[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 050837
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 05 2004

INFRARED SATELLITE IMAGERY AND A 0450Z TRMM OVERPASS SHOW THAT IVAN
HAS DEVELOPED SUFFICIENT ORGANIZED CONVECTION AROUND THE WARM SPOT
SEEN EARLIER TO NOW CALL IT AN EYE.  SATELLITE INTENSITY ESTIMATES
ARE 77 KT FROM AFWA AND 65 KT FROM TAFB AND SAB.  THUS...IVAN IS
UPGRADED TO A 65 KT HURRICANE.

THE INITIAL MOTION IS NOW 280/18...AND THE SHORT-TERM MOTION MAY BE
EVEN FASTER.  IVAN IS ON THE SOUTH SIDE OF A STRONG SUBTROPICAL
RIDGE...AND THIS SHOULD LIKELY CONTINUE FOR THE NEXT 3-4 DAYS.
THIS PATTERN SHOULD ALLOW A GENERALLY WEST-NORTHWESTWARD MOTION FOR
THE NEXT 3-4 DAYS...A SCENARIO SUPPORTED BY WELL-CLUSTERED TRACK
GUIDANCE.  THE GUIDANCE REMAINS FAIRLY WELL-CLUSTERED AROUND A
WEST-NORTHWEST MOTION ON DAY 5...BUT BY THAT TIME THERE ARE
SIGNIFICANT DISAGREEMENTS ON THE SYNOPTIC PATTERNS OVER THE WESTERN
ATLANTIC RANGING FROM THE NOGAPS SOLID-LOOKING RIDGE TO THE GFS
BROAD POST-FRANCES TROUGH.  THE 120 HR POINT WILL CONTINUE A
WEST-NORTHWEST MOTION...BUT THE CONFIDENCE IN THIS POINT HAS
DECREASED.  THE NEW FORECAST TRACK IS NUDGED A LITTLE TO THE SOUTH
OF THE PREVIOUS PACKAGE BASED MAINLY ON THE INITIAL POSITION.

LARGE-SCALE GUIDANCE PREDICTS LIGHT VERTICAL SHEAR FOR THE NEXT 3-4
DAYS...SO THERE IS NO OBVIOUS REASON WHY IVAN SHOULD NOT INTENSIFY
FURTHER.  THE INTENSITY FORECAST FOLLOWS THIS PHILOSOPHY...AND IT
IS POSSIBLE THERE COULD BE RAPID STRENGTHENING.  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 IN PARTICULAR SHOWS THE UPPER-LEVEL WINDS
BECOMING LESS FAVORABLE.

AS NOTED EARLIER...BECAUSE OF THE TYPICAL TRACK FORECAST ERRORS AT
4-5 DAYS...THE CENTER COULD EASILY PASS SOUTH...OR NORTH...OF THE
ISLAND OF HISPANIOLA.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL      05/0900Z  9.7N  44.3W    65 KT
 12HR VT     05/1800Z 10.3N  47.1W    70 KT
 24HR VT     06/0600Z 11.3N  50.6W    75 KT
 36HR VT     06/1800Z 12.2N  54.1W    80 KT
 48HR VT     07/0600Z 13.1N  57.5W    85 KT
 72HR VT     08/0600Z 14.5N  63.5W    95 KT
 96HR VT     09/0600Z 17.0N  69.0W   105 KT
120HR VT     10/0600Z 20.5N  73.5W    70 KT


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