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| #8048 (Received by flhurricane at: 5:09 PM 12.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 42 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT SUN SEP 12 2004 THE INITIAL MOTION ESTIMATE IS 295/09 OVER THE PAST 12 HOURS. IVAN HAS WOBBLED A LITTLE LEFT OF TRACK...SO THE FORECAST TRACK WAS SHIFTED WESTWARD...ESPECIALLY IN THE FIRST 24 HOURS. THE NHC MODEL CONSENSUS HAS ALSO SHIFTED SLIGHTLY WESTWARD...ALTHOUGH SOME OF THE INDIVIDUAL MODELS HAVE SWAPPED POSITIONS...WITH THE UKMET SHIFTING EASTWARD WHILE NOGAPS SHIFTED WESTWARD. THE LATEST 18Z UPPER-AIR DATA INDICATE A SHARP SHORTWAVE TROUGH OVER THE SOUTH CENTRAL U.S. HAS CONTINUED TO PUSH SLOWLY SOUTHEASTWARD INTO THE CENTRAL GULF OF MEXICO. THIS HAS ERODED THE MID-LEVEL RIDGE ALONG 90W LONGITUDE... AND THE SLOW EASTWARD EROSION SHOULD CONTINUE FOR THE NEXT 24-48 HOURS. THIS SHOULD ALLOW IVAN TO SLOWLY MOVE NORTHWESTWARD TO NEAR WESTERN CUBA AND THEN TURN MORE NORTHWARD BY 36 HOURS AFTER THE HURRICANE EMERGES OVER THE SOUTHEASTERN GULF OF MEXICO. THE FORECAST TRACK IS SIMILAR TO THE GFS AND UKMET SOLUTIONS...AND REMAINS TO THE RIGHT OF THE NHC MODEL CONSENSUS. THE CURRENT INTENSITY WAS DECREASED TO 130 KT BASED ON RECENT AIR FORCE AND NOAA RECON REPORTS. HAVING SAID THAT...A NEW RECON REPORT INDICATES THE PRESSURE HAS DECREASED 4 MB IN THE PAST 2 HOURS DOWN TO 916 MB. THE OUTER CONCENTRIC EYEWALL HAS ALSO DECREASED FROM 60 NMI DOWN TO 30 NMI DURING THE PAST 6 HOURS...SO THE RECENT PRESSURE FALL IS ABOUT ON TARGET FOR THE OUTER EYEWALL TO BECOME STABLE AROUND 20 NMI. AT THAT POINT...RE-INTENSIFICATION TO CATEGORY 5 STRENGTH MAY BEGIN LIKE IT DID ABOUT THIS TIME YESTERDAY. THERE WILL CONTINUE TO BE PERIODIC FLUCTUATIONS IN THE INTENSITY...MAINLY DUE TO ADDITIONAL EYEWALL REPLACEMENT CYCLES. BUT THE LOW SHEAR CONDITIONS AND THE VERY WARM SSTS AHEAD OF IVAN SHOULD KEEP THE HURRICANE AT LEAST AT CATEGORY 4 STRENGTH UNTIL THE CENTRAL GULF OF MEXICO IS REACHED IN 36-48 HOURS. SOME COOL UPWELLING IS EXPECTED FROM THAT POINT UNTIL U.S. LANDFALL OCCURS...WHICH SHOULD BRING ABOUT GRADUAL WEAKENING DESPITE THE VERY FAVORABLE UPPER-LEVEL OUTFLOW PATTERN THAT ALL OF THE GLOBAL MODELS ARE FORECASTING. BECAUSE STEERING ARE CURRENTLY WEAK AND MAY WEAKEN EVEN MORE...THERE REMAINS CONSIDERABLE UNCERTAINTY AS TO JUST WHEN AND WHERE...AND AT WHAT INTENSITY...IVAN WILL MAKE LANDFALL IN THE UNITED STATES IN THE LONGER TIME PERIODS. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 12/2100Z 19.3N 82.5W 130 KT 12HR VT 13/0600Z 19.9N 83.5W 140 KT 24HR VT 13/1800Z 21.3N 84.7W 145 KT 36HR VT 14/0600Z 23.1N 85.5W 140 KT 48HR VT 14/1800Z 25.4N 86.0W 125 KT 72HR VT 15/1800Z 28.0N 86.0W 110 KT 96HR VT 16/1800Z 32.5N 85.0W 55 KT...INLAND 120HR VT 17/1800Z 37.5N 81.0W 25 KT...INLAND |
