904 
 WTNT42 KNHC 252108
 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
  
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