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 408 
 WTNT44 KNHC 180833
 TCDAT4
 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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