655 
 WTNT42 KNHC 091436
 TCDAT2
  
 HURRICANE KATIA DISCUSSION NUMBER  46
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
 1100 AM AST FRI SEP 09 2011
  
 KATIA HAS MAINTAINED A RAGGED EYE FEATURE IN BOTH CONVENTIONAL AND
 MICROWAVE SATELLITE IMAGERY DURING THE PAST 6 HOURS...SO THE
 INTENSITY WILL REMAIN AT 75 KT...WHICH IS CONSISTENT WITH NHC AODT
 AND SAB INTENSITY ESTIMATES. DESPITE THE HIGH LATITUDE OF THE
 CYCLONE...KATIA CONTINUES TO HAVE A WELL-DEFINED UPPER-LEVEL
 OUTFLOW PATTERN.
 
 THE INITIAL MOTION ESTIMATE IS 050/25 KT. KATIA IS WELL NORTH OF THE
 SUBTROPICAL RIDGE AXIS ORIENTED ALONG 33N LATITUDE...AND WATER
 VAPOR IMAGERY INDICATES THAT THE CYCLONE IS NOW ENTERING THE FAST
 WESTERLY FLOW REGIME THAT LIES NORTH OF 40N LATITUDE. AS A
 RESULT...KATIA IS EXPECTED TO ACCELERATE NORTHEASTWARD THROUGH THE
 REMAINDER OF THE FORECAST PERIOD. THE HURRICANE SHOULD PASS OVER
 MUCH COLDER WATER BY 24 HOURS AND BECOME A POWERFUL EXTRATROPICAL
 CYCLONE. THE FORECAST TRACK IS DOWN THE MIDDLE OF THE TIGHTLY
 PACKED MODEL GUIDANCE...AND LIES CLOSE TO THE NHC CONSENSUS MODEL
 TVCN.
 
 KATIA WILL BE MOVING OVER WATER TEMPERATURES LESS THAN 26C BY 12
 HOURS...AND OVER SSTS LESS THAN 20C BY 24 HOURS. THEREFORE...A
 FAIRLY QUICK TRANSITION TO AN EXTRATROPICAL CYCLONE IS EXPECTED BY
 24 HOURS WHEN THE SYSTEM WILL ALSO BE MERGING WITH AN APPROACHING
 FRONTAL ZONE. ALTHOUGH KATIA IS FORECAST TO WEAKEN BELOW HURRICANE
 FORCE BY 36 HOURS...THE LARGE EXTRATROPICAL LOW PRESSURE SYSTEM IS
 EXPECTED TO CONTAIN STORM-FORCE WINDS WHEN IT APPROACHES THE
 BRITISH ISLES IN 3 DAYS.
 
 NO 96-HOUR FORECAST POINT HAS BEEN PROVIDED DUE TO COMPUTATIONAL
 ISSUES WHEN SYSTEMS MOVE EAST OF ZERO DEGREES LONGITUDE. 
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  09/1500Z 39.3N  65.8W   75 KT  85 MPH
  12H  10/0000Z 41.1N  60.4W   70 KT  80 MPH
  24H  10/1200Z 44.1N  49.9W   65 KT  75 MPH...POST-TROP/EXTRATROP
  36H  11/0000Z 47.8N  37.8W   60 KT  70 MPH...POST-TROP/EXTRATROP
  48H  11/1200Z 51.5N  26.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
  72H  12/1200Z 58.5N   7.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
  96H  13/1200Z...EAST OF ZERO DEGREES LONGITUDE
  
 $$
 FORECASTER STEWART