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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1126Z Sep 17, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
726 AM EDT THU SEP 17 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM SEP
17/11UTC: NHC IS ISSUING ADVISORIES FOR HURRICANE
TEDDY...FORECASTING THE CYCLONE TO INTENSIFY TO A MAJOR HURRICANE
AS IT LIFTS TO THE NORTHWEST.

HURRICANE TEDDY STEERED THE REMNANTS OF RENE ACROSS THE LEEWARD
ISLES EARLY THIS MORNING...AND THROUGH MIDDAY IT IS TO MOVE ACROSS
THE VIRGIN ISLES TO PUERTO RICO. GFS MADE CORRECTIONS TO ITS
FORECAST AND IT NOW ALIGNS BETTER WITH THE FAVORED ECMWF SOLUTION.
UNDER INFLUENCE OF THIS PERTURBATION EXPECTING SCATTERED
CONVECTION AS IT STREAMS ACROSS THE USVI TO PUERTO RICO...TO
SUSTAIN LIGHT TO MODERATE RAINFALL AMOUNTS ACROSS THE VIRGIN
ISLES. OVER PUERTO RICO THE MOST ACTIVE IS TO CLUSTER ACROSS
NORTHEAST PORTIONS OF THE ISLAND/EL YUNQUE RAINFOREST THROUGH
MIDDAY TODAY...WITH A SECONDARY MAXIMA TO THE SOUTHWEST LATER IN
THE AFTERNOON. ACTIVITY TO THE SOUTHWEST MIGHT LINGER INTO THE
EARLY EVENING HOURS.

ALOFT...A DEEPENING TUTT LOW TO THE NORTH...AS IT INTERACTS WITH
HURRICANE TEDDY...IS TO RETROGRESS TOWARDS THE NORTHEAST
CARIBBEAN. THE CLOSED LOW COMES TO A HALT NORTH OF THE ISLANDS
LATER ON FRIDAY...WHILE EXTENDING A SHORT WAVE TROUGH ACROSS
EASTERN HISPANIOLA-PUERTO RICO TO THE NORTHEAST CARIBBEAN. THE
MODELS GENERALLY AGREE ON THIS FEATURE THROUGH SUNDAY MORNING. BUT
AS TEDDY STRENGTHENS TO THE NORTH...THE ECMWF FORECASTS THE UPPER
LOW TO RAPIDLY WEAKEN TO AN OPEN TROUGH ON SUNDAY. THE GFS...IN
CONTRAST...HAS THE LOW REMAINING WELL ORGANIZED THROUGHT THE
WEEKEND TO EARLY NEXT WEEK. THE UKMET IS THE TIE BRAKER...SIDING
WITH THE WEAKER EUROPEAN MODEL. SINCE THE GFS HAS BEEN SO
INCONSISTENT WITH THIS EVOLUTION AND THE UPPER LOW IS TO REMAIN
CUTOFF FROM THE FLOW...OUR CONFIDENCE ON ITS SOLUTION IS LOW. SO
WE ARE LEANING IN FAVOR OF THE WEAKER EUROPEAN MODELS. AT LOW
LEVELS...AS TEDDY LIFTS TO THE NORTHWEST...IT IS TO SUSTAIN A LONG
FETCH NORTHEASTERLY FLOW ACROSS THE FORECAST AREA ON FRIDAY...WITH
WIDELY ISOLATED EARLY MORNING SHOWERS TO AFFECT THE NORTHERN VI
AND NORTH COAST OF PUERTO RICO. DURING THE DAY ON FRIDAY...THE
FOCUS OF THE CONVECTION SHIFTS ALONG THE CORDILLERA/SOUTHWEST
PUERTO RICO...WITH SOME ENHANCEMENT LATER IN THE DAY AS THE UPPER
TROUGH SETTLES NORTH OF THE ISLAND.

IN LIGHT MEANDERING LOW LEVEL FLOW...DIURNAL CONVECTION ACROSS
PUERTO RICO BECOMES MORE WIDESPREAD...WITH A SOUTHWESTERLY UPPER
LEVEL SHEAR TO DRAW THE ACTIVITY TO THE NORTH-NORTHEAST ACROSS
PUERTO RICO TO THE SAN JUAN METRO AREA...WHERE SOME OF THE
ENSEMBLE MEMBERS SHOW POTENTIAL FOR MODERATE TO HEAVY RAINFALL
AMOUNTS. THIS...HOWEVER...WILL BE HIGHLY DEPENDENT ON THE
INTENSITY AND LOCATION OF HURRICANE TEDDY. THE FARTHER NORTH...THE
BETTER THE CHANCES FOR DEVELOPMENT OVER THE ISLAND. LATER IN THE
DAY/EARLY ON SUNDAY THE LOW LEVEL WINDS ARE FORECAST TO VEER TO
THE SOUTH-SOUTHWEST. BUT AS THE UPPER LEVEL TROUGH
WEAKENS...FORCING ALOFT MIGHT NOT BE ENOUGH TO SUSTAIN ORGANIZED
DEEP CONVECTION. SO EXPECTING A SECOND ROUND OF CONVECTION...BUT
NOT AS INTENSE AS ON SATURDAY.

DAVISON...WPC (USA)