000
WTNT42 KNHC 070237
TCDAT2
 
HURRICANE KATIA DISCUSSION NUMBER  36
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 PM AST TUE SEP 06 2011
 
SINCE THE AIRCRAFT DEPARTED KATIA THIS AFTERNOON THE SATELLITE
PRESENTATION HAS IMPROVED SLIGHTLY. ALTHOUGH THE CONVECTIVE PATTERN
HAS GAINED CURVATURE...THUNDERSTORM ACTIVITY IS QUITE THIN OVER THE
WESTERN SEMICIRCLE...AS SEEN IN THE LAST FEW MICROWAVE OVERPASSES.
THIS ASYMMETRIC PATTERN IS LIKELY DUE TO SOME WESTERLY SHEAR AND
DRY AIR ENTRAINMENT. THE INITIAL WIND SPEED IS HELD AT 90 KT FOR
THIS ADVISORY...WHICH IS IN AGREEMENT WITH AN AVERAGE OF THE DVORAK
T AND CI NUMBERS.

KATIA IS STILL MOVING NORTHWESTWARD AT ABOUT 8 KT...BUT IS EXPECTED
TO TURN TOWARD THE NORTH WITH AN INCREASE IN FORWARD SPEED DURING
THE NEXT 24 TO 36 HOURS AS THE HURRICANE BECOMES EMBEDDED IN THE
FLOW BETWEEN THE SUBTROPICAL RIDGE AND A LARGE UPPER-LEVEL CUTOFF
LOW OVER THE OHIO VALLEY OF THE UNITED STATES. KATIA IS EXPECTED TO
ACCELERATE TO THE NORTHEAST AND EAST-NORTHEAST IN TWO TO THREE DAYS
AS THE CYCLONE GETS SWEPT UP IN THE STRONG MID-LATITUDE FLOW. THE
MODELS REMAIN IN GOOD AGREEMENT ON THE FUTURE TRACK OF KATIA...AND
THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ONE. THE 96- AND
120-HOUR FORECAST POINTS ARE LARGELY BASED ON GUIDANCE FROM THE
OCEAN PREDICTION CENTER.

LITTLE CHANGE IN STRENGTH OR GRADUAL WEAKENING IS LIKELY DURING THE
NEXT 24 TO 48 HOURS. BEYOND THAT TIME...KATIA WILL BE MOVING OVER
COOLER WATERS AND IS EXPECTED TO ENCOUNTER STRONGER SOUTHWESTERLY
SHEAR. THESE FACTORS SHOULD LEAD TO EXTRATROPICAL TRANSITION...
WHICH IS LIKELY TO OCCUR IN THREE TO FOUR DAYS. ALL OF THE GLOBAL
MODELS SHOW KATIA BECOMING A LARGE AND POWERFUL POST-TROPICAL
CYCLONE OVER THE NORTH ATLANTIC.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/0300Z 28.1N  67.2W   90 KT 105 MPH
 12H  07/1200Z 29.0N  68.3W   85 KT 100 MPH
 24H  08/0000Z 30.6N  69.5W   85 KT 100 MPH
 36H  08/1200Z 32.7N  69.9W   80 KT  90 MPH
 48H  09/0000Z 35.2N  69.2W   80 KT  90 MPH
 72H  10/0000Z 40.0N  62.5W   75 KT  85 MPH
 96H  11/0000Z 45.0N  44.0W   70 KT  80 MPH...POST-TROP/EXTRATROP
120H  12/0000Z 55.0N  25.0W   70 KT  80 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER CANGIALOSI/BRENNAN