[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 061441
TCDAT2

HURRICANE LESLIE DISCUSSION NUMBER  29
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
1100 AM AST THU SEP 06 2012

SATELLITE INTENSITY ESTIMATES SUGGEST THAT THE CYCLONE IS BARELY A
HURRICANE WITH AN INITIAL INTENSITY OF 65 KNOTS. LESLIE HAS A VERY
LARGE CIRCULATION BUT LACKS AN INNER CORE.  MOST OF THE THUNDERSTORM
ACTIVITY IS CONCENTRATED IN CYCLONICALLY CURVED BANDS TO THE NORTH
AND EAST OF THE CENTER DUE TO WESTERLY WIND SHEAR.  GLOBAL MODELS
HAVE BEEN VERY STUBBORN IN FORECASTING A RELAXATION OF THE SHEAR...
ALTHOUGH THAT HAS NOT MATERIALIZED YET.  HOWEVER...GIVING CREDIT TO
THESE MODELS...AND THE FACT THAT THE SHIPS AND LGEM STATISTICAL
MODELS ALSO DECREASE THE SHEAR...THE NHC FORECAST CALLS FOR
STRENGTHENING TO BEGIN IN ABOUT 24 HOURS.  THIS IS ALSO SUPPORTED
BY THE FACT THAT LESLIE WILL BE MOVING OUT OF THE COOLER WATERS
WHICH RESULTED FROM THE UPWELLING.

LESLIE IS EMBEDDED WITHIN VERY LIGHT STEERING CURRENTS AND
CONSEQUENTLY HAS BEEN MOVING VERY LITTLE OR MEANDERING NORTHWARD
DURING THE PAST SEVERAL HOURS.  THE STEERING CURRENTS ARE NOT
FORECAST TO CHANGE MUCH DURING THE NEXT 24 TO 36 HOURS...BUT MOST
OF THE GLOBAL MODELS BEGIN TO REDEVELOP THE SUBTROPICAL RIDGE TO THE
EAST OF LESLIE AND BRING A LARGE MID-LATITUDE TROUGH OVER THE
EASTERN UNITED STATES.  THIS PATTERN SHOULD FORCE LESLIE TO
MOVE NORTHWARD AND THEN NORTH-NORTHEASTWARD WITH AN INCREASE IN
FORWARD SPEED DURING THE REMAINDER OF THE FORECAST PERIOD.  ALTHOUGH
THE TRACK MODELS ARE NOT IN GOOD AGREEMENT ON THE FORWARD SPEED...
THE GENERAL MODEL TREND IS FOR A NORTHWARD AND NORTH-NORTHEASTWARD
MOTION.  THE WESTERN EDGE OF THE GUIDANCE ENVELOPE IS NEAR BERMUDA
BUT THE CONSENSUS AS WELL AS THE GFS AND THE ECMWF MODELS SHOW A
TRACK EAST OF BERMUDA.

THE WIND FIELD OF LESLIE...COMBINED WITH ITS EXPECTED SLOW MOTION...
WILL GENERATE LONG-PERIOD SWELLS THAT WILL PRODUCE LARGE WAVES AND
LIFE-THREATENING RIP CURRENTS ON BERMUDA AND ALONG MUCH OF THE U.S.
EAST COAST FOR THE REMAINDER OF THIS WEEK.

FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 26.4N  62.4W   65 KT  75 MPH
 12H  07/0000Z 26.5N  62.4W   65 KT  75 MPH
 24H  07/1200Z 26.8N  62.5W   70 KT  80 MPH
 36H  08/0000Z 27.3N  62.8W   80 KT  90 MPH
 48H  08/1200Z 28.2N  63.0W   85 KT 100 MPH
 72H  09/1200Z 31.2N  62.8W   90 KT 105 MPH
 96H  10/1200Z 35.0N  61.8W   90 KT 105 MPH
120H  11/1200Z 40.0N  59.0W   80 KT  90 MPH

$$
FORECASTER AVILA


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