Tropical Storm KAREN

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TROPICAL STORM KAREN DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
500 PM EDT WED SEP 26 2007
 
KAREN'S INTENSIFICATION...AT LEAST FOR THE TIME BEING...HAS
HALTED.  THE INTERMITTENT EYE IS NO LONGER PRESENT AND DEEP
CONVECTION IS MAINLY OCCURRING IN THE NORTHEASTERN SEMICIRCLE. 
SUBJECTIVE DVORAK ESTIMATES REMAIN AT 4.0 AND 3.5 FROM TAFB AND
SAB...THOUGH THE ADVANCED DVORAK TECHNIQUE CONTINUES TO SUGGEST AN
INTENSITY A BIT LOWER AT 50-55 KT.  AN 1835Z AMSU CIMSS ESTIMATE
ALSO GIVES A WIND OF 57 KT FOR KAREN. INITIAL INTENSITY IS KEPT AT
60 KT... THOUGH THIS MAY BE SOMEWHAT GENEROUS.

KAREN IS MOVING AT 295/10 UNDER THE INFLUENCE OF A LOW- TO MID-LEVEL
RIDGE TO ITS NORTH.  A TROUGH IN THE UPPER TROPOSPHERE LOCATED WEST
OF KAREN IS PREDICTED TO RETROGRADE WESTWARD AND INDUCE ENOUGH OF A
WEAKNESS IN THE RIDGE TO TURN KAREN TOWARD THE NORTHWEST BETWEEN
DAYS 3 AND 5.  THE MODEL CONSENSUS HAS SHIFTED SLIGHTLY TO THE WEST
IN THE 12Z RUNS.  THE TRACK FORECAST IS CONSISTENT WITH THAT
GUIDANCE EXCEPT TO PUT LESS WEIGHT ON THE GFS EARLY ON...DUE TO ITS
TOO RAPID INITIAL MOTION...AND THE NOGAPS AT DAYS 4 AND 5...DUE TO
ITS UNREALISTICALLY LARGE VORTEX AND NORTHWARD MOTION.

AS IN MANY CASES...THE INTENSITY FORECAST IS NOT CLEAR CUT.  KAREN
REMAINS OVER WARM 28C WATER AND HAS ABUNDANT MOISTURE NEARBY BUT IS
BEING IMPACTED BY MODERATE 15-20 KT WESTERLY SHEAR.  THE SHEAR
SHOULD CONTINUE AND PERHAPS BE ENHANCED DURING THE NEXT THREE DAYS. 
THE SHIPS AND LGM STATISTICAL GUIDANCE SUGGEST MODEST
INTENSIFICATION DURING THE NEXT DAY...BUT THIS MAY BE OVERLY
INFLUENCED BY THEIR PERSISTENCE PREDICTOR.  THE GFDL AND HWRF
DYNAMICAL GUIDANCE ARE LESS IMPRESSED WITH THE POTENTIAL FOR
INTENSIFICATION.  THE OFFICIAL INTENSITY FORECAST BRINGS KAREN TO A
HURRICANE...BUT JUST BARELY...IN A DAY BEFORE A GRADUAL WEAKENING
THEREAFTER.  HOWEVER...IF THE SHEAR CONTINUES TO ADVERSELY IMPACT
KAREN'S ABILITY TO MAINTAIN SYMMETRIC CONVECTION...THEN THE CYCLONE
MAY BE SIGNIFICANTLY WEAKER THAN PREDICTED HERE.

THE 12 FOOT SEAS RADII WERE ADJUSTED OUTWARD BASED UPON OBSERVATIONS
FROM NOAA BUOY 41041.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 12.4N  43.6W    60 KT
 12HR VT     27/0600Z 13.2N  45.1W    60 KT
 24HR VT     27/1800Z 14.6N  47.2W    65 KT
 36HR VT     28/0600Z 15.9N  48.8W    65 KT
 48HR VT     28/1800Z 17.0N  50.1W    60 KT
 72HR VT     29/1800Z 19.0N  52.5W    55 KT
 96HR VT     30/1800Z 21.0N  55.0W    55 KT
120HR VT     01/1800Z 23.0N  57.0W    55 KT
 
$$
FORECASTER LANDSEA/PASCH
 
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