ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM HURRICANE FLORENCE DISCUSSION NUMBER 29 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 500 PM EDT SUN SEP 10 2006 THE SATELLITE APPEARANCE OF FLORENCE HAS NOT CHANGED APPRECIABLY SINCE THIS MORNING. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REPORTED ONLY A 1-2 MB DECREASE IN THE MINIMUM CENTRAL PRESSURE FROM 12 HOURS AGO. HOWEVER...THEY FOUND A PEAK FLIGHT LEVEL WINDS OF 96 KT...WHICH IS STRONGER THAN WAS OBSERVED OVERNIGHT. THE QUESTION REMAINS AS TO HOW MUCH OF THESE WINDS ARE REACHING THE SURFACE. DROPSONDE DATA THUS FAR SUGGESTS THAT THE REDUCTION FACTOR IS BETWEEN 80 AND 85 PERCENT FROM THE 700 MB FLIGHT LEVEL WINDS...A LITTLE LOWER THAN THE STANDARD 90 PERCENT. THEREFORE...THE INITIAL INTENSITY IS SET AT 80 KT. THE INNER CORE IS SOMEWHAT RAGGED-LOOKING ON SATELLITE IMAGERY AND RECONNAISSANCE OBSERVATIONS DO NOT INDICATE A WELL DEVELOPED EYEWALL. NONETHELESS...THE INTENSITY GUIDANCE INDICATES SOME ADDITIONAL STRENGTHENING...LIKELY TO A CATEGORY 2 HURRICANE BEFORE THE CENTER NEARS BERMUDA IN ABOUT 12-24 HOURS. AFTERWARDS... INCREASING SOUTHWESTERLY SHEAR AND COOLER SSTS SHOULD GRADUALLY WEAKENING FLORENCE. THE HURRICANE IS STILL FORECAST TO BECOME A VERY LARGE AND POWERFUL EXTRATROPICAL CYCLONE IN ABOUT 72 HOURS. THE INITIAL MOTION IS 350/11. THE TRACK GUIDANCE REMAINS IN FAIRLY GOOD AGREEMENT FOR THE FIRST 36 HOURS...ALTHOUGH IT IS LITTLE SLOWER THAN THE PREVIOUS ADVISORY. AFTER 48 HOURS...THE MODELS SIGNIFICANTLY DIVERGE...WITH THE GFDL...NOGAPS...AND ECMWF DEPICTING A MORE NORTHWARD TRACK TOWARD NEWFOUNDLAND. OUT OF RESPECT FOR THESE MODELS...THE OFFICIAL FORECAST TRACK WAS ADJUSTED WESTWARD...A LITTLE CLOSER TO NEWFOUNDLAND. THE GFS AND UKMET REMAIN ON THE EASTERN SIDE OF THE MODEL GUIDANCE...WITH THE GFS MUCH FASTER THAN ALL AVAILABLE GUIDANCE. THE OFFICIAL FORECAST REMAINS NEAR THE MODEL CONSENSUS AND THE FSU SUPERENSEMBLE...BUT IS MUCH SLOWER THAN THE GFS. GIVEN THE LARGE MODEL SPREAD AT DAYS 4 AND 5...THERE IS RATHER LOW CONFIDENCE IN THE FORECAST AT THOSE TIME RANGES. FORECAST POSITIONS AND MAX WINDS INITIAL 10/2100Z 29.9N 66.2W 80 KT 12HR VT 11/0600Z 31.3N 66.1W 90 KT 24HR VT 11/1800Z 33.6N 65.1W 95 KT 36HR VT 12/0600Z 36.0N 63.6W 90 KT 48HR VT 12/1800Z 38.6N 61.6W 80 KT 72HR VT 13/1800Z 45.0N 55.0W 65 KT...EXTRATROPICAL 96HR VT 14/1800Z 48.0N 45.0W 60 KT...EXTRATROPICAL 120HR VT 15/1800Z 48.0N 34.0W 50 KT...EXTRATROPICAL $$ FORECASTER BROWN/PASCH NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:37 UTC