487 
 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