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Hurricane DEAN


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HURRICANE DEAN DISCUSSION NUMBER  37
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 AM EDT WED AUG 22 2007
 
REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT THE CENTRAL CORE OF DEAN COLLAPSED DURING PASSAGE ACROSS THE
YUCATAN PENINSULA.  THE AIRCRAFT FOUND THE RADIUS OF MAXIMUM WINDS
HAD EXPANDED TO 55 N MI IN ASSOCIATION WITH A LARGE CONVECTIVE
BAND.  SATELLITE IMAGERY SHOWS CONVECTION FORMING CLOSE TO THE
CIRCULATION CENTER...BUT THIS DOES NOT CORRESPOND WITH ANY WIND
MAXIMUM SEEN BY THE AIRCRAFT.  THE MINIMUM CENTRAL PRESSURE WAS 979
MB AND THE MAXIMUM SURFACE WINDS FROM THE STEPPED FREQUENCY
MICROWAVE RADIOMETER WERE 64 KT.  BASED ON THIS AND THE POSSIBILITY
THE MAXIMUM WINDS WERE NOT SAMPLED...THE INITIAL INTENSITY REMAINS
70 KT.
 
THE INITIAL MOTION IS 285/17.  A DEEP-LAYER RIDGE NORTH AND
NORTHEAST OF DEAN SHOULD STEER THE CYCLONE GENERALLY
WEST-NORTHWESTWARD UNTIL LANDFALL IN ABOUT 12 HR...AND UNTIL
EVENTUAL DISSIPATION OVER THE MOUNTAINS OF MEXICO.
 
UPPER-LEVEL WINDS HAVE BECOME SOMEWHAT LESS FAVORABLE FOR
INTENSIFICATION...WITH THE SHIPS MODEL AND ANALYSES FROM CIMSS AT
THE UNIVERSITY OF WISCONSIN SHOWING 15-20 KT OF NORTHEASTERLY
VERTICAL WIND SHEAR.  THIS...COMBINED WITH THE LARGE CORE
SIZE...SUGGESTS THAT RE-INTENSIFICATION MAY BE SLOWER THAN
PREVIOUSLY THOUGHT.  THE INTENSITY FORECAST NOW CALLS FOR WINDS TO
INCREASE TO 80 KT BEFORE LANDFALL...WHICH IS A LITTLE ABOVE MOST OF
THE GUIDANCE.  DEAN SHOULD WEAKEN AFTER LANDFALL AND DISSIPATE BY
48 HR AT THE LATEST.
 
THE WIND RADII HAVE BEEN CHANGED SIGNIFICANTLY BASED ON AIRCRAFT...
BUOY...AND QUIKSCAT OBSERVATIONS.  THE INCREASED AREA OF HURRICANE
FORCE WINDS HAS REQUIRED A NORTHWARD EXTENSION OF THE HURRICANE
WARNING ALONG THE MEXICAN COAST. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      22/0900Z 20.3N  94.8W    70 KT
 12HR VT     22/1800Z 20.9N  97.1W    80 KT
 24HR VT     23/0600Z 21.4N 100.2W    40 KT...INLAND
 36HR VT     23/1800Z 21.8N 103.5W    20 KT...INLAND
 48HR VT     24/0600Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
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