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Tropical Storm KAREN


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TROPICAL STORM KAREN DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
1100 AM EDT FRI SEP 28 2007
 
VISIBLE IMAGERY SUGGESTS THAT THE WEAKENING CIRCULATION OF KAREN HAS
MOVED ERRATICALLY THIS MORNING...BUT NOW APPEARS TO BE RETURNING TO
A PREVIOUS WEST-NORTHWESTWARD MOTION.  AN EARLIER 0910Z QUIKSCAT
OVERPASS INDICATED THAT THERE WAS A SMALL AREA OF BELIEVABLE
FLAGGED 40 KT WINDS IN THE NORTHEAST QUADRANT.  BUT SINCE
THEN...THAT CONVECTIVE AREA CONTAINING THE COLDEST TOPS HAS
DIMINISHED CONSIDERABLY.  BASED ON THE QUIKSCAT INTERPRETATION AND
CURRENT SATELLITE INTENSITY ESTIMATES OF 35 KT...THE INITIAL
INTENSITY IS LOWERED TO 35 KT...AND THIS COULD BE GENEROUS.
 
PERSISTENTLY STRONG SOUTHWESTERLY SHEAR IS EXPECTED TO AFFECT KAREN
DURING THE NEXT 72 HOURS OR SO.  THEREAFTER...THE INTENSITY GUIDANCE
AGREES IN BRINGING UNFAVORABLE UPPER-LEVEL NORTHWESTERLY WINDS OVER
THE SYSTEM.  THE OFFICIAL FORECAST INDICATES WEAKENING TO A
DEPRESSION IN 12 HOURS...FOLLOWING THE SHIPS AND LGEM.
AFTERWARD...BECAUSE OF THE POTENTIAL OF INTERMITTENT BURSTS OF DEEP
CONVECTION NEAR THE CENTER...THE FORECAST SHOWS LITTLE CHANGE IN
STRENGTH.  HOWEVER...KAREN COULD BECOME A REMNANT LOW IN 36
HOURS...AS INDICATED BY BOTH AFOREMENTIONED INTENSITY MODELS.  IN
PREVIOUS RUNS...DESPITE THE OBVIOUS UNFAVORABLE UPPER LEVEL
WIND ENVIRONMENT...SOME DYNAMICAL MODELS SUGGESTED SIGNIFICANT
STRENGTHENING.  HOWEVER...IN THE LATEST RUNS...THE GFS WEAKENS KAREN
AND THIS IS A MORE REALISTIC SCENARIO.  ECMWF AND GFDL INSIST ON
STRENGTHENING.  WE SHALL SEE IN THE NEXT RUN IF THESE MODELS COME TO
AN AGREEMENT WITH THE GFS.
 
INITIAL MOTION IS ESTIMATED AT 295/8.  A LOW- TO MID LEVEL
TROPOSPHERIC SUBTROPICAL RIDGE TO THE NORTH OF KAREN SHOULD
MAINTAIN A WEST-NORTHWESTWARD MOTION DURING THE NEXT 2 DAYS. 
AFTERWARD...A DEVELOPING WEAKNESS IN THE RIDGE NORTHWEST OF THE
CYCLONE SHOULD TEMPORARILY INDUCE A MORE NORTHWESTWARD MOTION.
AROUND THE 96 HOUR PERIOD...ALL OF THE DYNAMICAL MODELS ARE
INDICATING THAT THE TROUGH WILL FILL AND MOVE NORTHEAST ALLOWING A
MID- LEVEL HIGH TO BUILD SOUTHEAST OF BERMUDA.  THIS CHANGE IN THE
STEERING PATTERN SHOULD CAUSE KAREN TO TURN MORE TO THE WEST...IF
THE CYCLONE SURVIVES FOR THAT LONG OF A PERIOD.  THE OFFICIAL TRACK
FORECAST IS CLOSE TO THE PREVIOUS PACKAGE AND IS BASED ON A BLEND OF
THE MODEL CONSENSUS...AND HEDGES TOWARD THE SHALLOW MEAN LAYER
BAM....SINCE THE KAREN IS FORECAST TO WEAKEN.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/1500Z 15.1N  49.2W    35 KT
 12HR VT     29/0000Z 15.5N  50.5W    30 KT
 24HR VT     29/1200Z 16.6N  52.0W    30 KT
 36HR VT     30/0000Z 17.6N  53.3W    30 KT
 48HR VT     30/1200Z 18.5N  54.6W    30 KT
 72HR VT     01/1200Z 20.0N  56.5W    30 KT
 96HR VT     02/1200Z 21.5N  58.0W    30 KT
120HR VT     03/1200Z 22.0N  60.0W    30 KT
 
$$
FORECASTER ROBERTS
 
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