[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 080858
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 08 2004

IVAN HAS CONTINUED TO STRENGTHEN THIS MORNING. THE MAXIMUM 700 MB
FLIGHT-LEVEL WIND REPORTED WAS 133 KT IN THE NORTHEAST QUADRANT...
WHICH EQUALS A 120-KT SURFACE WIND. THE HIGHEST WIND OBSERVED BY
DROPSONDES WAS 150 KT AT 923 MB IN THE NORTHEAST EYEWALL. THE
CENTRAL HAS ALSO BEEN AS LOW AS 947 MB...BUT THE DROPSONDE MEASURED
A SURFACE WIND OF 57 KT...SO THE CENTRAL PRESSURE WAS LIKELY LOWER.
BASED ON THIS INFORMATION...THE INTENSITY IS INCREASED TO 120 KT.

THE INITIAL MOTION IS 280/14.  IVAN HAS CONTINUED TO MOVE NORTH OF
DUE WEST ON THE SOUTH SIDE OF A STRONG SUBTROPICAL HIGH THAT IS
ORIENTED NORTHEAST-SOUTHWEST OVER THE WESTERN ATLANTIC AND INTO THE
NORTHWESTERN CARIBBEAN SEA. THE HIGH IS SEPARATING FRANCES TO THE
NORTH OVER THE SOUTHEASTERN U.S. FROM IVAN OVER THE SOUTHEASTERN
CARIBBEAN. DURING THE NEXT 2 DAYS...THE HIGH/RIDGE IS FORECAST BY
ALL THE MODELS THE GRADUALLY LIFT NORTHWARD OVER FLORIDA AND THE
EASTERN GULF OF MEXICO AS FRANCES LIFTS OUT TO THE NORTHEAST. BY
DAY 3...A STRONG MID-LEVEL TROUGH CURRENTLY OFF THE U.S. WEST COAST
IS FORECAST TO DIG INTO THE WEST COAST AND AMPLIFY THE DOWNSTREAM
RIDGE OVER THE CENTRAL U.S. AND NORTHERN MEXICO. THIS PATTERN
RESULTS IN A TROUGH CURRENTLY OVER THE NORTHERN PLAINS TO DIG
SOUTHWARD AND ERODE/WEAKEN THE RIDGE EASTWARD ACROSS THE CENTRAL
AND EASTERN GULF OF MEXICO AND FLORIDA. THE MAIN DIFFERENCE IN THE
MODELS IS HOW THEY HANDLE A YET-TO-DEVELOP MID-/UPPER-LEVEL LOW
OVER THE CENTRAL ATLANTIC. THE MAJORITY OF THE MODELS DEVELOP THE
LOW AND THEN QUICKLY WEAKEN IT AS IT MOVES WESTWARD TO THE
NORTHEAST OF THE BAHAMAS BY DAY 4. THE GFS...HOWEVER...HANGS ONTO
THE LOW LONGER AND KEEPS IT FARTHER SOUTH...WHICH ERODES THE
WESTERN PORTION OF THE RIDGE SOONER AND ALLOWS IVAN TO TURN
NORTHWARD BY 72 HOURS WHEN THE HURRICANE IS NEAR JAMAICA. FOR THE
TIME BEING...THE GFS AND THE BAM MODELS ARE CONSIDERED TO BE STRONG
EASTERN OUTLIERS AND THE OFFICIAL TRACK IS CLOSE TO THE PREVIOUS
TRACK AND A LITTLE TO THE LEFT OF THE GUNA MODEL CONSENSUS.

UPPER-LEVEL WINDS ARE FORECAST TO REMAIN FAVORABLE THROUGHOUT THE
FORECAST PERIOD. HOWEVER...TIMING CONCENTRIC EYEWALL CYCLES IS
IMPOSSIBLE...EXCEPT IN THE SHORT TERM...WHICH IVAN APPEARS TO BE
STARTING TO GO THROUGH NOW. ONCE THAT CYCLE ENDS...IVAN SHOULD
BEGIN TO INTENSIFY AGAIN AS IT MOVES AWAY FROM THE NEGATIVE
INFLUENCE OF THE NORTH COAST OF SOUTH AMERICA. INTENSITY DECREASES
AT 72HR AND 120HR REFLECT POSSIBLE PASSAGES OVER JAMAICA AND CUBA.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL      08/0900Z 12.4N  64.8W   120 KT
 12HR VT     08/1800Z 13.1N  67.2W   120 KT
 24HR VT     09/0600Z 14.2N  70.1W   125 KT
 36HR VT     09/1800Z 15.5N  72.5W   130 KT
 48HR VT     10/0600Z 16.8N  75.0W   130 KT
 72HR VT     11/0600Z 19.1N  78.7W   120 KT
 96HR VT     12/0600Z 21.5N  81.5W   130 KT
120HR VT     13/0600Z 25.0N  82.5W   120 KT


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