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| #44774 (Received by flhurricane at: 4:46 PM 08.Sep.2005) TCDAT1 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 |
