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 558 
 WTNT44 KNHC 080231
 TCDAT4
 HURRICANE IVAN DISCUSSION NUMBER  23
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 11 PM EDT TUE SEP 07 2004
  
 IVAN HAS CONTINUED TO STRENGTHEN DURING THE EVENING.  THE LAST PASS
 OF AN AIR FORCE RESERVE HURRICANE HUNTER THROUGH THE EYE SHOWED A
 CENTRAL PRESSURE NEAR 950 MB AND MAXIMUM FLIGHT-LEVEL WINDS OF 129
 KT AT 700 MB.  THE INITIAL INTENSITY IS SET TO 115 KT BASED ON THE
 FLIGHT-LEVEL WINDS AND SATELLITE INTENSITY ESTIMATES OF 115 KT FROM
 ALL AGENCIES.  IT SHOULD BE NOTED THAT THE SATELLITE SIGNATURE OF
 IVAN HAS IMPROVED SINCE 00Z AND THE INITIAL INTENSITY MAY BE
 CONSERVATIVE.  THE NEXT AIRCRAFT IS SCHEDULED TO ARRIVE IN IVAN
 AROUND 06Z.
 
 THE INITIAL MOTION IS 280/15.  IVAN REMAINS ON THE SOUTH SIDE OF A
 STRONG SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC.  LARGE-SCALE
 MODELS FORECAST THIS RIDGE TO SLOWLY WEAKEN AS A MID/UPPER-LEVEL
 TROUGH APPROACHES IT FROM THE NORTHWEST AND AS AN UPPER-LEVEL LOW
 DEVELOPS TO THE EAST.   WATER VAPOR IMAGERY ALSO INDICATES AN
 UPPER-LEVEL LOW OVER THE CENTRAL AND WESTERN CARIBBEAN...BUT THIS
 SEEEMS TO BE RETREATING WESTWARD AS FAST OR FASTER THAN THE
 HURRICANE.  THE SYNOPTIC PATTERN SHOULD PRODUCE A WESTWARD TO
 WEST-NORTHWESTWARD MOTION FOR THE NEXT 72 HR OR SO...FOLLOWED BY A
 MORE NORTHWESTWARD MOTION AT A SLOWER FORWARD SPEED THEREAFTER. 
 UNFORTUNATELY...MODEL GUIDANCE IS NOT VERY CONSISTENT FROM RUN TO
 RUN AT THE MOMENT.  THE GFS MADE A HUGE SHIFT TO THE RIGHT...FROM
 PASSING WEST OF FLORIDA TO PASSING 200 NM EAST OF FLORIDA.  THE
 GFDL ALSO SHIFTED TO THE RIGHT...BUT FROM A LEFT OUTLIER INTO THE
 MIDDLE OF THE GUIDANCE ENVELOPE.  THE OFFICIAL FORECAST ALSO
 SHIFTS...A LITTLE TO THE SOUTH EARLY IN THE FORECAST TO ALLOW FOR
 THE CURRENT POSITION AND MOTION AND A LITTLE TO THE RIGHT LATER IN
 THE FORECAST PERIOD.  IT IS IN BEST AGREEMENT WITH THE NOGAPS.
 
 UPPER-LEVEL WINDS ARE FORECAST TO BE GENERALLY FAVORABLE FOR
 DEVELOPMENT THROUGH THE FORECAST PERIOD...SO THE INTENSITY OF IVAN
 WILL BE MAINLY CONTROLLED BY CONCENTRIC EYEWALL CYCLES...CHANGES IN
 SEA SURFACE TEMPERATURE...AND LAND INTERACTION.  AN SSM/I OVERPASS
 AT 0105Z SHOWED AN OUTER EYEWALL STARTING TO FORM...WHICH SUGGEST
 THE CURRENT INTENSIFICATION CYCLE WILL STOP IN 6-12 HR.  HOWEVER...
 BY THAT TIME IVAN MAY BE STRONGER THAN CURRENTLY FORECAST.  THE
 HURRICANE WILL PASS OVER SOME SLIGHTLY COOLER SEA SURFACE
 TEMPERATURES THROUGH 48 HR...THEN REACH WARMER WATER NORTHWEST OF
 JAMAICA AFTER 72 HR.  REGARDLESS OF THE EXACT UPS AND DOWNS IN THE
 INTENSITY...IVAN IS EXPECTED TO REMAIN A STRONG HURRICANE THROUGH
 THE FORECAST PERIOD...MOST LIKELY CATEGORY 4 BUT POSSIBLY REACHING
 CATEGORY 5 AT SOME POINTS.
 
 HURRICANE WARNINGS HAVE BEEN ISSUED FOR ARUBA...BONAIRE...AND
 CURACAO...AS ANY MOTION SOUTH OF THE FORECAST TRACK COULD BRING
 HURRICANE FORCE WINDS NEAR OR OVER THOSE ISLANDS. 
  
 FORECASTER BEVEN
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      08/0300Z 12.1N  63.3W   115 KT
  12HR VT     08/1200Z 12.8N  65.7W   125 KT
  24HR VT     09/0000Z 13.8N  68.8W   130 KT
  36HR VT     09/1200Z 14.9N  71.6W   130 KT
  48HR VT     10/0000Z 16.3N  74.2W   130 KT
  72HR VT     11/0000Z 19.0N  78.5W   120 KT
  96HR VT     12/0000Z 21.0N  81.0W   130 KT
 120HR VT     13/0000Z 24.0N  83.0W   120 KT
  
  
 $$
 
 
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