[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 072051
TCDAT2

HURRICANE KATIA DISCUSSION NUMBER  39
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST WED SEP 07 2011

THE CLOUD TOPS ASSOCIATED WITH KATIA WARMED DURING THE EARLY
AFTERNOON...BUT SINCE THAT TIME A NEW BURST OF DEEP CONVECTION
HAS FORMED TO THE NORTHEAST OF THE CENTER.  AN EARLIER TRMM PASS
ONCE AGAIN SHOWED A SMALL REMNANT OF THE INNER EYEWALL WITH A LARGE
BAND OF CONVECTION OVER THE NORTH AND EAST SEMICIRCLES OF THE
CIRCULATION.  SUBJECTIVE AND OBJECTIVE DVORAK T- AND CI-NUMBERS
CONTINUE TO SLOWLY DECREASE...THEREFORE THE INITIAL INTENSITY IS
LOWERED TO 70 KT.  THERE HAS BEEN LITTLE CHANGE TO THE INTENSITY
FORECAST REASONING.  MODERATE WESTERLY SHEAR CURRENTLY OVER THE
SYSTEM IS FORECAST TO DECREASE ON THURSDAY...HOWEVER THIS IS LIKELY
TO BE NEGATED BY SLIGHTLY COOLER SSTS THAT THE HURRICANE WILL BE
MOVING OVER.  OVERALL...LITTLE CHANGE IN STRENGTH IS FORECAST
DURING THE NEXT COUPLE OF DAYS.  KATIA IS EXPECTED TO BECOME A
LARGE AND POWERFUL EXTRATROPICAL CYCLONE IN ABOUT 72 HOURS.

THE INITIAL MOTION ESTIMATE IS 320/9.  THE MODELS REMAIN IN VERY
GOOD AGREEMENT MOVING KATIA AROUND THE WEST SIDE OF A
MID/UPPER-LEVEL RIDGE OVER THE CENTRAL ATLANTIC DURING THE NEXT
24-36 HOURS.  AFTER 48 HOURS...THE CYCLONE IS EXPECTED TO
ACCELERATE NORTHEASTWARD AHEAD OF A BROAD TROUGH MOVING ACROSS
THE CANADIAN MARITIMES.  THE GFS AND ECMWF MODELS ARE STILL IN
REMARKABLY GOOD AGREEMENT ON THE EXTRATROPICAL PORTION OF THE
TRACK.  THE OFFICIAL FORECAST HAS BEEN NUDGED NORTHWARD AT 36 HOURS
AND BEYOND AND IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE.


FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 29.9N  69.7W   70 KT  80 MPH
 12H  08/0600Z 31.3N  70.1W   70 KT  80 MPH
 24H  08/1800Z 33.8N  70.0W   70 KT  80 MPH
 36H  09/0600Z 36.6N  68.5W   70 KT  80 MPH
 48H  09/1800Z 39.2N  64.5W   70 KT  80 MPH
 72H  10/1800Z 44.5N  46.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  11/1800Z 53.0N  26.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
120H  12/1800Z 60.0N   7.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
FORECASTER BROWN


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