[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 090853
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT THU SEP 09 2004

AIR FORCE RECON THIS MORNING HAS FOUND AN INTENSE HURRICANE IVAN.
THE CENTRAL PRESSURE OF 922 MB HAS DROPPED 15 MB IN THE PAST 7
HOURS...WHILE THE 700 MB FLIGHT-LEVEL WINDS HAVE INCREASED TO 154
KT...EQUAL TO 139 KT SURFACE WIND...TO THE NORTH AND NORTHEAST OF
THE CENTER ON TWO SEPARATE PASSES. IN ADDITION...AND EYEWALL
DROPSONDE RECORDED A WIND SPEED OF 175 KT AT ABOUT 630 FT ABOVE SEA
LEVEL. BASED ON THIS INFORMATION...IVAN IS EASILY UPGRADED TO A
140-KT CATEGORY 5 HURRICANE. AS I WRITE...A NEW RECON REPORT
INDICATES AN EXTRAPOLATED PRESSURE OF 916 MB.

THE INITIAL MOTION IS 290/13. IVAN HAS BEEN SLOWLY GAINING LATITUDE
OVER THE PAST 24 HOURS...AND THE LAST TWO RECON FIX POSITIONS
SUGGEST THAT IVAN MAY BE MOVING AT 295 DEGREES. DROPSONDE DATA FROM
THE 00Z SYNOPTIC SURVEILLANCE FLIGHTS AROUND IVAN HAS RESULTED IN
TIGHT AGREEMENT AMONG ALL OF THE AVAILABLE NHC MODELS THROUGH 60
HOURS...ON IVAN MOVING OVER OR AT LEAST VERY NEAR JAMAICA IN 36-48
HOURS. AFTER THAT...THE MODELS DIVERGE CONSIDERABLY...ALTHOUGH THE
SPREAD IS MUCH LESS THAN IT HAS BEEN OVER THE PREVIOUS 2-3 DAYS.
UNFORTUNATELY...THE MODEL SPREAD STILL BRACKETS THE FLORIDA
PENINSULA. THE MAIN DIFFERENCE BETWEEN THE MODELS AGAIN REMAINS IN
HOW THEY HANDLE THE DEVELOPMENT AND FUTURE TRACK OF A MID- TO
UPPER-LEVEL LOW CURRENTLY NEAR 34N 48W. WATER VAPOR WINDS SUGGEST
THAT THE UPPER-LOW IS STRONGER THAN ALL OF THE MODELS HAVE BEEN
FORECASTING. HOWEVER...THE MODEL THAT INITIALIZED THE LOW THE BEST
AT 00Z WAS NOGAPS. THIS MODEL HAS BEEN VERY CONSISTENT...ALONG WITH
THE ECMWF MODEL...ON BRINGING IVAN ACROSS WEST-CENTRAL CUBA AND
THEN OVER OR NEAR THE FLORIDA PENINSULA. THE UKMET MODEL REMAINS
THE WESTERNMOST OUTLIER...WHILE THE GFS IS STILL THE EASTERNMOST
OUTLIER. HOWEVER...BOTH MODELS HAVE BEEN GRADUALLY SHIFTING THEIR
TRACKS TOWARD FLORIDA...AND THE LATEST GFDL RUN NOW TAKES IVAN
ACROSS SOUTHEAST FLORIDA IN 96-120 HOURS. GIVEN THE BETTER
AGREEMENT AMONG THE MODELS ON THIS FORECAST CYCLE...THE OFFICIAL
TRACK IS CLOSE TO THE PREVIOUS FORECAST THROUGH 72 HOURS...AND THEN
SHIFTED SLIGHTLY EASTWARD AT 96- AND 120-HR.

THE UPPER-LEVEL OUTFLOW PATTERN IS IMPRESSIVE AND WELL-ESTABLISHED
...AND IF ANYTHING...WILL ONLY GET BETTER FOR THE NEXT 72-96 HOURS.
THEREFORE...THE FUTURE INTENSITY WILL LIKELY BE MODULATED BY INNER-
CORE CONVECTIVE CHANGES AND LAND INTERACTION SINCE TH WATER AHEAD OF
IVAN IS ONLY FORECAST TO GET WARMER...AS WARM AS 30C SOUTH OF CUBA
AND OVER THE FLORIDA STRAITS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      09/0900Z 13.9N  70.0W   140 KT
 12HR VT     09/1800Z 14.8N  72.0W   140 KT
 24HR VT     10/0600Z 16.2N  74.3W   135 KT
 36HR VT     10/1800Z 17.6N  76.4W   135 KT
 48HR VT     11/0600Z 19.1N  78.3W   125 KT
 72HR VT     12/0600Z 21.0N  80.2W   125 KT
 96HR VT     13/0600Z 24.0N  81.0W   115 KT
120HR VT     14/0600Z 28.0N  81.0W    80 KT...INLAND OVER FLORIDA


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