Hurricane FLORENCE

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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
 
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