[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 070900
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 07 2004

AIR FORCE RECON INDICATES THAT IVAN HAS AND IS BECOMING BETTER
ORGANIZED...WHICH IS ALSO SUPPORTED BY THE DRASTICALLY IMPROVED
APPEARANCE IN SATELLITE IMAGERY. RECON REPORTS INDICATE AN INNER
CONCENTRIC EYEWALL HAS ALMOST COMPLETELY DECAYED WHILE A NEW OUTER
EYEWALL HAS STABILIZED AT AROUND 20 NMI DIAMETER. THE HIGHEST 700
MB FLIGHT-LEVEL WIND REPORTED SO FAR HAS BEEN 107 KT IN THE
NORTHWEST QUADRANT. A DROPSONDE IN THE SAME AREA INDICATED 137 KT
WINDS AT 953 MB...BUT THIS IS BELIEVED TO BE A WIND GUST. HOWEVER
...THE OVERALL VERTICAL WIND PROFILE CLEARLY REVEALED THAT IVAN IS
IS BECOMING MUCH BETTER ORGANIZED AS COMPARED TO JUST 6 HOURS AGO.

THE INITIAL MOTION IS 280/16.  RECONNAISSANCE AND SATELLITE POSITION
ESTIMATES INDICATE THAT IVAN HAS SLOWED ITS FORWARD SPEED SOMEWHAT.
A NOAA GULFSTREAM-IV JET PERFORMED A SURVEILLANCE FLIGHT AROUND THE
PERIPHERY OF IVAN LATE YESTERDAY EVENING WHICH HAD A SIGNIFICANT
IMPACT ON THE 00Z MODEL RUNS. MOST OF THE NHC MODEL GUIDANCE IS
TIGHTLY CLUSTERED ABOUT A WEST-NORTHWESTWARD MOTION WITH A GRADUAL
DECREASE IN FORWARD SPEED THROUGH 72 HOURS AS IVAN MOVES AROUND THE
SOUTHWEST PERIPHERY OF THE STRONG SUBTROPICAL RIDGE TO THE NORTH OF
THE CARIBBEAN ISLANDS. HOWEVER...AFTER THAT THE MODELS BEGIN TO
DIVERGE ENOUGH FOR ALREADY STORM WEARY PEOPLE IN FLORIDA TO BE
CONCERNED ABOUT. THE GFDL HAS BEEN VERY CONSISTENT WITH A TRACK
BETWEEN HAITI AND JAMAICA AND ACROSS SOUTHEASTERN CUBA. THE NEW 00Z
GFS RUN NOW HAS A MORE REALISTIC TROPICAL CYCLONE VORTEX IN THE
MODEL INITIALIZATION...AND IT HAS SHIFTED ITS TRACK MORE TO THE
EAST OR RIGHT OF THE PREVIOUS RUNS. THIS IS ALSO CONSISTENT WITH
THE LATEST NOGAPS AND GFDN MODELS. THE UKMET APPEARS TO BE THE ONLY
OUTLIER AT 96HR AND 120HR BY TAKING IVAN WEST-NORTHWESTWARD TOWARD
WESTERN CUBA. THIS SEEMS UNLIKELY GIVEN THAT ALL OF THE MODELS ...
INCLUDING THE UKMET...GRADUALLY BUILD A STRONG HIGH AMPLITUDE
HIGH/RIDGE ACROSS THE CENTRAL U.S. AND MEXICO AND INTO THE WESTERN
GULF OF MEXICO BY 120 HOURS THAT SHOULD ACT TO BLOCK ANY WESTWARD
MOTION INTO THE CENTRAL AND WESTERN GULF. IN RESPONSE TO THE
WESTERN U.S. RIDGING ...A BROAD TROUGH IS FORECAST TO REMAIN IN THE
WAKE OF FRANCES ACROSS THE SOUTHEASTERN U.S. AND THE CENTRAL AND
EASTERN GULF OF MEXICO...WHICH UNFORTUNATELY OPENS THE DOOR FOR
IVAN TO POSSIBLY SLOW AND MOVE MORE NORTHWARD BY 120HR ACROSS
CENTRAL CUBA. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE PREVIOUS
TRACK THROUGH 72 HOURS...AND THEN TO THE RIGHT OF TRACK AFTER THAT
...WHICH IS CONSISTENT WITH THE GUNA AND GUNS CONSENSUS MODELS.

IVAN IS FORECAST TO MOVE OVER PROGRESSIVELY WARMER WATER...REACHING
NEAR 30C WATER IN 72HR. GIVE THE CURRENT AND FORECAST OUTFLOW
PATTERN TO REMAIN QUITE IMPRESSIVE...THEN AT LEAST STEADY
INTENSIFICATION APPEARS TO BE IN ORDER. IF THE OUTFLOW ON THE WEST
SIDE OF IVAN TAPS INTO THE MID-/UPPER-LEVEL LOW TO THE WEST OVER
THE CENTRAL CARIBBEAN SEA...THEN RAPID INTENSIFICATION COULD OCCUR.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      07/0900Z 11.4N  58.5W    95 KT
 12HR VT     07/1800Z 12.0N  61.2W   105 KT
 24HR VT     08/0600Z 13.0N  64.5W   110 KT
 36HR VT     08/1800Z 14.2N  67.6W   115 KT
 48HR VT     09/0600Z 15.5N  70.5W   120 KT
 72HR VT     10/0600Z 18.0N  75.5W   120 KT
 96HR VT     11/0600Z 20.5N  79.0W   120 KT
120HR VT     12/0600Z 23.0N  81.0W   100 KT...INLAND


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