ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 35 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT SUN SEP 14 2003 THE AFTERNOON PLETHORA OF RECON WIND AND PRESSURE DATA INDICATE THAT ISABEL REMAINS BARELY BELOW CATEGORY 5 INTENSITY. AIR FORCE RESERVE HURRICANE HUNTERS MEASURED 700 MB FLIGHT-LEVEL WINDS OF 150 KT...OR 135 KT SURFACE EQUIVALENT...IN THE NORTHEAST QUADRANT OF THE EYEWALL...WHILE A NOAA HURRICANE HUNTER DROPSONDE REPORT INDICATED 171 KT AVERAGE WINDS IN THE LOWER 150 METERS...OR 139 SURFACE WIND EQUIVALENT. BASED ON THIS INFORMATION...ISABEL IS BEING MAINTAINED AT 135 KT. THE OUTFLOW PATTERN REMAINS VERY IMPRESSIVE AND HAS CONTINUED TO EXPAND. THE INITIAL MOTION ESTIMATE IS 290/11. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS 2 FORECAST TRACKS OR REASONINGS. RECON FIX POSITIONS HAVE BEEN COMING IN RIGHT ON TRACK AND THE LATEST 12Z NHC MODEL GUIDANCE CONTINUES TO CONVERGE ABOUT THE PREVIOUS 2 FORECAST TRACKS. THE LATEST GFDL RUN HAS CONTINUED ITS WESTWARD SHIFT IN THE FORECAST TRACK AND THE 96-120H TRACK IS AT LEAST 90 NMI WEST OF THE 00Z TRACK. ONE DISTURBING BIT OF INFORMATION IS THAT THE 12Z UKMET... GFS...GFDL...AND CANADIAN MODELS DID NOT ANALYZE THE 500 MB HEIGHT AND WIND FIELDS TO THE 12Z BERMUDA UPPER-AIR OBSERVATION OF 10 KT NORTHEAST WIND AND 5940 METER HEIGHT. THIS OBSERVATION SUGGESTS THAT THE RIDGE TO THE NORTH OF BERMUDA AND ISABEL EXTENDS SOUTHWESTWARD FARTHER THAN THOSE FOUR MODELS ARE INDICATING. MORE RIDGING WOULD SUGGEST THAT...AT LEAST IN THE SHORT TERM... ISABEL SHOULD MOVE FARTHER WEST THAN THESE MODELS ARE FORECASTING BEFORE THE HURRICANE BEGINS TO TURN NORTHWESTWARD. ONLY THE NOGAPS MODEL INITIALIZED THE 500 MB PROPERLY TO THE BERMUDA OBSERVATION...AND THE 12Z NOGAPS TRACK IS TO THE LEFT OR WEST OF THE PREVIOUS AND CURRENT FORECAST TRACKS. THE OFFICIAL FORECAST TRACK IS JUST AN EXTENSION OF THE PREVIOUS TRACK AND IS A LITTLE TO THE WEST AND SLIGHTLY FASTER THAN THE MODEL CONSENSUS. THERE REMAINS SOME UNCERTAINTY ON WHERE THE EXACT LANDFALL OF ISABEL COULD OCCUR SINCE THE DEVELOPING CENTRAL U.S. TROUGH COULD STILL DEEPEN AND DIG MORE SOUTHWARD THAN THE MODELS ARE INDICATING. THIS COULD INDUCE A MORE NORTHWARD MOTION AND RESULT IN LANDFALL FARTHER UP THE U.S. EAST COAST. BUT AS IN THE PREVIOUS SEVERAL MODEL RUNS...A LARGE AND VERY STRONG NORTH-SOUTH ORIENTED RIDGE IS FORECAST TO REMAIN EAST OF ISABEL AND PREVENT THE HURRICANE FROM RECURVING NORTHEASTWARD. ONLY MINOR FLUCTUATIONS IN INTENSITY ARE EXPECTED FOR THE NEXT COUPLE OF DAYS AS ISABEL IS FORECAST TO MOVE OVER SIGHTLY WARMER WATER AND REMAIN IN A FAVORABLE UPPER-LEVEL OUTFLOW PATTERN. BY 96 HOURS...ISABEL IS FORECAST TO BEGIN ACCELERATING NORTH OR NORTH-NORTHWESTWARD UNDER INCREASING SOUTHERLY UPPER-LEVEL FLOW. HOWEVER...THE CENTRAL CORE OF ISABEL IS EXPECTED TO REMAIN EAST OF THE STRONGEST WINDS AND UNDER 15-25 KT 200 MB FLOW. THIS WOULD TEND TO KEEP ISABEL STRONGER THAN WHAT THE SHIPS INTENSITY MODEL HAS BEEN INDICATING...ESPECIALLY SINCE ISABEL WILL BE MOVING OVER THE WARM GULFSTREAM OFFSHORE NORTH CAROLINA JUST PRIOR TO LANDFALL. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 14/2100Z 24.1N 67.4W 135 KT 12HR VT 15/0600Z 24.7N 68.9W 135 KT 24HR VT 15/1800Z 25.7N 70.2W 135 KT 36HR VT 16/0600Z 26.7N 71.3W 130 KT 48HR VT 16/1800Z 28.0N 72.2W 125 KT 72HR VT 17/1800Z 31.2N 74.0W 120 KT 96HR VT 18/1800Z 36.5N 76.0W 105 KT 120HR VT 19/1800Z 43.5N 78.0W 35 KT...INLAND NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:58 UTC