185 
 WTNT42 KNHC 050853
 TCDAT2
  
 HURRICANE KATIA DISCUSSION NUMBER  29
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
 500 AM AST MON SEP 05 2011
  
 THE INNER CORE CONVECTIVE STRUCTURE OF KATIA APPEARS TO HAVE GONE
 THROUGH ANOTHER ROUND OF CHANGES...WITH A NET DECREASE IN
 ORGANIZATION NOTED DURING THE PAST SEVERAL HOURS.  AN EYE THAT WAS
 EVIDENT EARLIER IS NO LONGER APPARENT...AND THERE ARE SIGNS THAT
 DRY AIR HAS BEEN ROTATING AROUND THE CIRCULATION. UPPER-LEVEL
 OUTFLOW IS GOOD TO EXCELLENT...WITH A FAVORABLE OUTFLOW SINK TO THE
 NORTHEAST.  A BLEND OF DVORAK T AND CI NUMBERS FROM TAFB AND SAB IS
 LOWER THAN 6 HOURS AGO...SO THE CURRENT INTENSITY ESTIMATE IS
 LOWERED TO 85 KT.
  
 THE CENTER OF KATIA HAS BEEN WOBBLING. SMOOTHING OF RECENT FIXES
 YIELDS AN INITIAL MOTION ESTIMATE OF 305/10. LARGE-SCALE MODELS
 SHOW KATIA ROUNDING THE SOUTHWEST PERIPHERY OF A MID-LEVEL RIDGE
 EAST OF BERMUDA...HEADING TOWARD A WEAKNESS OVER THE WESTERN
 ATLANTIC. THIS SYNOPTIC PATTERN SHOULD STEER THE HURRICANE ON A
 GENERAL NORTHWESTWARD COURSE WITH SOME DECELERATION OVER THE NEXT
 FEW DAYS. LATER IN THE FORECAST PERIOD...FURTHER WESTWARD PROGRESS
 IS LIKELY TO BE BLOCKED AS KATIA IS CAUGHT UP IN DEEP-LAYER
 SOUTHERLY FLOW IN BETWEEN A LARGE CUT-OFF LOW OVER THE EASTERN
 UNITED STATES AND THE RIDGE TO THE EAST. ONCE KATIA GAINS ENOUGH
 LATITUDE...GLOBAL MODELS SHOW THE HURRICANE BECOMING EMBEDDED IN 
 STRONG MID-LATITUDE WESTERLY FLOW AND ACCELERATING NORTHEASTWARD.
 THE SPREAD IN THE TRACK GUIDANCE HAS DECREASED SUBSTANTIALLY SINCE
 YESTERDAY AND NOW FAVORS A RECURVATURE SCENARIO ROUGHLY ALONG
 70W...WITH EVEN THE LEFT-LEANING UKMET/ECMWF MODELS NOW SHIFTING
 SIGNIFICANTLY TO THE EAST. THE MAIN FORECAST CHALLENGE IS HOW
 QUICKLY KATIA WILL TURN NORTHWARD AND THEN NORTHEASTWARD...WITH
 MAJOR TIMING DIFFERENCES NOTED AMONGST THE VARIOUS MODELS. THE
 OFFICIAL TRACK IS NEARLY IDENTICAL TO THE PREVIOUS ONE THROUGH 72
 HOURS BUT IS ADJUSTED TO THE RIGHT AND IS MUCH FASTER TOWARD THE
 END OF THE PERIOD BUT NOT AS FAST AS THE MULTI-MODEL CONSENSUS.
  
 ACCORDING TO THE GLOBAL MODELS...KATIA WILL BE MOVING THROUGH AN
 ENVIRONMENT CHARACTERIZED BY ANTICYCLONIC UPPER-LEVEL FLOW AND WEAK
 VERTICAL SHEAR THROUGH AT LEAST 72 HOURS. THE PRIMARY NEGATIVE
 FACTORS THAT COULD INHIBIT THE INTENSIFICATION PROCESS DURING THIS
 TIME ARE LOW MID-LEVEL RELATIVE HUMIDITY VALUES...A LOWERING OF THE
 OCEANIC HEAT CONTENT ALONG THE FORECAST TRACK...AND THE POSSIBILITY
 OF A MORE STABLE ENVIRONMENT DUE TO WARMING ALOFT.  AFTER 96
 HOURS...INCREASING SHEAR AND THE PROXIMITY OF KATIA TO A STRONG
 GRADIENT OF SEA SURFACE TEMPERATURES WILL LIKELY CONTRIBUTE TO
 WEAKENING. THE OFFICIAL INTENSITY FORECAST HAS BEEN LOWERED EARLY
 IN THE FORECAST PERIOD BASED ON CURRENT TRENDS AND ALSO AT THE END
 OF THE PERIOD AS A RESULT OF ADJUSTMENTS TO THE TRACK FORECAST. 
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  05/0900Z 23.9N  62.0W   85 KT 100 MPH
  12H  05/1800Z 25.0N  63.2W   90 KT 105 MPH
  24H  06/0600Z 26.3N  64.8W   95 KT 110 MPH
  36H  06/1800Z 27.5N  66.2W  100 KT 115 MPH
  48H  07/0600Z 28.6N  67.6W  105 KT 120 MPH
  72H  08/0600Z 31.4N  70.1W  100 KT 115 MPH
  96H  09/0600Z 35.5N  69.5W   90 KT 105 MPH
 120H  10/0600Z 38.5N  64.0W   75 KT  85 MPH
  
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 FORECASTER KIMBERLAIN