[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 130901
TCDAT4
TROPICAL STORM IRENE DISCUSSION NUMBER  35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SAT AUG 13 2005

A DEEP BURST OF CONVECTION BEGAN AT ABOUT 04Z... AND THE COLDEST
CONVECTIVE TOPS REMAIN LESS THAN -70 DEGREES CELSIUS.  AN AIR FORCE
RECONNAISSANCE AIRCRAFT LOCATED THE CIRCULATION CENTER JUST NORTH
OF THIS DEEP CONVECTION... AND MAXIMUM 850 MB FLIGHT LEVEL WINDS OF
69 KT WITHIN IT... WHICH CORRESPONDS TO SURFACE WINDS OF 55 KT.
THE AIRCRAFT ALSO MEASURED A MINIMUM CENTRAL PRESSURE A BIT HIGHER
THAN PREVIOUSLY THOUGHT... 997 MB.  DVORAK DATA T NUMBERS ARE
UNANIMOUSLY 3.5/55 KT.  WHILE THERE ARE NO HARD NUMBERS TO SUPPORT
MAINTAINING THE INTENSITY AT 60 KT... I WILL DO SO BASED ON THE
CONVECTIVE ORGANIZATION NEAR THE CIRCULATION CENTER.

AIRCRAFT FIXES DURING THE PAST FEW HOURS INDICATE THAT IRENE IS
STILL MOVING NORTHWESTWARD... BUT A LITTLE FARTHER EAST THAN THE
PREVIOUS FORECAST TRACK... WITH INITIAL MOTION NOW ESTIMATED AT
320/9.  IRENE IS BEING STEERED AROUND A NEARBY DEEP LAYER RIDGE
CENTERED OVER BERMUDA.  DATA FROM LAST NIGHT'S SYNOPTIC
SURVEILLANCE MISSION DOES NOT SEEM TO HAVE LED TO ANY SIGNIFICANT
CHANGES TO EITHER THE INITIAL CONDITIONS OR THE FORECASTS FROM THE
VARIOUS DYNAMICAL MODELS.  THE MODELS REMAIN IN GENERAL AGREEMENT
THAT IRENE WILL ROUND THE RIDGE AND TURN TOWARD THE NORTH DURING
THE NEXT 36 HOURS AND NORTHEASTWARD BEYOND 72 HOURS.  NONE OF THE
MODELS INDICATE LANDFALL ON THE EAST COAST OF THE UNITED STATES.
DUE TO THE INITIAL MOTION ADJUSTMENT AND TO A SLIGHT EASTWARD TREND
IN THE MODEL TRACKS... THE OFFICIAL FORECAST IS ADJUSTED TO THE
RIGHT OR EAST OF THE PREVIOUS ADVISORY DURING THE FIRST THREE DAYS.
IT IS ALSO FASTER SINCE IRENE IS GAINING LATITUDE MORE QUICKLY NOW
AND WILL BECOME EMBEDDED IN THE WESTERLIES TO THE NORTH OF THE
RIDGE AND BEGIN ACCELERATING ON DAY 4... AS SHOWN BY ALL OF THE
MODELS EXCEPT THE LEFT-OUTLYING GFDN.

SINCE IRENE IS STILL ON THE CUSP OF BECOMING A HURRICANE... IT COULD
DO SO AT ANY TIME.  THE SHIPS PEAKS AT 63 KT IN 72 HOURS... WHILE
THE GFDL PEAKS NEAR 80 KT AROUND THAT SAME TIME.  THE OFFICIAL
INTENSITY FORECAST IS ADJUSTED ONLY SLIGHTLY DOWNWARD COMPARED TO
THE PREVIOUS ADVISORY... TO COME MORE IN LINE WITH SHIPS.  SINCE
THE NEW OFFICIAL FORECAST IS FASTER... IRENE IS EXPECTED TO REACH
COOLER WATERS SOONER... SO A WEAKENING TREND IS INTRODUCED AT THE
END OF THE FORECAST... IN ACCORDANCE WITH BOTH GFDL AND SHIPS.

FORECASTER KNABB


FORECAST POSITIONS AND MAX WINDS

INITIAL      13/0900Z 30.1N  68.6W    60 KT
 12HR VT     13/1800Z 31.0N  69.3W    65 KT
 24HR VT     14/0600Z 32.6N  69.8W    65 KT
 36HR VT     14/1800Z 34.2N  69.8W    70 KT
 48HR VT     15/0600Z 36.0N  69.2W    70 KT
 72HR VT     16/0600Z 38.0N  66.5W    75 KT
 96HR VT     17/0600Z 39.5N  62.0W    70 KT
120HR VT     18/0600Z 41.5N  54.0W    60 KT


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