KATE #18 - DISCUSSION

[AussieMark]

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WTNT41 KNHC 300251
TCDAT1
HURRICANE KATE DISCUSSION NUMBER 18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 29 2003

THE MOST RECENT QUIKSCAT PASS...AT 21Z...CONTAINED AN UNCONTAMINATED
65 KT VECTOR IN THE SOUTHEAST QUADRANT...AND TWO FLAGGED 65 KT
VECTORS WHICH I ALSO ACCEPT AS VALID. ON THE BASIS OF THESE
DATA...KATE IS UPGRADED TO A HURRICANE. GIVEN THE RESOLUTION OF
THIS INSTRUMENT...THE ACTUAL PEAK WINDS MIGHT EVEN HAVE BEEN A BIT
HIGHER. SINCE THE TIME OF THE PASS THE ORGANIZATION OF THE SYSTEM
HAS DIMINISHED SOMEWHAT...WITH A MICROWAVE PASS AT 2330Z CLEARLY
SHOWING A SHEARED STRUCTURE. HOWEVER...RECENT WATER VAPOR IMAGERY
SHOWS OUTFLOW IS BEGINNING TO DEVELOP IN THE NORTH QUADRANT.

THE INITIAL MOTION IS 055/14...A LITTLE SLOWER THAN BEFORE...BUT
KATE IS NOT SLOWING AS FAST AS PREVIOUSLY FORECAST. THE ONLY THING
I AM CONFIDENT OF REGARDING THE FORECAST TRACK IS THAT THE OFFICIAL
FORECAST WILL PROBABLY HAVE LARGE ERRORS. KATE IS EMBEDDED IN A
HIGH-SHEAR ENVIRONMENT AND THE TRACK GUIDANCE IS EXTREMELY
DIVERGENT. IN SUCH AN ENVIRONMENT THE TRACK CAN BE HIGHLY DEPENDENT
ON THE VERTICAL COHERENCE OF THE VORTEX...SOMETHING THAT IS RATHER
DIFFICULT TO PREDICT. STILL...THERE IS A COLLECTION OF GUIDANCE
THAT SHARPLY TURNS KATE TO THE NORTHWEST AROUND THE UPPER-LEVEL LOW
SEEN IN WATER-VAPOR IMAGERY TO THE NORTHWEST OF THE HURRICANE. THE
GFS...WHICH HAD AN EASTWARD TRACK IN THE 12Z RUN...IS BACK AGAIN
WITH A WEST TRACK IN THE 18Z RUN. OF THE MAJOR MODELS...ONLY THE
UKMET RESISTS THE WESTWARD TURN. THE OFFICIAL FORECAST IS SIMILAR
TO THE PREVIOUS ONE BUT SLIGHTLY SLOWER WITH THE TURN AND SLIGHTLY
FASTER WITH THE SUBSEQUENT WESTWARD MOTION.

AS KATE SLOWS...THE MID-LEVEL FLOW WILL LESSEN BEFORE THE UPPER FLOW
DOES...AND SO I EXPECT INCREASING SEPARATION BETWEEN THE CENTER AND
THE DEEP CONVECTION. THE OFFICIAL FORECAST THEREFORE HAS SOME
WEAKENING IN THE SHORT TERM. AS KATE TURNS BACK TO THE WEST THE
UPPER FLOW SHOULD BECOME MORE DIFLUENT AND THE SHEAR SHOULD
DIMINISH...WHICH WOULD ALLOW STRENGTHENING. NEAR THE END OF THE
FORECAST PERIOD...COOLER SSTS AND UNFAVORABLE ATMOSPHERIC
THERMODYNAMICS ARE EXPECTED TO WEAKEN THE CYCLONE.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 30/0300Z 30.4N 35.0W 65 KT
12HR VT 30/1200Z 31.0N 34.6W 60 KT
24HR VT 01/0000Z 31.5N 34.5W 60 KT
36HR VT 01/1200Z 32.0N 34.7W 65 KT
48HR VT 02/0000Z 32.5N 36.0W 70 KT
72HR VT 03/0000Z 32.5N 37.5W 70 KT
96HR VT 04/0000Z 33.0N 40.0W 65 KT
120HR VT 05/0000Z 34.0N 43.5W 60 KT