[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 050232
TCDAT4
TROPICAL STORM IVAN DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SAT SEP 04 2004

IVAN CONTINUES TO BECOME BETTER ORGANIZED...WITH A CURVED COLD
CONVECTIVE BAND TO THE EAST OF A WARM SPOT THAT IS NOT YET
DESERVING OF BEING CALLED AN EYE.  SATELLITE INTENSITY ESTIMATES
ARE 77 KT FROM AFWA AND 65 KT FROM TAFB AND SAB.  HOWEVER...AN
SSM/I OVERPASS AT 0005Z DID NOT SHOW AN EYE OR EVEN THAT GOOD OF
CONVECTIVE BANDING.  THEREFORE...THE SYSTEM WILL REMAIN A TROPICAL
STORM AT THIS TIME WITH AN INITIAL INTENSITY OF 60 KT.

THE INITIAL MOTION IS 275/16.  IVAN REMAINS ON THE SOUTH SIDE OF A
STRONG SUBTROPICAL RIDGE...AND THIS SHOULD LIKELY CONTINUE FOR THE
NEXT 3-4 DAYS.  BY DAY 5...THE CYCLONE WILL BE NEARING A FORECAST
WEAKNESS IN THE RIDGE.  THIS PATTERN SHOULD ALLOW A GENERALLY WEST-
NORTHWESTWARD MOTION FOR THE NEXT 3-4 DAYS...FOLLOWED BY A GRADUAL
MORE NORTHERLY TURN.  TRACK GUIDANCE IS UNUSUALLY WELL CLUSTERED
EVEN OUT TO DAY FIVE...CALLING FOR IVAN TO MOVE WEST-NORTHWESTWARD
THROUGH THE CENTRAL LESSER ANTILLES IN ABOUT 72 HR AND THEN PASS
OVER HISPANIOLA BETWEEN 96-120 HR.  THE NEW FORECAST TRACK FOLLOWS
THE MIDDLE OF THIS GUIDANCE SUITE AND IS BASICALLY AN UPDATE OF THE
PREVIOUS PACKAGE.

LARGE-SCALE GUIDANCE PREDICTS LIGHT VERTICAL SHEAR FOR THE NEXT 3-4
DAYS...SO THERE IS NO OBVIOUS REASON WHY IVAN SHOULD NOT GRADUALLY
INTENSIFY.  THE INTENSITY FORECAST FOLLOWS THIS PHILOSOPHY.  WITH
THE FORECAST TRACK TAKING THE STORM OVER HISPANIOLA BETWEEN 96-120
HR...THE FORECAST INTENSITY IS CONSIDERABLY REDUCED.  THERE IS ALSO
SOME UNCERTAINTY OF WHETHER THE SHEAR WILL REMAIN FAVORABLE AFTER
96 HR...AS THE GFS AND NOGAPS DEVELOP AN UPPER-LEVEL TROUGH OVER
THE BAHAMAS BY 120 HR.

AS NOTED EARLIER...BECAUSE OF THE TYPICAL TRACK FORECAST ERRORS AT 5
DAYS...THE CENTER COULD EASILY PASS SOUTH...OR NORTH...OF THE
ISLAND OF HISPANIOLA.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      05/0300Z  9.4N  42.2W    60 KT
 12HR VT     05/1200Z  9.8N  44.7W    65 KT
 24HR VT     06/0000Z 10.7N  48.2W    70 KT
 36HR VT     06/1200Z 11.8N  51.5W    75 KT
 48HR VT     07/0000Z 12.7N  55.1W    80 KT
 72HR VT     08/0000Z 14.5N  61.5W    90 KT
 96HR VT     09/0000Z 16.5N  67.0W   100 KT
120HR VT     10/0000Z 20.0N  72.0W    65 KT


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