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HURRICANE IRIS DISCUSSION NUMBER 11
NATIONAL WEATHER SERVICE MIAMI FL
5 AM EDT SUN OCT 07 2001
AFTER MOVING MOSTLY WESTWARD...EVEN WOBBLING A LITTLE SOUTH OF
WEST...THE HURRICANE APPEARS TO HAVE RESUMED A WEST-NORTHWEST MOTION
OF ABOUT 285/15. GLOBAL MODELS MAINTAIN A RIDGE TO THE NORTH OF THE
IRIS DURING THE FORECAST PERIOD...AND THIS RIDGE IS PREDICTED TO
STRENGTHEN A BIT OVER THE EASTERN GULF OF MEXICO IN A COUPLE OF
DAYS. BECAUSE OF THE MORE WESTWARD MOTION OVER THE PAST
6-12 HOURS...THE OFFICIAL FORECAST TRACK HAS BEEN ADJUSTED JUST
SLIGHTLY TO THE SOUTH OF THE PREVIOUS ONE. THIS IS ROUGHLY IN THE
MIDDLE OF THE NUMERICAL GUIDANCE SUITE WHICH IS FAIRLY TIGHTLY
CLUSTERED. THE AVN MODEL IS SOMEWHAT TO THE NORTH OF THE OFFICIAL
FORECAST...HOWEVER THAT MODEL HAS EXHIBITED A SLIGHT NORTHWARD BIAS
FOR IRIS THUS FAR.
ALTHOUGH THE SATELLITE PRESENTATION HAS BEEN RATHER
RAGGED-LOOKING...LATEST AERIAL RECONNAISSANCE OBSERVATIONS SUGGEST
THAT IRIS IS MAINTAINING ITS STRENGTH. THE EYE WALL IS STILL CLOSED
AND...EVEN THOUGH THE HIGHEST FLIGHT LEVEL WINDS SO FAR ON THIS
MISSION WERE 76 KNOTS...THE CENTRAL PRESSURE READING WAS DOWN TO 987
MILLIBARS. RECENTLY...A GPS DROPSONDE SHOWED A SPOT SURFACE WIND
SPEED OF 70 KNOTS JUST NORTH OF THE CENTER. IT IS PRESUMED THAT
SLIGHTLY STRONGER SURFACE WINDS EXIST SOMEWHERE OVER THE NORTHERN
SEMICIRCLE OF THE HURRICANE. AN UPPER-LEVEL CYCLONE HAS BEEN
ROTATING AROUND THE SOUTHERN SEMICIRCLE OF IRIS...AND PERHAPS
INTERFERING WITH THE OUTFLOW. THAT LOW IS NOW SOUTHEAST OF THE
HURRICANE...AND APPEARS TO BE INCREASING ITS SEPARATION FROM IRIS.
WE ANTICIPATE THAT THE ENVIRONMENT WILL BECOME MORE FAVORABLE FOR
INTENSIFICATION AS THE HURRICANE ENTERS THE NORTHWEST CARIBBEAN SEA.
THE SHIPS MODEL BRINGS IRIS TO MAJOR HURRICANE STATUS IN 48 HOURS...
AND THE OFFICIAL FORECAST IS JUST SLIGHTLY MORE CONSERVATIVE.
FORECASTER PASCH
FORECAST POSITIONS AND MAX WINDS
INITIAL 07/0900Z 17.1N 76.1W 75 KTS
12HR VT 07/1800Z 17.7N 78.0W 80 KTS
24HR VT 08/0600Z 18.3N 80.7W 85 KTS
36HR VT 08/1800Z 18.5N 83.5W 90 KTS
48HR VT 09/0600Z 18.5N 86.0W 95 KTS
72HR VT 10/0600Z 18.5N 90.0W 45 KTS...INLAND
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