[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 090244
TCDAT2

HURRICANE KATIA DISCUSSION NUMBER  44
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 PM AST THU SEP 08 2011

THE CONVECTIVE PATTERN OF KATIA HAS IMPROVED SIGNIFICANTLY DURING
THE PAST 6 HOURS...AND AN EYE HAS BECOME APPARENT AND EMBEDDED
WITHIN A SHIELD OF CLOUD TOPS OF -60C AND COLDER. NHC AODT
SATELLITE INTENSITY ESTIMATES FOR A LARGE RAGGED EYE FEATURE ARE
75-80 KT. GIVEN THAT THE OVERALL STRUCTURE IS BETTER NOW THAN IT
WAS ON THE PREVIOUS ADVISORY...THE INITIAL INTENSITY WILL BE
MAINTAINED AT 75 KT FOR THIS ADVISORY...WHICH MIGHT BE A LITTLE
CONSERVATIVE. UPPER-LEVEL OUTFLOW IS EXCELLENT IN ALL QUADRANTS.

KATIA IS MOVING TO THE NORTHEAST NOW...AND THE INITIAL MOTION
ESTIMATE IS 035/18. KATIA HAS ROUNDED THE WESTERN PERIPHERY OF A
LARGE SUBTROPICAL RIDGE ORIENTED EAST-WEST ALONG 33N LATITUDE AND
IS BEGINNING TO ACCELERATE. ALL OF THE NHC MODEL GUIDANCE IS IN
VERY GOOD AGREEMENT THAT KATIA WILL CONTINUE TO MOVE NORTHEASTWARD
WITH A GRADUAL INCREASE IN FORWARD SPEED FOR THE NEXT 24-36 HOURS.
ONCE THE CYCLONE PASSES NORTH OF 40N LATITUDE...IT IS EXPECTED TO
GET CAUGHT UP IN VERY FAST WESTERLIES FOR THIS TIME OF THE YEAR AND
ACCELERATE TO THE EAST-NORTHEAST AND EAST AT FORWARD SPEEDS OF NEAR
50 KT. ONCE KATIA MOVES OVER MUCH COLDER WATER BY 36 HOURS... THE
COMBINATION OF THE FAST MID-LATITUDE FLOW AND SSTS LESS THAN 21C
ARE EXPECTED TO RESULT IN THE TROPICAL CYCLONE MAKING THE
TRANSITION INTO A POWERFUL EXTRATROPICAL CYCLONE. THE OFFICIAL
FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY...AND CLOSELY
FOLLOWS THE NHC CONSENSUS MODELS TVCN AND TVCA.

NOW THAT KATIA HAS TURNED TO THE NORTHEAST...THE VERTICAL SHEAR HAS
DECREASED AND IT IS EXPECTED TO REMAIN LESS THAN 10 KT FOR THE NEXT
24 HOURS OR SO. THIS SHOULD ALLOW KATIA TO AT LEAST MAINTAIN ITS
CURRENT INTENSITY...ESPECIALLY SINCE DOWNSTREAM BUOYS AHEAD OF THE
CYCLONE ARE INDICATING SSTS OF 27-28C SOUTH OF 40N LATITUDE. BY 36
HOURS...EXTRATROPICAL TRANSITION IS EXPECTED...BUT KATIA IS STILL
FORECAST TO HAVE HURRICANE-FORCE WINDS...WHICH WILL BE AIDED BY
UNUSUALLY FAST FORWARD SPEEDS ABOVE 35 KT BEYOND 36 HOURS.

ALTHOUGH KATIA IS FORECAST TO EVENTUALLY LOSE ITS TROPICAL
CHARACTERISTICS...THIS CYCLONE IS EXPECTED TO REMAIN A VERY
POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM THAT COULD BRING VERY
STRONG WINDS TO THE BRITISH ISLES BY MONDAY.

FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 36.3N  68.8W   75 KT  85 MPH
 12H  09/1200Z 38.1N  66.5W   75 KT  85 MPH
 24H  10/0000Z 40.5N  61.1W   70 KT  80 MPH
 36H  10/1200Z 42.9N  52.6W   70 KT  80 MPH...POST-TROP/EXTRATROP
 48H  11/0000Z 46.4N  39.5W   65 KT  75 MPH...POST-TROP/EXTRATROP
 72H  12/0000Z 54.1N  16.7W   60 KT  70 MPH...POST-TROP/EXTRATROP
 96H  13/0000Z 61.0N   4.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  14/0000Z...ABSORBED

$$
FORECASTER STEWART



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