315 
 WTNT44 KNHC 100232
 TCDAT4
 HURRICANE IVAN DISCUSSION NUMBER  31
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 11 PM EDT THU SEP 09 2004
  
 THE LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
 INDICATED THAT THE CENTRAL PRESSURE OF IVAN WAS STILL 923 MB...BUT
 THAT THE MAXIMUM FLIGHT-LEVEL WINDS HAD DECREASED TO NEAR 130 KT. 
 BASED MAINLY ON THE PRESSURE...THE INITIAL INTENSITY REMAINS A
 POSSIBLY GENEROUS 130 KT FOR THIS PACKAGE.  THE AIRCRAFT DATA
 INDICATE THAT THE OUTER WIND MAXIMA MENTIONED IN THE PREVIOUS
 ADVISORY WAS CONTRACTING...AND THE LATEST SATELLITE IMAGERY
 SUGGESTS THAT IVAN MAY BE COMPLETING THE CURRENT CONCENTRIC EYEWALL
 CYCLE.  HOWEVER...THE AIRCRAFT DATA ALSO INDICATES ANOTHER WIND
 MAXIMA FORMING OVER THE NORTHERN SEMICIRCLE...WHICH MAY BE THE
 PRECURSOR OF THE NEXT CONCENTRIC EYEWALL CYCLE.
 
 THE INITIAL MOTION IS NOW 300/11.  THERE IS HIGH CONFIDENCE IN THE
 FIRST 36-48 HR OF THE FORECAST TRACK...AS THE SUBTROPICAL RIDGE TO
 THE NORTHEAST OF IVAN SHOULD STEER IT GENERALLY WEST-NORTHWESTWARD. 
 CONFIDENCE DIMINISHES BEYOND THAT TIME AS THE RIDGE WEAKENS DUE TO
 AN UPPER-LEVEL TROUGH OVER THE EASTERN UNITED STATES AND AN
 UPPER-LEVEL LOW OVER THE ATLANTIC CURRENTLY NEAR 31N52W.  ALL
 GUIDANCE AGREES ON A TURN TOWARD THE NORTH...WITH DIFFERENCES ON
 HOW FAR EAST THAT TURN WILL OCCUR.  THE GFS WEAKENS THE RIDGE THE
 MOST AND BRINGS IVAN NORTHWARD THROUGH THE FLORIDA PENINSULA.  THE
 UKMET AND NOGAPS KEEP MORE RIDGING NORTH OF IVAN AND THUS KEEP A
 MORE NORTH-NORTHWESTWARD MOTION.  THE NOGAPS AND GFS HAVE BOTH
 SHIFTED A LITTLE TO THE LEFT...WHILE THE GFDL HAS SHIFTED TO THE
 RIGHT.  THE OFFICIAL TRACK FORECAST IS BASICALLY AN UPDATE ON THE
 PREVIOUS PACKAGE...SHIFTING SLIGHTLY TO THE RIGHT AFTER 72 HR TO
 BRING IT IN BEST AGREEMENT WITH THE GUNS AND CONU CONSENSUS MODELS.
  
 THE INTENSITY FORECAST IS PROBLEMATIC.  THE BIGGEST CONTROLLING
 FACTOR THROUGH THE FIRST 72 HR IS LIKELY TO BE CONCENTRIC EYEWALL
 CYCLES.  THE INTENSITY FORECAST ASSUMES THAT IVAN WILL COMPLETE THE
 CURRENT CYCLE BEFORE IT REACHES JAMAICA AND THUS INTENSIFY BEFORE
 HITTING THE ISLAND.  FURTHER INTENSIFICATION IS LIKELY OVER THE
 WARM WATER BETWEEN JAMAICA AND CUBA IF THE STORM STRUCTURE REMAINS
 GOOD.  ON THE OTHER HAND...THE GFS...NOGAPS...AND SHIPS ALL
 FORECAST SIGNIFICANT SHEAR TO DEVELOP ACROSS IVAN STARTING IN ABOUT
 48 HR...WHICH COULD SLOW OR STOP DEVELOPMENT IN SPITE OF THE WARM
 WATER.  GIVEN THE CURRENT IMPRESSIVE OUTFLOW PATTERN...48 HR MIGHT
 BE TOO SOON.  THE INTENSITY FORECAST WILL DELAY THE ONSET OF
 SIGNIFICANT SHEAR UNTIL 72 HR AND HOLDS THE INTENSITY UP
 ACCORDINGLY.
  
 FORECASTER BEVEN
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      10/0300Z 15.5N  73.3W   130 KT
  12HR VT     10/1200Z 16.5N  74.8W   130 KT
  24HR VT     11/0000Z 17.7N  76.6W   135 KT
  36HR VT     11/1200Z 18.9N  78.3W   130 KT
  48HR VT     12/0000Z 19.9N  79.6W   140 KT
  72HR VT     13/0000Z 22.0N  81.5W   140 KT
  96HR VT     14/0000Z 25.5N  82.5W   120 KT
 120HR VT     15/0000Z 29.5N  83.0W    95 KT...INLAND
  
  
 $$