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| #44827 (Received by flhurricane at: 11:08 PM 08.Sep.2005) TCDAT1 HURRICANE OPHELIA DISCUSSION NUMBER 11 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT THU SEP 08 2005 THE LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER INDICATED THAT THE CENTRAL PRESSURE OF OPHELIA HAD RISEN TO 990 MB...WITH MAXIMUM FLIGHT LEVEL WINDS OF 74 KT. A DROPSONDE IN THE SOUTHWEST EYEWALL INDICATED 65-70 KT WINDS AT THE SURFACE...AND A SHIP JUST EAST OF THE CENTER REPORTED 60 KT WINDS. BASED ON THIS...THE INITIAL INTENSITY REMAINS 65 KT. DATA FROM THE MELBOURNE WSR-88D SHOWS THAT SINCE 21Z THE CENTER OF OPHELIA HAS LOST SOME ORGANIZATION...BECOMING BROADER AND WITH THE DOPPLER VELOCITIES DECREASING. A NOAA AIRCRAFT IS IN THE CENTER AS OF THIS WRITING AND HAS JUST REPORTED A PRESSURE OF 991 MB. WHILE THE INITIAL MOTION IS STILL NEARLY STATIONARY...THE CENTER IS JUST A LITTLE NORTHEAST OF THE PREVIOUS POSITIONS. IT IS TOO EARLY TO TELL IF THIS IS THE START OF THE EXPECTED NORTHEASTWARD DRIFT. OPHELIA IS BETWEEN TWO MID-LEVEL RIDGES...WITH THE WESTERN RIDGE WEAKENING AS A TROUGH MOVES TROUGH THE EASTERN UNITED STATES. TRACK GUIDANCE GENERALLY AGREES THAT OPHELIA WILL MOVE NORTHEASTWARD FOR 2-3 DAYS UNTIL THE TROUGH GOES BY AND THE RIDGE RE-BUILDS OVER THE EASTERN U.S.. HOWEVER...THERE ARE SIGNIFICANT DIFFERENCES IN SPEED. AFTER 72 HR...THE BUILDING RIDGE COULD CAUSE A LOOPING MOTION OFF THE SOUTHEAST U.S. COAST THROUGH 120 HR...OR EVEN MOVE THE STORM BACK TO THE COAST BEFORE 120 HR AS FORECAST BY THE GFDL AND GFDN. THE TRACK FORECAST WILL CALL FOR A SLOW NORTHEASTWARD MOTION FOR 48-72 HR...FOLLOWED BY AN EQUALLY SLOW LOOP BACK TO THE WEST...AND NOT FOLLOW THE FASTER EXTREMES OF THE GUIDANCE EITHER EAST OR WEST. THE NEW TRACK IS AN UPDATE OF THE PREVIOUS TRACK. THE INTENSITY FORECAST IS PROBLEMATIC. ON THE SIDE FAVORING STRENGTHENING...OPHELIA HAS A GOOD LOW-LEVEL STRUCTURE...IS OVER THE WARM GULF STREAM...AND IS GENERATING CONVECTIVE TOPS NEAR -80C. ON THE SIDE INHIBITING STRENGTHENING...WATER VAPOR IMAGERY INDICATES DRY AIR SURROUNDING OPHELIA...AND DATA FROM THE NOAA G4 JET SHOWS 20-30 KT OF SOUTHERLY FLOW AT 250 MB BLOWING RIGHT THROUGH THE HURRICANE. ADDITIONALLY...THE SLOW MOTION INTRODUCES THE POSSIBILITY THAT OPHELIA WILL UPWELL COLDER WATER UNDERNEATH IT IF IT MOVES OUT OF THE GULF STREAM. SHIPS AND THE GFDL BOTH CALL FOR STRENGTHENING...ALTHOUGH SHIPS MAY BE UNDERESTIMATING THE WESTERLY SHEAR NEAR THE STORM AFTER 48 HR. INDEED...MOST LARGE-SCALE MODELS SHOW AN UPPER-LEVEL TROUGH NEAR THE SOUTHEAST U.S. COAST AT 72 HR...WHICH IS AN ANOTHER COMPLICATION. GIVEN THE UNCERTAINTY...THE INTENSITY FORECAST WILL BE UNCHANGED FROM THE PREVIOUS PACKAGE...AND A SOMEWHAT LOWER INTENSITY THAN FORECAST BY SHIPS AND THE GFDL. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 09/0300Z 28.7N 79.3W 65 KT 12HR VT 09/1200Z 29.0N 79.1W 70 KT 24HR VT 10/0000Z 29.6N 78.5W 70 KT 36HR VT 10/1200Z 30.2N 77.8W 75 KT 48HR VT 11/0000Z 30.6N 77.0W 75 KT 72HR VT 12/0000Z 31.0N 76.0W 80 KT 96HR VT 13/0000Z 30.0N 76.0W 80 KT 120HR VT 14/0000Z 30.0N 77.0W 80 KT |
