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Hurricane Ivan, now Category 5, has strengthened markedly over the last 24 hours and is bearing down on Jamaica where 500,000 people have been urged to evacuate from low lying areas of the Island group. On its way towards Jamaica Ivan clobbered the tiny spice island Grenada killing at least 20. The latest National Hurricane Center forecast and discussion follows.

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WTNT44 KNHC 092030

TCDAT4

HURRICANE IVAN DISCUSSION NUMBER 30

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

5 PM EDT THU SEP 09 2004

BOTH NOAA AND AIR FORCE RECONNAISSANCE PLANES HAVE BEEN IN THE EYE OF IVAN DURING THE PAST FEW HOURS. MINIMUM PRESSURE REMAINS AT ABOUT 921 MB BUT MAXIMUM FLIGHT LEVEL WINDS HAVE DECREASED TO 144 KNOTS. THIS SUGGESTS THAT INITIAL INTENSITY CAN BE LOWERED TO 130 KNOTS AT THIS TIME. THERE WERE SOME INDICATIONS FROM MICROWAVE DATA AND NOW CONFIRMED WITH THE PLANE THAT IVAN HAS A DOUBLE EYEWALL STRUCTURE. THIS MAY EXPLAIN THE RECENT SLIGHT WEAKENING. THE HURRICANE WILL PROBABLY FLUCTUATE BETWEEN CAT 4 AND 5 WHILE MOVING THROUGH AN AREA OF LOW SHEAR AND HIGH OCEANIC HEAT CONTENT BEFORE REACHING CUBA. THEREAFTER...THE EFFECTS OF LAND AND INCREASING SHEAR WILL CAUSE A GRADUAL WEAKENING.

IVAN CONTINUES TO MOVE TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 13 KNOTS. THIS GENERAL MOTION WITH A GRADUAL DECREASE IN FORWARD SPEED IS EXPECTED DURING THE NEXT 2 TO 3 DAYS. AS MENTIONED IN THE PREVIOUS DISCUSSION...THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE FORECAST BECAUSE THE HURRICANE WILL BE STEERED BY THE FLOW SURROUNDING A WELL-ESTABLISHED SUBTROPICAL RIDGE. ALL MODELS ARE HIGHLY CLUSTERED DURING THIS PERIOD...BRINGING THE HURRICANE NEAR OR OVER JAMAICA...THE CAYMAN ISLANDS AND WESTERN CUBA WITH A DECREASE IN FORWARD SPEED. THEREAFTER...THE TRACK CONTINUES TO BE UNCERTAIN SINCE STEERING CURRENTS ARE FORECAST TO WEAKEN AND MODELS DIVERGE. HOWEVER...MODELS FROM 12Z ARE IN SLIGHTLY BETTER AGREEMENT THAN IN EARLIER RUNS...AND IN GENERAL HAVE SHIFTED A LITTLE BIT WESTWARD. THE OFFICIAL FORECAST ALSO SHOWS A SLIGHT WESTWARD SHIFT.

THE WIND RADII WERE ADJUSTED BASED ON THE STEPPED FREQUENCY MICROWAVE RADIOMETER DATA ONBOARD THE NOAA P3 PLANE CURRENTLY INVESTIGATING IVAN.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/2100Z 15.0N 72.5W 130 KT
12HR VT 10/0600Z 16.1N 74.2W 130 KT
24HR VT 10/1800Z 17.5N 76.2W 135 KT
36HR VT 11/0600Z 18.8N 78.0W 130 KT
48HR VT 11/1800Z 19.7N 79.3W 140 KT
72HR VT 12/1800Z 21.5N 81.5W 140 KT
96HR VT 13/1800Z 25.0N 83.0W 115 KT
120HR VT 14/1800Z 28.0N 83.5W 100 KT

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Alastair Thompson

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Alastair Thompson is the co-founder of Scoop. He is of Scottish and Irish extraction and from Wellington, New Zealand. Alastair has 24 years experience in the media, at the Dominion, National Business Review, North & South magazine, Straight Furrow newspaper and online since 1997. He is the winner of several journalism awards for business and investigative work.

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