000
WTNT42 KNHC 060847
TCDAT2
 
HURRICANE KATIA DISCUSSION NUMBER  33
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 AM AST TUE SEP 06 2011
 
THE SATELLITE SIGNATURE OF KATIA HAS DECREASED SLIGHTLY IN
ORGANIZATION DURING THE LAST SEVERAL HOURS...WITH THE CLOUD PATTERN
BECOMING LESS SYMMETRIC AND THE EYE LESS DISTINCT AND COOLER. A
TIMELY AMSU-B IMAGE FROM 0544 UTC INDICATED A DOUBLE EYEWALL
STRUCTURE...SUGGESTING THAT KATIA IS AGAIN IN THE MIDST OF ANOTHER
EYEWALL REPLACEMENT. SUBJECTIVE DVORAK INTENSITY ESTIMATES HAVE
DECREASED SOMEWHAT SINCE 0000 UTC.  A BLEND OF THESE AND THE LATEST
ADT VALUES IS THE BASIS FOR THE CURRENT INTENSITY ESTIMATE OF 110
KT.  DURING THE NEXT DAY OR SO...THE LARGE-SCALE ATMOSPHERIC AND
OCEANIC ENVIRONMENT ARE LIKELY TO REMAIN CONDUCIVE FOR KATIA TO
MAINTAIN MAJOR HURRICANE STATUS. HOWEVER...FLUCTUATIONS IN STRENGTH
DUE TO A DIFFICULT-TO-FORECAST INNER CORE EVOLUTION ARE PROBABLE
DURING THIS TIME.  AFTER 48 HOURS...THE HURRICANE WILL BE
ENCOUNTERING AN ENVIRONMENT OF GRADUALLY INCREASING VERTICAL SHEAR
AND LOWER OCEANIC HEAT CONTENT...AND WEAKENING SHOULD COMMENCE.
LATER IN THE FORECAST PERIOD...KATIA SHOULD MOVING NEARLY PARALLEL
TO A STRONG GRADIENT OF SEA SURFACE TEMPERATURE AND WILL BECOME
EMBEDDED IN AN INCREASINGLY BAROCLINIC ENVIRONMENT AS IT NEARS A
MID-LATITUDE JET...BOTH OF WHICH SHOULD PROMOTE ITS TRANSITION TO
AN EXTRATROPICAL CYCLONE. THE OFFICIAL NHC INTENSITY FORECAST IS
CLOSE TO THE PREVIOUS ONE AND SHOWS KATIA AS STRONG CYCLONE THROUGH
EXTRATROPICAL TRANSITION.
 
KATIA APPEARS TO BE EXHIBITING A TROCHOIDAL MOTION...WITH A
SMOOTHING OF RECENT FIXES YIELDING AN INITIAL MOTION ESTIMATE OF
315/9.  VERY LITTLE CHANGE HAS BEEN MADE TO THE NHC FORECAST TRACK
ON THIS PACKAGE.  GLOBAL MODELS SHOW KATIA BEING STEERED AROUND THE
SOUTHWEST SIDE OF A MID-LEVEL RIDGE EAST OF BERMUDA AND TOWARD A
INTO A WEAKNESS OVER THE WESTERN ATLANTIC DURING THE NEXT COUPLE OF
DAYS.  BY 48 HOURS...KATIA SHOULD TURN NORTHWARD ROUGHLY ALONG 70W
IN BETWEEN A LARGE CUT-OFF LOW OVER THE EASTERN UNITED STATES AND
THE RIDGE TO THE EAST.  THE HURRICANE SHOULD THEN ACCELERATE
NORTHEASTWARD AND THEN EAST-NORTHEASTWARD AS IT BECOMES EMBEDDED IN
A FAST AND NEARLY ZONAL FLOW ON THE SOUTH SIDE OF A BROAD TROUGH
COVERING THE FAR NORTH ATLANTIC. THE NEW NHC TRACK FORECAST IS DOWN
THE CENTER OF THE GUIDANCE ENVELOPE THROUGH 72 HOURS AND A BIT TO
THE EAST OF THE MULTI-MODEL CONSENSUS AT LATER TIMES.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  06/0900Z 26.5N  65.1W  110 KT 125 MPH
 12H  06/1800Z 27.4N  66.2W  115 KT 135 MPH
 24H  07/0600Z 28.6N  67.6W  110 KT 125 MPH
 36H  07/1800Z 30.2N  69.0W  105 KT 120 MPH
 48H  08/0600Z 32.0N  69.8W   90 KT 105 MPH
 72H  09/0600Z 36.2N  68.5W   80 KT  90 MPH
 96H  10/0600Z 40.0N  60.0W   75 KT  85 MPH
120H  11/0600Z 44.0N  41.5W   65 KT  75 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER KIMBERLAIN