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| #9509 (Received by flhurricane at: 4:46 AM 22.Sep.2004) TCDAT1 HURRICANE JEANNE DISCUSSION NUMBER 35 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT WED SEP 22 2004 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REPORTED A CENTRAL PRESSURE OF 968 MB AT 0609Z WITH MAXIMUM FLIGHT-LEVEL WINDS OF 83 KT AT 700 MB IN THE SOUTHWESTERN EYEWALL. A DROPSONDE IN THE NORTHWESTERN EYEWALL SUGGESTED SURFACE WINDS OF ABOUT 80 KT. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN 77 KT...AND THE MAXIMUM INTENSITY WILL REMAIN 80 KT. ANALYSES FROM CIMMS AT THE UNIVERSITY OF WISCONSIN INDICATE 15-20 KT OF WEST-SOUTHWESTERLY VERTICAL SHEAR...AND WATER VAPOR IMAGERY SHOWS A LOT OF DRY AIR SURROUNDING JEANNE. SOME DRY AIR MAY HAVE REACHED THE SOUTHWESTERN EYEWALL BASED ON THE AIRCRAFT DATA. THE INITIAL MOTION IS 180/3. WATER VAPOR IMAGERY SHOWS A DEEP LAYER TROUGH NORTHEAST OF JEANNE AND A LARGE-DEEP LAYER RIDGE CENTERED OVER THE CENTRAL GREAT LAKES...WITH STRONG NORTHERLY FLOW BETWEEN THE TWO FEATURES TO THE NORTH OF JEANNE. LARGE-SCALE MODELS FORECAST THE RIDGE BUILD OR MOVE EASTWARD INTO THE ATLANTIC DURING THE NEXT 3-4 DAYS...WITH HEIGHTS FALLING OVER THE EASTERN UNITED STATES BY DAYS 4-5. THIS EVOLUTION SHOULD START JEANNE ON A GENERAL WESTERLY TRACK IN 24 HR OR SO...THEN CAUSE A MORE NORTHWARD MOTION AFTER 72-96 HR. TRACK FORECAST GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT...WITH ALL THE DYNAMICAL MODELS...INCLUDING THE GFS...AGREEING WITH THIS SCENARIO. THE OFFICIAL FORECAST TRACK IS SHIFTED SOUTHWARD DURING THE FIRST 36 HR...THEN IS SHIFTED CONSIDERABLY TO THE WEST FROM THE PREVIOUS PACKAGE DURING THE REST OF THE FORECAST PERIOD. THE NEW TRACK IS JUST TO THE RIGHT OF THE MODEL CONSENSUS. IT IS POSSIBLE THE FORECAST TRACK MAY HAVE TO BE SHIFTED FARTHER WEST ON SUBSEQUENT ADVISORIES. WHILE THE TRACK FORECAST IS MORE CLEAR-CUT...THE INTENSITY FORECAST REMAINS PROBLEMATIC. LARGE-SCALE MODELS SUGGEST THE CURRENT SHEAR MAY SUBSIDE AS A CUT-OFF LOW OR SHARP CYCLONIC SHEAR AXIS FORMS NEAR FLORIDA IN ABOUT 24 HR. INDEED...THE UPPER-LEVEL WINDS MAY BECOME SOUTHEASTERLY OVER JEANNE. HOWEVER...IT IS NOT TOTALLY CLEAR WHETHER THIS SYSTEM WILL ACT AS AN OUTFLOW CHANNEL OR JUST CHANGE THE DIRECTION OF THE SHEAR. BY 48 HR... AN UPPER-LEVEL ANTICYCLONE SHOULD DEVELOP OVER JEANNE PROVIDING A MORE FAVORABLE ENVIRONMENT. HOWEVER...NONE OF THE INTENSITY FORECAST MODELS... EVEN EXPERIMENTAL ONES...FORECAST AN INTENSITY ABOVE 95 KT. THE REASONS FOR THIS ARE UNCLEAR...BUT IT COULD BE THAT THE DRY AIR IS RESTRAINING THE DEVELOPMENT. THE INTENSITY FORECAST WILL CALL FOR MODEST STRENGTHENING...BUT IT WOULD NOT BE A SURPRISE TO SEE JEANNE GET STRONGER THAN CURRENTLY FORECAST IN 72-96 HR. THE MODELS HAVE BACKED OFF A BIT ON THE SHEAR IN THE 96-120 HR TIMEFRAME...SO THE FORECAST WILL SHOW LESS WEAKENING AT THAT TIME. THE NEW FORECAST TRACK INCREASES THE THREAT TO THE SOUTHEASTERN COAST OF THE UNITED STATES. HOWEVER...IT IS TOO EARLY TO TELL WHICH PART OF THE COAST...IF ANY...MAY BE AFFECTED BY JEANNE. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 22/0900Z 26.6N 68.6W 80 KT 12HR VT 22/1800Z 26.3N 68.8W 80 KT 24HR VT 23/0600Z 26.1N 69.5W 85 KT 36HR VT 23/1800Z 26.1N 70.5W 85 KT 48HR VT 24/0600Z 26.3N 71.8W 85 KT 72HR VT 25/0600Z 27.0N 74.5W 85 KT 96HR VT 26/0600Z 29.0N 77.0W 75 KT 120HR VT 27/0600Z 32.0N 78.0W 65 KT |
