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| #41890 (Received by flhurricane at: 5:11 PM 25.Aug.2005) TCDAT2 HURRICANE KATRINA DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT THU AUG 25 2005 KATRINA IS NOW A HURRICANE BASED ON NOAA RECON SFMR REPORTS OF SURFACE WINDS TO 64 KT JUST NORTHWEST OF THE CENTER. THESE WINDS ARE SUPPORTED BY NOAA-MIAMI DOPPLER RADAR VELOCITIES OF 90 KT AT 3000 FT...WHICH EQUATES TO ABOUT 67 KT SURFACE WINDS. THE MOST RECENT NOAA RECON PRESSURE WHILE COMPOSING THIS DISCUSSION HAS FALLEN 2 MB IN THE PAST HOUR TO 985 MB. THE INITIAL MOTION ESTIMATE IS 265/5. 12Z AND 18Z UPPER-AIR DATA INDICATE THE SUBTROPICAL RIDGE TO THE NORTH OF KATRINA HAS CHANGED LITTLE WHILE AN INVERTED MID- TO UPPER-LEVEL TROUGH HAS DEVELOPED NORTHWARD FROM THE CARIBBEAN SEA TO KATRINA. THE TROUGH IS EXPECTED TO INDUCE A SLIGHT SOUTH OF DUE WEST MOTION FOR THE NEXT 12 HOURS OR SO. AFTERWARDS...THE RIDGE TO THE NORTH IS EXPECTED TO SLOWLY WEAKEN AND ERODE ON THE WEST SIDE AS A SHORTWAVE TROUGH OVER THE CENTRAL U.S. DIGS SOUTHEASTWARD TOWARD THE NORTHERN GULF OF MEXICO. THIS SLOW EVOLVING PATTERN IS FOECAST TO GRADUALLY INDUCE A SLOW NORTHWEST AND THEN NORTHWARD MOTION AFTER 48 HOURS. THE NHC MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE WESTWARD MOTION FOR THE NEXT 36 HOURS...BUT THEN DIVERGES SIGNIFICANTLY AFTER THAT. THE GFS HAS BEEN THE MOST CONSISTENT/PERSISTENT MODEL IN TAKING KATRINA SLOWLY NORTHEASTWARD AFTER 72 HOURS ACROSS NORTHWEST FLORIDA...WHEREAS THE GFDL...GFDN...AND UKMET MODELS HAVE NOW FLIP-FLOPPED WIDELY TO THE WEST AND BRING KATRINA INLAND BETWEEN MOBILE ALABAMA AND GRAND ISLE LOUISIANA. THE GFDL AND GFDN MODELS HAVE BEEN GIVEN LESS WEIGHT GIVEN THEIR PERSISTENT MUCH FASTER WESTWARD MOTION THE PAST 24 HOURS...WHICH HAS NOT MATERIALIZED. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK AND IS TO THE RIGHT OF THE NHC MODEL CONSENSUS. THERE IS STILL A SHORT WINDOW OF OPPORTUNITY FOR KATRINA TO STRENGTHEN TO AROUND 70 KT BEFORE LANDFALL OCCURS. AFTER LANDFALL ...STEADY WEAKENING IS EXPECTED UNTIL THE HURRICANE EMERGES OFF THE SOUTHWEST FLORIDA COAST IN ABOUT 30 HOURS. ONCE KATRINA MOVES OVER THE WARM GULF OF MEXICO WHERE THE VERTICAL SHEAR IS EXPECTED TO BE LOW...RESTRENGTHENING INTO A HURRICANE SEEMS LIKELY. IT SHOULD BE EMPHASIZED THAT KATRINA IS NOT FORECAST TO WEAKEN PRIOR TO LANDFALL ...WHICH COULD BE IMPLIED BY THE OFFICIAL INTENSITY FORECAST. IN CONTRAST...KATRINA IS EXPECTED TO STRENGTHEN TO 90 KT BEFORE LANDFALL OCCURS IN THE FLORIDA PANHANDLE. THIS IS CONSISTENT WITH THE SHIPS INTENSITY MODEL AND THE TREND IN THE GFDL MODEL... ALTHOUGH THE LATTER MODEL MAKES KATRINA A 118-KT CATEGORY 4 STORM. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 25/2100Z 26.1N 79.9W 65 KT 12HR VT 26/0600Z 26.1N 80.7W 45 KT...INLAND 24HR VT 26/1800Z 26.1N 81.7W 40 KT...INLAND 36HR VT 27/0600Z 26.4N 82.8W 50 KT...OVER WATER 48HR VT 27/1800Z 27.0N 83.7W 60 KT 72HR VT 28/1800Z 28.5N 85.0W 80 KT 96HR VT 29/1800Z 31.5N 84.5W 40 KT...INLAND 120HR VT 30/1800Z 35.0N 81.5W 25 KT...INLAND |
