[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 110232
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 10 2004

DURING THE AFTERNOON...THE AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT MONITORING IVAN REPORTED A PRESSURE FALL FROM 940 MB TO
926 MB IN ABOUT 5 HOURS.  SINCE THEN...THE HURRICANE HAS CONTINUED
TO BECOME BETTER ORGANIZED...WITH SATELLITE INTENSITY ESTIMATES IN
THE 127-140 KT RANGE.  ONE CONUNDRUM IS THAT THE AIRCRAFT COULD NOT
FIND A FLIGHT-LEVEL WIND OF HIGHER THAN 123 KT...WHICH WOULD NOT
SUPPORT CATEGORY 4 INTENSITY.  THE INITIAL INTENSITY IS INCREASED
TO 135 KT BASED ON THE SATELLITE SIGNATURE...THE ESTIMATED
PRESSURE...AND THE PREMISE THAT THE WINDS ARE CATCHING UP WITH THE
PRESSURE.

THE INITIAL MOTION HAS BEEN WOBBLING AROUND 300/9.  THERE IS NO
CHANGE IN THE TRACK FORECAST PHILOSOPHY.  IVAN SHOULD MOVING
WEST-NORTHWESTWARD AROUND A WEAKENING SUBTROPICAL RIDGE...THEN
GRADUALLY TURN TOWARD THE NORTHWEST OR NORTH AFTER 48 HR AS THE
RIDGE STRENGTHENS IN THE ATLANTIC AND A TROUGH DROPS SOUTHWARD OVER
THE NORTHERN GULF COAST.  ALL GUIDANCE AGREES WITH THE BASIC
SCNEARIO...WITH THE GFS CALLING FOR AN EARLIER TURN AND LANDFALL ON
THE SOUTHWEST FLORIDA PENINSULA AND THE NOGAPS CALLING FOR A MORE
NORWARD MOTION TO THE CENTRAL FLORIDA PANHANDLE.  THE OTHER DYNAMIC
MODELS ARE IN BETWEEN...AS IS THE FORECAST TRACK...WHICH IS
BASICALLY AN UPDATE OF THE PREVIOUS TRACK AND TAKE IVAN TO THE
FLORIDA BIG BEND REGION IN 96 HR.  A SLIGHT CHANGE TO THE RIGHT OF
THE TRACK COULD BRING IVAN INLAND ANYWHERE ALONG THE WEST COAST OF
FLORIDA.

IVAN HAS WELL-DEFINED CONCENTRIC EYEWALLS SEEN IN AIRCRAFT...
MICROWAVE SATELLITE...AND EARLIER JAMAICAN RADAR DATA.  THIS
SUGGESTS THAT THE CURRENT INTENSIFICATION HAS MAYBE 6-12 HR TO
RUN...AND THAT IS NOT ALLOWING FOR ANY LAND EFFECTS AS THE SYSTEM
CROSSES JAMAICA SHORTLY.  AS THE SYSTEM CROSSES THE NORTHWESTERN
CARIBBEAN DURING THE NEXT 24-36 HR...THE UPPER-LEVEL WINDS SHOULD
REMAIN FAVORABLE ENOUGH TO ALLOW IVAN TO REGAIN CATEGORY 5 STATUS
AT SOME POINT DURING ITS FLUCTUATIONS DURING THE EYEWALL CYCLES.
AFTER 48 HR...A GRADUAL INCREASE IN SHEAR AND INTERACTION WITH LAND
SHOULD CAUSE A GRADUAL WEAKENING.  HOWEVER...IVAN SHOULD REMAIN A
MAJOR HURRICANE UNTIL LANDFALL IN FLORIDA.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      11/0300Z 17.5N  76.9W   135 KT
 12HR VT     11/1200Z 18.3N  77.9W   135 KT
 24HR VT     12/0000Z 19.3N  79.1W   140 KT
 36HR VT     12/1200Z 20.4N  80.4W   140 KT
 48HR VT     13/0000Z 21.8N  81.5W   140 KT
 72HR VT     14/0000Z 25.0N  83.0W   115 KT
 96HR VT     15/0000Z 30.0N  83.5W   100 KT...INLAND
120HR VT     16/0000Z 35.5N  83.0W    30 KT...INLAND


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