Tropical Storm KAREN

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TROPICAL STORM KAREN DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
1100 AM EDT WED SEP 26 2007
 
KAREN CONTINUES TO SPIN UP AS A RAGGED EYE HAS BEEN SEEN
INTERMEDITENTLY THIS MORNING IN VISIBLE AND INFRARED IMAGERY. 
SUBJECTIVE DVORAK CLASSIFICATIONS AT 12Z ARE AT 4.0 AND 3.5 FROM
TAFB AND SAB...RESPECTIVELY.  AN AMSU PASS AT 08Z SUGGESTED AROUND
60 KT FROM THE CIMSS TECHNIQUE.  THE ADT...HOWEVER...ANALYSES KAREN
A BIT WEAKER AT ABOUT 50 KT.  GIVEN THE IMPROVED PRESENTATION SINCE
SYNOPTIC TIME...THE INITIAL INTENSITY OF KAREN IS SET AT 60 KT.

THE TROPICAL STORM IS MOVING AT 285/11 SOUTH OF A WEAK DEEP LEVEL
RIDGE.  AN UPPER TROUGH NORTHWEST OF KAREN IS FORECAST BY ALL
MODELS TO SLOWLY RETROGRADE AND PRODUCE ENOUGH OF A WEAKNESS IN THE
RIDGE TO ALLOW THE CYCLONE TO TURN TO THE NORTHWEST.  THE MODEL
GUIDANCE IS TIGHTLY CLUSTERED FOR THE FIRST 48 HOURS.  AT DAYS 3 TO
5...MOST MODELS SLOW KAREN'S PROGRESSION AS THE STEERING FLOW
SLACKENS.  THE MODELS DIFFER AT THE LONG RANGE ON BOTH THE STRENGTH
OF THE CYCLONE'S VORTEX AS WELL AS THE AMPLITUDE OF A SHORTWAVE
TROUGH NEAR BERMUDA.  THE TRACK FORECAST IS CLOSE TO THE CONSENSUS
OF DYNAMICAL MODELS WITH LESS WEIGHT BEING PLACED ON THE NORTHERN
OUTLYING NOGAPS MODEL.

GIVEN THAT THE CYCLONE IS INTENSIFYING...IT APPEARS THAT IT MAY
REACH HURRICANE INTENSITY SOON.  ENVIRONMENTAL CONDITIONS ARE
MIXED.  SSTS ARE A WARM 28C THOUGH THE SHEAR IS ANALYZED TO BE
ABOUT 15 KT OUT OF THE WEST.  THIS SHEAR DOES APPEAR TO BE
RESTRICTING THE WESTERN OUTFLOW OF KAREN.  THE SHEAR IS PREDICTED
BY ALL MODELS TO BE MAINTAINED OR EVEN GET STRONGER AT DAYS 3 TO 5
DUE TO THE INFLUENCE OF THE EARLIER MENTIONED UPPER LEVEL TROUGH. 
THE INTENSITY FORECAST BRINGS KAREN TO A HURRICANE SHORTLY...
LEVELING OFF IN A DAY OR TWO...AND THEN WEAKENING AT DAYS 4 AND 5. 
THIS IS IN AGREEMENT WITH SHIPS AND LGEM BUT STRONGER THAN HWRF AND
GFDL WHICH DO NOT BRING KAREN TO HURRICANE INTENSITY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/1500Z 11.9N  42.9W    60 KT
 12HR VT     27/0000Z 12.6N  44.5W    65 KT
 24HR VT     27/1200Z 14.0N  46.8W    75 KT
 36HR VT     28/0000Z 15.5N  48.5W    75 KT
 48HR VT     28/1200Z 16.8N  50.0W    70 KT
 72HR VT     29/1200Z 19.0N  52.0W    65 KT
 96HR VT     30/1200Z 21.0N  54.0W    60 KT
120HR VT     01/1200Z 23.0N  55.5W    55 KT
 
$$
FORECASTER LANDSEA/PASCH
 
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