Hurricane OPHELIA

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HURRICANE OPHELIA DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU SEP 08 2005
 
WSR-88D DOPPLER RADAR VELOCITIES OF 80-85 KT ARE SHOWING UP IN THE
SOUTHERN EYEWALL OF OPHELIA.  THESE WIND SPEEDS ARE AT AN ELEVATION
OF ABOUT 6500 FEET.  USING A STANDARD VERTICAL PROFILE OF WIND
SPEED DETERMINED FROM GPS DROPSONDES IN TROPICAL CYCLONES...THIS
CORRESPONDS TO AT LEAST 65 KT FOR THE SURFACE WIND.  THE AIR FORCE
HURRICANE HUNTERS MEASURED A CENTRAL PRESSURE OF 985 MB BY
DROPSONDE AND THE DROP HAD SURFACE WINDS NEAR 15 KT...SUGGESTING
THAT THE MINIMUM PRESSURE MIGHT BE A LITTLE LOWER THAN THAT VALUE.
BASED ON THESE DATA...OPHELIA IS UPGRADED TO A HURRICANE ON THIS
ADVISORY.  THE HURRICANE HAS WELL-DEFINED UPPER-LEVEL OUTFLOW IN
ALL QUADRANTS EXCEPT THE SOUTHEAST.  VERTICAL SHEAR IS EXPECTED TO
REMAIN MODEST...IN THE 10-15 KT RANGE...BUT SHIPS DIAGNOSES A
RATHER STABLE LAPSE RATE IN THE ENVIRONMENT.  SINCE THE OUTFLOW
LOOKS IMPRESSIVE...AND ASSUMING THAT SLOW-MOVING OPHELIA IS NOT
SIGNIFICANTLY AFFECTED BY COOLER UPWELLED WATERS...ADDITIONAL
STRENGTHENING IS FORECAST.  THE WIND SPEED FORECAST IN THIS
ADVISORY IS BETWEEN SHIPS AND THE FSU SUPERENSEMBLE FORECAST.
 
OPHELIA CONTINUES TRAPPED BETWEEN TWO MID-LEVEL HIGH PRESSURE
AREAS...AND REMAINS NEARLY STATIONARY.  STEERING CURRENTS ARE
EXPECTED TO REMAIN WEAK FOR THE NEXT FEW DAYS...BUT LATER IN THE
FORECAST PERIOD...THE GLOBAL MODELS ARE SHOWING A BUILDING
MID-LEVEL RIDGE OVER THE UNITED STATES MID-ATLANTIC COAST.  THE
GFDL MODEL IS NO LONGER AN OUTLIER IN SHOWING OPHELIA TURNING
WESTWARD BY 4-5 DAYS...HOWEVER IT IS BY FAR THE MOST AGGRESSIVE ONE
DOING SO.  THE DYNAMICAL CONSENSUS FORECAST SHOWS A CLOCKWISE LOOP
BUT DOES NOT TAKE OPHELIA NEARLY SO FAR WEST AS THE GFDL.  SINCE
THE TRACK MODELS HAVE BEEN FLIP-FLOPPING OVER THE PAST SEVERAL
RUNS...I FEEL IT IS BEST TO TAKE A CONSERVATIVE APPROACH AND ONLY
SHOW A SLIGHT WESTWARD MOVEMENT LATE IN THE PERIOD.  WE NEED TO SEE
WHETHER SUBSEQUENT MODEL RUNS ARE MORE CONSISTENT IN SHOWING THE
WESTWARD TRACK AT THE LONGER RANGE.

THE TROPICAL STORM WARNING HAS BEEN EXTENDED A LITTLE TO THE SOUTH
ALONG THE FLORIDA EAST COAST DUE TO AN EXPENSION OF THE WIND FIELD
AND A STRENGTHENING OF THE CIRCULATION...AND NOT BECAUSE OF ANY
EXPECTED SOUTHWARD COMPONENT OF MOTION. 
 
FORECASTER PASCH
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/2100Z 28.6N  79.5W    65 KT
 12HR VT     09/0600Z 29.0N  79.2W    70 KT
 24HR VT     09/1800Z 29.5N  78.7W    70 KT
 36HR VT     10/0600Z 30.0N  78.0W    75 KT
 48HR VT     10/1800Z 30.7N  77.2W    75 KT
 72HR VT     11/1800Z 31.0N  76.0W    80 KT
 96HR VT     12/1800Z 30.0N  76.0W    80 KT
120HR VT     13/1800Z 30.0N  77.0W    80 KT
 
 
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