[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 112035
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  38
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT SEP 11 2004

THERE HAVE BEEN SOME GRADUAL CHANGES IN THE STEERING PATTERN OVER
THE LAST DAY OR SO WHICH COULD RESULT IN THE HURRICANE MOVING ON A
TRACK NOT AS CLOSE TO SOUTH FLORIDA.  WHILE THIS MAY BE GOOD NEWS
FOR SOUTH FLORIDA...IT IS NOT SO FOR OTHER REGIONS OF THE EASTERN
GULF COAST. WATER VAPOR IMAGES SHOW THAT A RIDGE OF HIGH PRESSURE
AT THE MID TO UPPER-LEVELS HAS DEVELOPED FROM THE GULF OF MEXICO
EASTWARD ACROSS FLORIDA. IT APPEARS THAT THIS RIDGE HAS BEEN
FORCING THE HURRICANE ON A MORE WESTWARD TRACK...DELAYING THE
EXPECTED NORTHWEST AND NORTHWARD TURN. ALTHOUGH THE NORTHWARD TURN
IS STILL FORECAST TO OCCUR AS A WEAKNESS DEVELOPS IN THE GULF OF
MEXICO...IT IS NOW EXPECTED TO OCCUR OVER EXTREME WESTERN CUBA AND
OVER THE OPEN WATERS OF THE GULF OF MEXICO. THIS TRACK INCREASES
THE HURRICANE RISK FOR THE NORTHEASTERN GULF OF MEXICO REGION AND
DECREASES IT FOR SOUTH FLORIDA. THE WESTWARD SHIFT OF THE OFFICIAL
FORECAST REMAINS IN AGREEMENT WITH GUIDANCE WHICH HAS ALSO BEEN
SHIFTING GRADUALLY WESTWARD.

AS WAS THOUGHT POSSIBLE...IVAN HAS REGAINED CATEGORY FIVE STRENGTH.
A RECONNAISSANCE PLANE JUST MEASURED 161 KNOTS AT 700 MB AND AN
EXTRAPOLATED PRESSURE OF 914 MB. THE DROP MEASURED 918 MB BUT IT
HAD 29 KNOTS AT THE SURFACE. INITIAL INTENSITY HAS BEEN INCREASED
TO 145 KNOTS. THERE ARE NO SKILLS IN PREDICTING CHANGES IN
INTENSITY WITH SUCH EXTREMELY INTENSE HURRICANES...SO IVAN IS KEPT
AT 145 KNOTS UNTIL LANDFALL IN CUBA. THEREAFTER...THE SHEAR IS
FORECAST TO INCREASE...SO A GRADUAL WEAKENING IS INDICATED.
NEVERTHERLESS... IVAN IS EXPECTED TO REACH THE UNITES STATES AS A
MAJOR HURRICANE.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL      11/2100Z 18.2N  79.3W   145 KT
 12HR VT     12/0600Z 18.7N  80.5W   145 KT
 24HR VT     12/1800Z 20.0N  82.0W   145 KT
 36HR VT     13/0600Z 21.5N  83.1W   145 KT...NEARING CUBA
 48HR VT     13/1800Z 23.1N  84.0W   130 KT
 72HR VT     14/1800Z 26.5N  85.0W   115 KT
 96HR VT     15/1800Z 31.0N  85.0W    60 KT...INLAND
120HR VT     16/1800Z 36.0N  83.0W    25 KT...INLAND


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