Hurricane DEAN

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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
 
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