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(Caution: Version displayed is not the latest version. - Issued 1119Z Sep 18, 2020)
 
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
719 AM EDT FRI SEP 18 2020

PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM SEP
18/11UTC: NHC IS ISSUING ADVISORIES FOR HURRICANE TEDDY...PLEASE
REFER TO THEIR DISCUSSION FOR DETAILS.

A TUTT LOW TO THE SOUTHEAST OF BERMUDA EXTENDS A TROUGH SOUTH
BOTTOMING OUT JUST NORTH OF THE ISLANDS. AS HURRICANE TEDDY LIFTS
TO THE NORTHWEST IT IS TO STEER THE TUTT SOUTH TOWARDS THE
NORTHEAST CARIBBEAN DURING THE DAY TODAY. DURING THE WEEKEND THE
TUTT LOW STALLS TO THE NORTH WHILE THE BASE OF THE TROUGH IS TO
MEANDER OVER PUERTO RICO-HISPANIOLA. BUT AS IT IS TO REMAIN CUTOFF
FROM THE FLOW...THIS IS EXPECTED TO GRADUALLY WEAKEN LATER DURING
THE WEEKEND/EARLY NEXT WEEK. AT LOW LEVELS...UNDER THE INFLUENCE
OF HURRICANE TEDDY...A LONG FETCH NORTHEASTERLY FLOW IS TO ENVELOP
THE FORECAST AREA THROUGH MIDDAY ON SATURDAY. LATER IN THE DAY THE
WINDS ARE EXPECTED TO SHIFT TO THE SOUTHWEST AS TEDDY INDUCES AN
INVERTED TROUGH OVER THE EASTERN CARIBBEAN.

DURING THE DAY TODAY...THE LONG FETCH NORTHEASTERLY WINDS ARE TO
ENHANCE MOISTURE CONVERGENCE/TOPOGRAPHICALLY INDUCED CONVECTION
ACROSS INTERIOR PORTIONS OF PUERTO RICO...WITH ACTIVITY TO
GRADUALLY STRENGTHEN LATER IN THE DAY AS THE TUTT SETTLES TO THE
NORTH. THE BEST FORCING AND DEEPER CONVECTIVE
INSTABILITY...HOWEVER...ARE EXPECTED ON SATURDAY. IN A MID/UPPER
LEVEL SOUTHWESTERLY FLOW...FOCUS OF THE DIURNAL CONVECTION SHIFTS
FROM CENTRAL TO NORTHEAST PUERTO RICO DURING THE DAY...WITH THE
CONSENSUS OF THE MODELS SHOWING AN ENHANCED RISK OF MODERATE TO
HEAVY RAINFALL AMOUNTS. BUT AS THE TUTT STARTS TO WEAKEN ON
SUNDAY...DIURNAL ACTIVITY IS FORECAST TO EBB WHILE FOCUSING ALONG
THE NORTH COAST OF PUERTO RICO.

EARLY NEXT WEEK...A MID LEVEL RIDGE BRANCHING FROM THE EAST ACROSS
THE ISLAND CHAIN WILL HELP SUSTAIN THE WEST-SOUTHWESTERLY FLOW
ACROSS THE FORECAST AREA...WHILE AT LOW LEVELS A LONG FETCH
SOUTH-SOUTHWESTERLY FLOW IS TO PERSIST. THIS WILL HELP SUSTAIN A
MOIST ADVECTIVE PATTERN...BRINGING DEEPER MOISTURE TO PUERTO RICO
AND THE VIRGIN ISLES. THIS WILL BE ACCOMPANIED BY A GRADUAL
INCREASE IN CONVECTIVE INSTABILITY...WITH THE GFS SOLUTION BEING
MORE BULLISH THAN THE ECMWF. HOWEVER...DURING THE LATER PERIODS
THE CFS IS SHOWING MJO PATTERN BECOMING MORE HOSTILE TO
DEVELOPMENT...SO WE ARE NOT TOO OPTIMISTIC THAT IT IS GOING TO BE
AS FAVORABLE AS THE GFS SUGGESTS.

DAVISON...WPC (USA)