000
WTNT42 KNHC 270841
TCDAT2
TROPICAL STORM KAREN DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
500 AM EDT THU SEP 27 2007
 
THE STRONG SOUTHWESTERLY SHEAR HAS TAKEN A TOLL ON KAREN THIS
MORNING.  RECENT TRMM AND AMSU-B MICROWAVE PASSES SUGGEST THAT THE
LOW-LEVEL CIRCULATION CENTER HAS CONTINUED TO BECOME DECOUPLED FROM
THE MID- AND UPPER-LEVELS.  CONVENTIONAL SATELLITE IMAGERY INDICATE
AN ELONGATED AREA OF DEEP CONVECTION ABOUT 60 N MI NORTHEAST OF THE
CENTER...EXTENDING NORTHEASTWARD FOR A COUPLE OF HUNDRED MILES. 
DVORAK SATELLITE INTENSITY CLASSIFICATIONS ARE 3.0/4.0 FROM TAFB AND
3.0/3.5 FROM SAB.  TAKING A BLEND OF THE INTENSITY ESTIMATES ALONG
WITH THE CURRENT SATELLITE APPEARANCE...THE INITIAL INTENSITY HAS
BEEN LOWERED TO 55 KT.  

THE INITIAL MOTION IS SLIGHTLY FASTER...ABOUT 300/13.  A WEAK RIDGE
NORTH OF THE CYCLONE IS EXPECTED TO PERSIST FOR THE NEXT DAY OR SO
WHICH SHOULD RESULT IN A GENERAL WEST-NORTHWESTWARD MOTION.  AFTER
24- TO 36-HOURS...LARGE DIVERGENCE IN MODEL GUIDANCE EXISTS WHEN A
DEEP MID- TO UPPER-LEVEL TROUGH APPROACHES FROM THE WEST.  ONE
GROUP OF MODELS MAINTAINS KAREN AS A STRONGER CYCLONE AND TAKES THE
SYSTEM TOWARD THE NORTHWEST IN RESPONSE TO THE TROUGH.  THE SECOND
GROUP FORECAST KAREN AS A MUCH WEAKER SYSTEM AND STEER IT WITH THE
LOW-LEVEL FLOW.  THE OFFICIAL TRACK FORECAST FOLLOWS THE LATTER
SOLUTION...WHICH IS CLOSE WITH THE GFS AS WELL AS THE PREVIOUS
ADVISORY PACKAGE. 

THE SHEAR IS EXPECTED TO REMAIN STRONG FOR THE NEXT 72 HOURS OR
SO...WHICH WOULD LEAD TO A CONTINUED WEAKENING TREND OF THE
CYCLONE.  BY DAYS 4 AND 5...MOST OF THE MODEL GUIDANCE FORECASTS
THE SHEAR TO DECREASE.  HOWEVER...THE DECREASED SHEAR APPEARS TO BE
RESULTANT OF KAREN APPROACHING THE AXIS OF THE AFOREMENTIONED
TROUGH...WHICH WOULD NOT BE CONDUCIVE FOR MUCH STRENGTHENING
EITHER.  SIMILAR TO THE PREVIOUS FORECAST...THE OFFICIAL INTENSITY
FORECAST CALLS FOR GRADUAL WEAKENING THROUGH FIVE DAYS.  BUT...IF
THE LOW-LEVEL CIRCULATION CENTER BECOMES FURTHER SEPARATED FROM THE
DEEP CONVECTION...THE CYCLONE COULD WEAKER FASTER THAN INDICATED. 

NOAA BUOY 41041 REPORTED A MAXIMUM 1-MINUTE WIND OF 43 KT AROUND
0700 UTC...ABOUT 75 N MI NORTH OF THE ESTIMATED CENTER LOCATION.  

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 13.6N  46.6W    55 KT
 12HR VT     27/1800Z 14.6N  48.3W    50 KT
 24HR VT     28/0600Z 15.8N  50.2W    50 KT
 36HR VT     28/1800Z 16.9N  51.9W    45 KT
 48HR VT     29/0600Z 18.1N  53.7W    45 KT
 72HR VT     30/0600Z 20.0N  56.0W    40 KT
 96HR VT     01/0600Z 21.5N  57.5W    40 KT
120HR VT     02/0600Z 23.0N  59.0W    40 KT
 
$$
FORECASTER MAINELLI