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Chill falls over the Atlantic as the official season heads towards close
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| #42676 (Received by flhurricane at: 10:53 PM 28.Aug.2005) TCDAT2 HURRICANE KATRINA DISCUSSION NUMBER 25 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT SUN AUG 28 2005 THERE ARE CONFLICTING SIGNALS REGARDING THE INTENSITY OF KATRINA. THE NOAA AIRCRAFT NEAR 00Z REPORTED A PEAK FLIGHT LEVEL WIND OF 155 KT...WHICH WOULD NORMALLY CORRESPOND TO 140 KT AT THE SURFACE. THE PRESSURE REMAINS EXTREMELY LOW...904 MB AT LAST REPORT. ON THE OTHER HAND...THE STEPPED-FREQUENCY MICROWAVE RADIOMETER...OR SFMR...SUGGESTED WINDS WERE IN THE 120-130 KT RANGE...AND LIMITED DROPSONDE DATA ALSO SUGGESTED SOMETHING A LITTLE BELOW 140 KT. THERE ARE ENOUGH QUESTIONS ABOUT THE PERFORMANCE OF THE SFMR AT THESE SPEEDS FOR ME TO STICK WITH THE STANDARD 90 PERCENT ADJUSTMENT FOR NOW. THERE HAVE BEEN SOME MODEST CHANGES IN THE STRUCTURE OF KATRINA OVER THE LAST SEVERAL HOURS. RECENT MICROWAVE PASSES SHOW THAT AN OUTER EYEWALL IS IN THE FORMATIVE STAGES...AND THE LATEST IR IMAGES SHOW A LESS WELL-DEFINED EYEWALL WITH MORE EVIDENCE OF OUTER BANDING. THE NOAA HURRICANE HUNTERS ALSO REPORTED AN EROSION OF THE EYEWALL IN THE SOUTHWEST QUADRANT. THESE OBSERVATIONS SUGGEST THAT THERE COULD BE SOME WEAKENING OF KATRINA PRIOR TO LANDFALL. ALL THIS IS RELATIVE...HOWEVER...AND KATRINA IS STILL EXPECTED TO BE OF AT LEAST CATEGORY FOUR INTENSITY WHEN IT REACHES THE COAST. AN EYEWALL REPLACEMENT AT THIS POINT IS NOT ALL GOOD NEWS...AS THEY ARE GENERALLY ACCOMPANIED BY A BROADENING OF THE WIND FIELD...SO THAT EVEN AS KATRINA WEAKENS THERE COULD BE AN INCREASE IN THE AREA THAT EXPERIENCES MAJOR HURRICANE FORCE WINDS. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE TRACK FORECAST. THE INITIAL MOTION IS 335/9. KATRINA IS EXPECTED TO GRADUALLY TURN NORTHWARD INTO A BREAK IN THE SUBTROPICAL RIDGE ASSOCIATED WITH A LARGE MID-LATITUDE CYCLONE NEAR THE GREAT LAKES. MODEL GUIDANCE REMAINS TIGHTLY CLUSTERED...WITH THE NOGAPS SHIFTING JUST A BIT EAST OF ITS PREVIOUS TRACK. WHILE THERE IS GREAT SIGNIFICANCE FOR THE CITY OF NEW ORLEANS IN THE DETAILS OF THE TRACK...TRACK ANOMOLIES OF 30-50 MILES ARE STILL POSSIBLE EVEN 12-18 HOURS OUT. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 29/0300Z 27.6N 89.4W 140 KT 12HR VT 29/1200Z 29.2N 89.7W 135 KT 24HR VT 30/0000Z 31.8N 89.5W 85 KT...INLAND 36HR VT 30/1200Z 34.8N 88.1W 45 KT...INLAND 48HR VT 31/0000Z 37.7N 85.9W 30 KT...INLAND 72HR VT 01/0000Z 43.5N 78.5W 25 KT...INLAND 96HR VT 02/0000Z 50.0N 70.0W 25 KT...EXTRATROPICAL 120HR VT 03/0000Z...ABSORBED |
