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| #147064 (Received by flhurricane at: 4:52 AM 20.Aug.2007) TCDAT4 HURRICANE DEAN DISCUSSION NUMBER 29 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042007 500 AM EDT MON AUG 20 2007 OBSERVATIONS FROM THE LAST AIR FORCE HURRICANE HUNTER MISSION AGAIN INDICATED A CONCENTRIC EYEWALL STRUCTURE. THE PEAK FLIGHT-LEVEL WIND SPEED WAS 145 KT WITH AN SFMR SURFACE WIND MEASUREMENT OF 125 KT IN THE NORTHEAST QUADRANT. A GPS DROPSONDE MEASURED A SURFACE WIND SPEED OF 133 KT IN THE SAME QUADRANT...BUT BASED ON LOWER-LAYER AVERAGES FROM THE SONDE...THIS PROBABLY DOES NOT QUITE CORRESPOND TO A 1-MINUTE AVERAGE SURFACE WIND. BASED ON ALL OF THESE DATA THE CURRENT INTENSITY IS SET AT 130 KT. DEAN IS MOVING OVER WATERS OF EXTREMELY HIGH OCEANIC HEAT CONTENT WITH WEAK SHEAR AND EXHIBITS A CLASSIC UPPER-TROPOSPHERIC OUTFLOW PATTERN. DEAN CERTAINLY HAS THE POTENTIAL TO STRENGTHEN INTO A CATEGORY FIVE HURRICANE WITHIN THE NEXT 24 HOURS AND THIS IS REFLECTED IN THE OFFICIAL FORECAST. WEAKENING WILL OCCUR DUE TO THE TRANSIT OVER THE YUCATAN PENINSULA AND THE OFFICIAL FORECAST ROUGHLY FOLLOWS THE INLAND DECAY SHIPS MODEL. DEAN IS FORECAST TO RESTRENGTHEN OVER THE BAY OF CAMPECHE...AND THE GFDL AND HWRF GUIDANCE SUGGEST THAT IT COULD REGAIN MAJOR HURRICANE STATUS BEFORE MAKING ITS FINAL LANDFALL. THIS IS NOT EXPLICITLY SHOWN IN THE OFFICIAL FORECAST BUT ADDITIONAL STRENGTHENING WILL LIKELY OCCUR BETWEEN THE 48-HOUR FORECAST AND LANDFALL. AIRCRAFT AND SATELLITE FIXES OVER THE PAST SIX HOURS OR SO GIVE ESSENTIALLY A DUE WESTWARD MOTION AT A SLIGHTLY FASTER FORWARD SPEED...270/18. AS A MID- TO UPPER-TROPOSPHERIC CYCLONE CONTINUES MOVING WESTWARD OVER THE WESTERN GULF OF MEXICO...THE FLOW TO THE SOUTH OF A STRENGTHENING DEEP-LAYER HIGH PRESSURE SYSTEM OVER THE SOUTHEASTERN U.S. WILL BE THE DOMINANT STEERING MECHANISM FOR DEAN. THEREFORE...A WESTWARD TO WEST-NORTHWESTWARD MOTION IS LIKELY FOR THE NEXT COUPLE OF DAYS. THE OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND IS QUITE CLOSE TO THE GFDL...U.K. MET...NOGAPS...AND GFS CONSENSUS AND FSU SUPERENSEMBLE TRACKS. FORECAST POSITIONS AND MAX WINDS INITIAL 20/0900Z 17.7N 80.7W 130 KT 12HR VT 20/1800Z 18.1N 83.5W 135 KT 24HR VT 21/0600Z 18.8N 87.0W 140 KT 36HR VT 21/1800Z 19.6N 90.5W 75 KT...INLAND 48HR VT 22/0600Z 20.5N 94.0W 90 KT...BAY OF CAMPECHE 72HR VT 23/0600Z 22.0N 100.5W 30 KT...INLAND 96HR VT 24/0600Z...DISSIPATED $$ FORECASTER PASCH/BROWN |
