[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 310849
TCDAT2

TROPICAL STORM LESLIE DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
500 AM AST FRI AUG 31 2012

WATER VAPOR IMAGERY SUGGESTS THAT THE EASTERLY SHEAR THAT HAS BEEN
AFFECTING LESLIE IS GRADUALLY SUBSIDING.  THE STORM IS PRODUCING
GOOD OUTFLOW IN ALL QUADRANTS...AND IT APPEARS THAT THE LOW-LEVEL
CENTER HAS MIGRATED FARTHER INTO THE CONVECTIVE CANOPY.  DVORAK
ESTIMATES HAVE INCREASED TO T3.5 FROM BOTH TAFB AND SAB...AND THE
INITIAL INTENSITY IS RAISED TO 55 KT.

LESLIE IS CURRENTLY MOVING AT 285/14 KT...AND A WEST-NORTHWESTWARD
MOTION SHOULD CONTINUE AS THE CYCLONE APPROACHES A BREAK IN THE
SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC.  THE RIDGE IS FORECAST
TO NEARLY VANISH BY DAY 3 AS LESLIE BECOMES POSITIONED BETWEEN TWO
MID/UPPER-LEVEL LOWS AND WELL TO THE SOUTH OF THE MID-LATITUDE
WESTERLIES.  BECAUSE OF THE COLLAPSE IN THE STEERING FLOW...LESLIE
IS EXPECTED TO TURN NORTHWARD BUT SLOW DOWN CONSIDERABLY BY DAYS 4
AND 5.  THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO...
BUT THERE HAS BEEN A NOTICEABLE SOUTHWESTWARD SHIFT ON DAYS 4 AND
5.  THE NEW NHC FORECAST IS THEREFORE SLOWER AND FARTHER WEST OF
THE PREVIOUS FORECAST AT THE LATTER END OF THE FORECAST PERIOD...
BUT IT IS STILL EAST OF THE MODEL CONSENSUS TVCA ON DAY 5.

THE UPPER-LEVEL ENVIRONMENT AROUND LESLIE IS IMPROVING...AND THE
GLOBAL MODELS SUGGEST THAT THE STORM SHOULD HAVE AN OUTFLOW PATTERN
BENEFICIAL FOR STRENGTHENING FOR AT LEAST THE NEXT 3 DAYS.  THE
OFFICIAL FORECAST THEREFORE SHOWS STEADY INTENSIFICATION THROUGH 72
HOURS AND ACTUALLY ENDS UP A BIT HIGHER THAN THE INTENSITY
GUIDANCE.  THERE IS SOME DISAGREEMENT AMONG THE MODELS ON DAYS 4
AND 5...HOWEVER.  THE OPERATIONAL GFS MAINTAINS A GOOD UPPER-LEVEL
OUTFLOW PATTERN ON THOSE DAYS...WHILE THE ECMWF...UKMET...GFS
ENSEMBLE MEAN...AND ECMWF ENSEMBLE MEANS ALL SHOW AN INCREASE IN
SHEAR.  THE NHC FORECAST HEDGES ON THE SCENARIO SHOWN BY THE
MAJORITY OF THESE MODELS...AS WELL AS THE STATISTICAL-DYNAMICAL
GUIDANCE...AND INDICATES SOME POSSIBLE WEAKENING ON DAYS 4 AND 5.


FORECAST POSITIONS AND MAX WINDS

INIT  31/0900Z 15.2N  47.8W   55 KT  65 MPH
 12H  31/1800Z 16.1N  50.0W   65 KT  75 MPH
 24H  01/0600Z 17.4N  52.7W   70 KT  80 MPH
 36H  01/1800Z 18.6N  55.2W   80 KT  90 MPH
 48H  02/0600Z 19.9N  57.4W   85 KT 100 MPH
 72H  03/0600Z 23.0N  60.5W   90 KT 105 MPH
 96H  04/0600Z 25.5N  62.0W   85 KT 100 MPH
120H  05/0600Z 27.0N  62.0W   80 KT  90 MPH

$$
FORECASTER BERG



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