598 
 WTNT42 KNHC 070849
 TCDAT2
  
 HURRICANE KATIA DISCUSSION NUMBER  37
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
 500 AM AST WED SEP 07 2011
  
 THE CLOUD PATTERN OF KATIA HAS BECOME A LITTLE LESS ORGANIZED
 OVERNIGHT. CLOUD TOP TEMPERATURES HAVE GENERALLY BEEN WARMING AND
 DRY AIR APPEARS TO WRAPPING AROUND THE WESTERN SEMICIRCLE OF THE
 CIRCULATION...THE LATTER GIVING THE CYCLONE A SOMEWHAT HOLLOW
 APPEARANCE. IN ADDITION...THERE APPEARS TO BE NORTHWESTERLY SHEAR
 OVER THE HURRICANE...AS EVIDENCED BY CIRRUS CLOUD MOTIONS AND
 CONFIRMED BY UW-CIMSS ANALYSES. DVORAK T- AND CI-NUMBERS FROM TAFB
 AND SAB ARE LOWER...AND A REASONABLE BLEND OF THESE DATA GIVES AN
 INTENSITY ESTIMATE OF 80 KT. AN EYEWALL REPLACEMENT CYCLE THAT
 BEGAN 24-36 HOURS APPEARS TO HAVE BEEN INTERRUPTED...WITH EARLIER
 MICROWAVE IMAGERY SHOWING AN OUTER EYEWALL AT LARGE RADIUS THAT WAS
 NOT CONTRACTING MUCH. THIS STRUCTURE...ALONG WITH THE MODERATE
 SHEAR...SUGGESTS NOT MUCH CHANGE IN STRENGTH...FOLLOWED BY ONLY A
 SLOW WEAKENING DURING THE NEXT FEW DAYS AS KATIA REMAINS OVER
 RELATIVELY WARM WATERS. AFTER 72 HOURS...KATIA WILL QUICKLY MOVE
 ALONG A STRONG GRADIENT OF SSTS AND ENCOUNTER AN INCREASINGLY
 BAROCLINIC ENVIRONMENT...BOTH OF WHICH SHOULD RESULT IN A RAPID
 TRANSITION TO AN INTENSE EXTRATROPICAL CYCLONE. POST-TROPICAL
 CYCLONE KATIA IS EXPECTED TO BE A SIGNIFICANT WEATHER SYSTEM OVER
 THE FAR NORTH ATLANTIC FOR AT LEAST A COUPLE OF DAYS. THE OFFICIAL
 NHC WIND SPEED FORECAST IS LOWERED IN ACCORDANCE WITH THE LATEST
 INTENSITY GUIDANCE AND IS IN BEST AGREEMENT WITH THE MODEL
 CONSENSUS.
  
 THE INITIAL MOTION IS A FAIRLY SLOW 315/08. GLOBAL MODELS SHOW KATIA
 GRADUALLY TURNING FROM NORTHWESTWARD TO NORTHWARD INTO A WEAKNESS
 IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC DURING THE NEXT
 24-36 HOURS. AFTER THAT...THE HURRICANE IS EXPECTED TO GRADUALLY
 RECURVE INTO THE WESTERLIES AND ACCELERATE NORTHEASTWARD ON THE
 SOUTH SIDE OF A BROAD TROUGH COVERING THE FAR NORTH ATLANTIC. THE
 TRACK GUIDANCE HAS CONSISTENTLY BEEN HANDLING THE STEERING FLOW
 AROUND THE STORM WELL FOR SEVERAL FORECAST CYCLES AND IS TIGHTLY
 CLUSTERED...GIVING HIGH CONFIDENCE TO THE FORECAST. ONLY MINOR
 CHANGES WERE MADE TO THE PREVIOUS FORECAST TRACK...WITH THE CURRENT
 NHC TRACK AGAIN CLOSE TO THE MULTI-MODEL CONSENSUS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  07/0900Z 28.7N  67.9W   80 KT  90 MPH
  12H  07/1800Z 29.8N  69.0W   80 KT  90 MPH
  24H  08/0600Z 31.7N  69.6W   75 KT  85 MPH
  36H  08/1800Z 34.0N  69.5W   75 KT  85 MPH
  48H  09/0600Z 36.4N  67.9W   70 KT  80 MPH
  72H  10/0600Z 40.9N  58.2W   65 KT  75 MPH
  96H  11/0600Z 47.0N  38.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 120H  12/0600Z 59.0N  17.5W   65 KT  75 MPH...POST-TROP/EXTRATROP
  
 $$
 FORECASTER KIMBERLAIN/PASCH