACROSS THE FORECAST AREA. DIURNAL
CONVECTION...IF ANY...WILL GENERALLY LIMIT TO HIGHER TERRAIN OVER
THE ISLANDS AND WESTERN INTERIOR PORTIONS OF PUERTO RICO.

DURING MEDIUM RANGE PERIOD...MID/UPPER LEVEL RIDGE TENDS TO
STRENGTHEN ITS FOOTHOLD OVER THE FORECAST AREA...WHILE AT LOW
LEVELS THE WINDS ARE TO BACK TO THE NORTHEAST AS A HIGH/RIDGE
ROLLS ACROSS THE WESTERN ATLANTIC. THIS WILL THEN FAVOR A COOL
ADVECTIVE PATTERN...WITH A HIGHER INCIDENCE OF TRADE WIND SHOWERS
TO PESTER THE VIRGIN ISLES-EASTERN/NORTHERN PUERTO RICO ON SUNDAY
MORNING. THESE ARE TO SUSTAIN LIGHT RAINFALL AMOUNTS IN PASSING
SHOWERS...WITH MEASURABLE AMOUNTS LIMITING TO NORTHEAST AND
INTERIOR PORTIONS OF PUERTO RICO IN AFTERNOON CONVECTION. 

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