[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 012045
TCDAT4
HURRICANE ISAAC DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092006
500 PM EDT SUN OCT 01 2006

ISAAC REMAINS A FAIRLY WELL-DEFINED HURRICANE IN SATELLITE IMAGERY
THIS AFTERNOON.  VISIBLE IMAGERY SHOWS A BANDING TYPE EYE AND A
INFRARED IMAGERY DEPICTS AN IMPRESSIVE CDO FEATURE WITH TOPS AS
COLD AS -70C.  A BLEND OF DVORAK CURRENT INTENSITY AND DATA
T-NUMBERS SUPPORTS AN INITIAL INTENSITY OF 70 KT.  INCREASING SHEAR
AND SIGNIFICANTLY COOLER SSTS ALONG THE FORECAST TRACK OF ISAAC ARE
EXPECTED TO GRADUALLY WEAKEN THE TROPICAL CYCLONE DURING THE NEXT
24 HOURS.  THEREAFTER...ISSAC IS FORECAST TO BECOME A STRONG
EXTRATROPICAL CYCLONE AS A BAROCLINIC SYSTEM WILL LIKELY PROVIDE
ADDITIONAL ENERGY AFTER ISAAC LOSES ITS TROPICAL CHARACTERISTICS.
THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY.

ISAAC HAS TURNED NORTHWARD AND IS ACCELERATING.  THE INITIAL MOTION
ESTIMATE IS 005/18 KT.  ISAAC IS EXPECTED TO CONTINUE ACCELERATING
NORTH-NORTHEASTWARD AHEAD OF A LARGE DEEP-LAYER TROUGH THAT IS
EXITING THE EAST COAST OF THE UNITED STATES.  TRACK MODEL GUIDANCE
HAS SHIFTED CONSIDERABLY WESTWARD AND ALL THE MODELS NOW SHOW
LANDFALL IN NEWFOUNDLAND.  THE UKMET AND GFS REMAIN ON THE WEST
SIDE OF THE MODEL GUIDANCE WHILE THE NOGAPS AND GFDL ARE TO THE
EAST...AND FORECAST A TRACK NEAR CAPE RACE NEWFOUNDLAND.  THE
OFFICIAL TRACK WAS ADJUSTED WEST OF THE PREVIOUS ADVISORY AND IS
ALONG THE GUNA MODEL CONSENSUS.  AS WAS THE CASE THIS MORNING...
AFTER THE PASSAGE OVER NEWFOUNDLAND...THE MODELS CONTINUE TO DIVERGE
ON WHICH LOW BECOMES DOMINANT...THE EXTRATROPICAL REMNANT OF ISAAC
OR THE BAROCLINIC LOW DEVELOPING OFF THE NORTHEAST UNITED STATES
COAST.  THIS FORECAST ASSUMES THE SMALLER ISAAC WILL BECOME
ABSORBED BY THE LARGE BAROCLINIC LOW AND THE 72 HOUR FORECAST
CONTINUES TO REFLECT THIS SCENARIO.

REGARDLESS OF WHETHER ISAAC IS A TROPICAL OR EXTRATROPICAL CYCLONE
WHEN PASSING NEAR OR OVER NEWFOUNDLAND...IT WILL LIKELY PRODUCE
SUSTAINED WINDS OF TROPICAL STORM FORCE OVER THAT AREA.

FORECAST POSITIONS AND MAX WINDS

INITIAL      01/2100Z 36.3N  60.0W    70 KT
 12HR VT     02/0600Z 39.7N  59.1W    65 KT
 24HR VT     02/1800Z 45.1N  56.2W    60 KT...EXTRATROPICAL
 36HR VT     03/0600Z 49.5N  52.0W    55 KT...EXTRATROPICAL
 48HR VT     03/1800Z 52.5N  47.0W    50 KT...EXTRATROPICAL
 72HR VT     04/1800Z...ABSORBED

$$
FORECASTER BROWN/FRANKLIN



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