Hurricane DEAN

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HURRICANE DEAN DISCUSSION NUMBER  21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042007
500 AM EDT SAT AUG 18 2007
 
NEAR 0500 UTC...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
REPORTED 154 KT FLIGHT-LEVEL WINDS IN THE NORTHERN EYEWALL OF
DEAN...AND ALSO REPORTED THAT THE CENTRAL PRESSURE FELL TO 930 MB. 
THE FLIGHT-LEVEL WINDS COULD HAVE JUSTIFIED CALLING DEAN A CATEGORY
FIVE HURRICANE.  HOWEVER...DATA FROM DROPSONDES...THE STEPPED-
FREQUENCY MICROWAVE RADIOMETER...AND SATELLITE INTENSITY ESTIMATES
DID NOT SUPPORT THAT STATUS.  THE INTENSITY WAS THUS SET TO A
SLIGHTLY MORE CONSERVATIVE 130 KT.  THERE HAS BEEN LITTLE CHANGE IN
THE SATELLITE APPEARANCE OF DEAN SINCE THE AIRCRAFT LEFT...SO 130
KT IS THE INITIAL INTENSITY FOR THIS ADVISORY.

THE INITIAL MOTION IS 275/15...AGAIN SLIGHTLY SLOWER THAN BEFORE. 
DEAN CONTINUES TO BE STEERED BY A RIDGE OVER THE WESTERN ATLANTIC
WHICH SHOULD BUILD WESTWARD DURING THE NEXT 72-96 HR AS AN
UPPER-LEVEL LOW OVER SOUTH FLORIDA MOVES WESTWARD.  IN THE SHORT
TERM...THE GUIDANCE IS IN GOOD AGREEMENT ON A WEST-NORTHWESTWARD
TRACK TOWARD JAMAICA.  THE OFFICIAL FORECAST WILL FOLLOW
THIS...WITH THE TRACK DOWN THE LEFT SIDE OF THE GUIDANCE ENVELOPE
DUE TO THE INITIAL MOTION.   AFTER THAT...UKMET...GFS...AND
CONSENSUS MODELS CALL FOR A MOTION TOWARD THE NORTHERN YUCATAN
PENINSULA AND NORTHEASTERN MEXICO.  THE GFDL CALLS FOR A MOTION
THROUGH THE YUCATAN CHANNEL TO THE TEXAS COAST...WHILE THE ECMWF
AND NOGAPS CALL FOR A MORE WESTERLY MOTION THROUGH THE CENTRAL
YUCATAN AND THE BAY OF CAMPECHE INTO MAINLAND MEXICO.  THE TRACK
FORECAST IS NUDGED A LITTLE SOUTH OF THE PREVIOUS FORECAST IN BEST
AGREEMENT WITH THE CONSENSUS MODELS.

SINCE UPPER-LEVEL WINDS ARE FORECAST TO REMAIN FAVORABLE...THE
INTENSITY FORECAST CALLS FOR A GRADUAL INCREASE IN STRENGTH THROUGH
72 HR DUE TO INCREASING SEA SURFACE TEMPERATURES AND MAXIMUM
POTENTIAL INTENSITY.  HOWEVER...THERE ARE LIKELY TO BE SIGNIFICANT
FLUCTUATIONS ON TOP OF THIS DUE TO DIFFICULT TO TIME EYEWALL
REPLACEMENT CYCLES.  PASSAGE OVER THE YUCATAN PENINSULA SHOULD
CAUSE SOME WEAKENING...FOLLOWED BY RE-INTENSIFICATION OVER THE GULF
OF MEXICO.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/0900Z 15.1N  67.3W   130 KT
 12HR VT     18/1800Z 15.6N  69.6W   130 KT
 24HR VT     19/0600Z 16.5N  72.8W   135 KT
 36HR VT     19/1800Z 17.6N  76.4W   135 KT
 48HR VT     20/0600Z 18.5N  80.0W   135 KT
 72HR VT     21/0600Z 20.5N  86.5W   140 KT
 96HR VT     22/0600Z 22.5N  92.5W   110 KT
120HR VT     23/0600Z 24.5N  98.0W   115 KT...INLAND
 
$$
FORECASTER BEVEN
 
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