ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:59 UTC