[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 272035
TCDAT2
TROPICAL STORM KAREN DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
500 PM EDT THU SEP 27 2007

PERSISTENTLY STRONG SOUTHWESTERLY SHEAR CONTINUES TO AFFECT THE
TROPICAL CYCLONE...DISPLACING THE DEEP CONVECTION FROM THE
CIRCULATION CENTER.  ALTHOUGH DVORAK SATELLITE INTENSITY ESTIMATES
FROM TAFB AND SAB HAVE DECREASED TO 45 KT...SOME RECENT DEEP
CONVECTIVE BURSTS NEAR THE CENTER SUGGEST A SLIGHTLY HIGHER
INTENSITY.  THEREFORE...THE INITIAL WIND SPEED IS SET TO 50 KT.

THE INTENSITY FORECAST IS RELATIVELY STRAIGHTFORWARD THROUGH DAY
5...INDICATING GRADUAL WEAKENING.  HOWEVER...LARGE-SCALE DYNAMICAL
MODELS...SHIPS...AND THE LGEM ARE NOW SUGGESTING THAT THE SHEAR
WILL BEGIN TO WEAKEN AROUND THE 96 TO 120 HR PERIOD WHEN THE
TROPICAL CYCLONE REACHES THE UPPER TROUGH AXIS.  CONSEQUENTLY...
SLIGHT INTENSIFICATION IN THE LATTER PART OF THE PERIOD IS
POSSIBLE...ALBEIT NOT INDICATED IN THE OFFICIAL FORECAST AT THIS
TIME.

KAREN IS MOVING AT 305/11...WITH THIS GENERAL MOTION CONTINUING
DURING THE NEXT 2 DAYS OR SO AS KAREN PROPAGATES WITHIN THE
DEEP-LAYERED FLOW ASSOCIATED WITH THE SUBTROPICAL RIDGE TO THE
NORTH.  THROUGH THE REMAINING PORTION OF THE FORECAST...THE
DYNAMICAL MODELS ARE AGREEING IN BUILDING THE MID- LEVEL RIDGE MORE
TOWARD THE NORTHWEST OF THE CYCLONE CAUSING KAREN TO TURN MORE
WEST-NORTHWESTWARD.  THE OFFICIAL FORECAST IS CLOSE TO THE PREVIOUS
PACKAGE AND IS BASED ON A CONSENSUS OF THE MODELS.

FORECAST POSITIONS AND MAX WINDS

INITIAL      27/2100Z 14.3N  48.5W    50 KT
 12HR VT     28/0600Z 15.5N  49.8W    45 KT
 24HR VT     28/1800Z 16.8N  51.5W    45 KT
 36HR VT     29/0600Z 17.8N  52.8W    45 KT
 48HR VT     29/1800Z 18.7N  54.0W    45 KT
 72HR VT     30/1800Z 20.5N  55.5W    40 KT
 96HR VT     01/1800Z 22.5N  56.5W    40 KT
120HR VT     02/1800Z 24.0N  58.5W    40 KT

$$
FORECASTER ROBERTS/AVILA



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