[Tropical] Tropical Cyclone Discussion

[Nashville EMWIN]

WTNT44 KNHC 081448
TCDAT4
HURRICANE IVAN DISCUSSION NUMBER  25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED SEP 08 2004

LAST FIX FROM A RECONNAISSANCE PLANE EARLIER THIS MORNING INDICATED
THAT THE PRESSURE INCREASED TO 955 MB BUT FLIGHT-LEVEL WINDS WERE
STILL 133 KNOTS IN THE NORTHERN EYEWALL. SINCE THEN...HIGH
RESOLUTION VISIBLE SATELLITE IMAGES REVEAL THAT THE EYE IS NOT AS
DISTINCT AS EARLIER BUT STILL VISIBLE. INITIAL INTENSITY REMAINS AT
120 KNOTS. BECAUSE THE HURRICANE WILL HAVE TO FIGHT SOME SHEAR AND
WILL BE MOVING JUST NORTH OF THE SOUTH AMERICAN COAST...THERE MAY
BE SOME WEAKENING DURING THE NEXT 12 TO 24 HOURS. THEREAFTER...THE
HURRICANE WILL BE OVER THE NORTHWESTERN CARIBBEAN SEA WHERE THERE
IS HIGH OCEANIC HEAT CONTENT AND LOWER SHEAR. SO...IVAN IS EXPECTED
TO INTENSIFY BEFORE REACHING CUBA. NEVERTHERELESS...THESE ARE
BASICALLY FLUCTUATIONS IN INTENSITY AND THE BOTTOM LINE IS THAT
IVAN IS EXPECTED TO REMAIN A VERY DANGEROUS HURRICANE.

SATELLITE AND EARLIER RECONNAISSANCE FIXES INDICATE THAT IVAN IS
MOVING TOWARD THE WEST-NORTHWEST OR 285 DEGREES AT 14 KNOTS. DURING
THE NEXT 24 TO 48 HOURS...THE SUBTROPICAL RIDGE TO THE NORTH OF
IVAN IS EXPECTED TO CHANGE LITTLE...FORCING IVAN TO MOVE TOWARD THE
WEST-NORTHWEST. THEREAFTER...THE RIDGE IS FORECAST TO WEAKEN AND A
BROAD MID-LEVEL TROUGH WILL LIKELY BECOME ESTABLISHED OVER THE GULF
OF MEXICO. THIS PATTERN SHOULD MOVE THE HURRICANE ON A NORTHWEST
AND NORTH-NORTHWEST TRACK WITH A DECREASE IN FORWARD SPEED. IT MUST
BE EMPHASIZED THAT THE FORECAST TRACK BEYOND 72 HOURS IS HIGHLY
UNCERTAIN SINCE STEERING CURRENTS WILL BE WEAK AND ARE CURRENTLY
NOT WELL-DEFINED IN THE FORECAST MODELS. IN FACT...SOME RELIABLE
MODELS BRING IVAN OVER FLORIDA AND ANOTHER RELIABLE GROUP MOVE THE
HURRICANE TOWARD THE GULF OF MEXICO. THERE IS NO APPARENT REASON TO
FAVOR ONE SCENARIO OVER THE OTHER AT THIS TIME. THEREFORE...THE
OFFICIAL FORECAST REMAINS NEAR THE GLOBAL MODEL CONSENSUS AND
PRESUMES THAT THERE WILL BE ENOUGH RIDGING TO KEEP THE HURRICANE ON
A NORTHWEST TO NORTH-NORTHWEST TRACK... BRINGING DANGEROUS IVAN
OVER WESTERN CUBA IN 4 DAYS AND INTO THE EASTERN GULF OF MEXICO BY
DAY FIVE.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL      08/1500Z 12.7N  66.2W   120 KT
 12HR VT     09/0000Z 13.3N  68.3W   115 KT
 24HR VT     09/1200Z 14.5N  71.0W   120 KT
 36HR VT     10/0000Z 16.0N  73.5W   125 KT
 48HR VT     10/1200Z 17.5N  76.0W   125 KT NEAR JAMAICA
 72HR VT     11/1200Z 19.5N  79.0W   125 KT
 96HR VT     12/1200Z 22.5N  82.0W   125 KT  OVER WESTERN CUBA
120HR VT     13/1200Z 26.0N  84.0W   115 KT


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