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Tropical Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1133Z Sep 15, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
733 AM EDT TUE SEP 15 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM SEP
15/12UTC: NHC IS ISSUING ADVISORIES FOR TROPICAL STORMS TEDDY AND
VICKY. THEY CONTINUE TO FORECAST BOTH TO FOLLOW A TRACK THAT WILL
KEEP THEM FAR TO THE EAST/NORTH...WITH TEDDY EXPECTED TO GRADUALLY
INTENSIFY TO A MAJOR HURRICANE.

TUTT ALOFT CONTINUES TO RELAX ITS FOOTHOLD OVER THE FORECAST AREA
WHILE YIELDING TO A MID/UPPER LEVEL RIDGE BRANCHING INTO THE
NORTHEAST CARIBBEAN. AS IT SETTLES OVER THE FORECAST AREA...THIS
IS TO SUSTAIN A MID LEVEL TRADE WINDS CAP THAT IS TO HOLD THROUGH
AT LEAST THURSDAY MORNING. AT LOW LEVELS...THE EASTERLY TRADES
RETUR TO THE FORECAST AREA AS AN EASTERLY WAVE STREAMS ACROSS THE
EASTERN CARIBBEAN EARLY IN THE CYCLE. CIRAS ADVECTED LAYERED PWAT
PRODUCT SHOWS A SHALLOW PLUME OF MOISTURE IN TANDEM WITH THIS
PERTURBATION. AS IT STREAMS ACROSS PUERTO RICO DURING THE
DAY...EXPECTING SOME ENHANCEMENT TO DIURNAL SHALLOW CONVECTION
ACROSS INTERIOR PORTIONS OF THE ISLAND...WITH MOST INTENSE
CLUSTERING OVER WESTERN INTERIOR IN LATE MORNING TO AFTERNOON
CONVECTION. 

ON WEDNESDAY-EARLY ON THURSDAY...AS THE MID LEVEL RIDGE BRANCHES
OVER THE NORTHEAST CARIBBEAN ISLANDS...PWAT CONTENT IS FORECAST TO
EBB. OVER THE VIRGIN ISLES-EASTERN PUERTO RICO THIS IS TO RESULT
IN MOSTLY FAIR WEATHER CONDITIONS...WHILE OVER INTERIOR PORTIONS
OF PUERTO RICO GROUND MOISTURE WILL BE ENOUGH TO SUSTAIN A ROUND
OF DAYTIME CONVECTION OVER THE ISLAND. DURING THIS PERIOD THE
DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE SHOW POTENTIAL FOR
LOCALLY MODERATE RAINFALL AMOUNTS...WITH MOST ACTIVE CLUSTERING
ALONG THE CORDILLERA.

ON THURSDAY TO FRIDAY THE LOW LEVEL WINDS BACK TO THE NORTHEAST AS
TEDDY INTENSIFIES TO A MAJOR HURRICANE. THIS IS TO THEN STEER THE
REMNANTS OF TROPICAL DEPRESSION RENE ACROSS THE NORTHEAST
CARIBBEAN ON FRIDAY...WITH THE GFS AND UKMET FORECASTING A
STRONGER PERTURBATION THAN WHAT THE ECMWF SUGGESTS. THE GFS AND
UKMET MIGHT BE REACTING TO AN ATMOSPHERIC KELVIN WAVE STREAMING
ACROSS THE BASIN...SO THIS MIGHT BE MORE ACTIVE THAN WHAT THE MEAN
OF THE MODELS SUGGEST. IMPACT THIS MIGHT HAVE OVER THE FORECAST
AREA WILL BE HIGHLY DEPENDENT ON THE INTENSITY AND POSITION OF A
DEEPENING TUTT LATER IN THE WEEK. 

THE GFS AND EUROPEAN GLOBAL MODELS CONTINUE TO DISAGREE ON HOW
THIS TUTT IS GOING TO EVOLVE...WITH THE GFS FAVORING A DEEPER AND
FASTER EVOLUTION THAN WHAT THE EUROPEAN MODELS FORECAST. TROPICAL
CYCLONE TEDDY IS GOING TO HAVE A HUGE IMPACT ON THE UPPER
PATTERN...WITH MASSIVE RELEASE OF LATENT HEAT TO CONTRIBUTE TO
INTENSIFICATION OF THE SUBEQUATORIAL RIDGE TO THE EAST...WHICH IN
TURN COULD LEAD TO A WEAKER TUTT AS THE EUROPEAN MODELS FORECAST.
DURING THE WEEKEND...TEDDY IS TO THEN STEER THE TUTT ALOFT CLOSER
TO THE FORECAST AREA...AS THEY REVOLVE AROUND EACH OTHER IN A
FUJIWHARA FASHION. ENVIRONMENTAL CONDITIONS COULD THEN BECOME MORE
FAVORABLE AS THE TUTT SETTLES TO THE NORTH. HOWEVER...AS TEDDY
INTENSIFIES TO THE NORTH...THE DOWNWARD MOTION ON THE OUTSKIRTS OF
THE CYCLONE MIGHT NEGATE ANY FAVORABLE INFLUENCE THE TUTT MIGHT
HAVE ACROSS THE FORECAST AREA. THUS...CONFIDENCE IN THE FORECAST
REMAINS LOW DURING THE MEDIUM RANGE PERIOD.

DAVISON...WPC (USA)