000 WTNT42 KNHC 061445 TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 AM AST TUE SEP 06 2011 MICROWAVE IMAGERY FROM OVERNIGHT INDICATES THAT KATIA HAS GONE THROUGH A CLASSIC EYEWALL REPLACEMENT WITH A WIDE RING OF DEEP CONVECTION ENCLOSING A SMALLER AND ERODING INNER EYEWALL. AS WOULD BE EXPECTED IN A CASE LIKE THIS...DVORAK FINAL T-NUMBERS HAVE DECREASED TO BETWEEN 5.0 AND 5.5...AND CI NUMBERS REMAIN AT 6.0. THE INITIAL INTENSITY IS BEING SET AT 105 KT BASED ON A BLEND OF THESE NUMBERS. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS SCHEDULED TO INVESTIGATE KATIA THIS AFTERNOON. ALTHOUGH THE CENTER OF KATIA CONTINUES TO WOBBLE...THE SMOOTHED INITIAL MOTION IS 310/9 KT. THERE HAS BEEN LITTLE CHANGE IN THE TRACK FORECAST OR THE REASONING BEHIND IT. THE HURRICANE IS STILL EXPECTED TO MAKE A TURN TOWARD THE NORTH-NORTHWEST AND NORTH OVER THE NEXT 2 DAYS AS IT IS STEERED BETWEEN THE BERMUDA HIGH AND A CLOSED MID- TO UPPER-LEVEL LOW OVER THE TENNESSEE AND OHIO VALLEYS. THE GUIDANCE HAS SHIFTED SOMEWHAT TO THE NORTHWEST AT 72 HOURS... SUGGESTING THAT THE RE-CURVATURE MAY NOT BE QUITE AS SHARP AS PREVIOUSLY SHOWN. THE OFFICIAL FORECAST HAS BEEN NUDGED IN THAT DIRECTION BUT LIES TO THE SOUTHEAST OF THE TVCA AND EXPERIMENTAL TV15 CONSENSUS MODELS. AFTER 72 HOURS...KATIA IS EXPECTED TO BECOME EMBEDDED IN THE MID-LATITUDE WESTERLIES. THE MODELS ARE STILL SHOWING SOME DIVERGENCE IN SPEED AT 96 AND 120 HOURS...BUT THE SPREAD IS NOT AS LARGE AS IT HAS BEEN IN PREVIOUS DAYS. ONLY A SLIGHT NORTHWARD ADJUSTMENT WAS REQUIRED AT DAY 5. SINCE KATIA IS GOING THROUGH AN EYEWALL REPLACEMENT AND WILL BE LEFT WITH A LARGE RADIUS OF MAXIMUM WINDS...THE MOST LIKELY SCENARIO WOULD BE FOR THE HURRICANE TO CHANGE LITTLE IN STRENGTH IN THE SHORT TERM. GRADUAL WEAKENING SHOULD COMMENCE BY 36 HOURS AS KATIA IS EXPECTED TO BE MOVING OVER WATERS OF LOWER OCEANIC HEAT CONTENT OVER THE WESTERN ATLANTIC...AND POSSIBLY BE AFFECTED BY STRONGER SHEAR. BY DAYS 4 AND 5...BAROCLINIC FORCING SHOULD PREVENT KATIA FROM WEAKENING TOO MUCH...EVEN OVER COLDER WATERS...AND THE CYCLONE IS FORECAST TO BE A POWERFUL EXTRATROPICAL STORM OVER THE NORTH ATLANTIC. THE INTENSITY GUIDANCE IS IN FAIRLY GOOD AGREEMENT...AND THE OFFICIAL FORECAST IS MAINLY JUST AN UPDATE OF THE PREVIOUS FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 27.0N 65.9W 105 KT 120 MPH 12H 07/0000Z 27.9N 67.0W 105 KT 120 MPH 24H 07/1200Z 29.2N 68.5W 105 KT 120 MPH 36H 08/0000Z 30.9N 69.6W 95 KT 110 MPH 48H 08/1200Z 32.9N 70.1W 85 KT 100 MPH 72H 09/1200Z 37.5N 67.5W 75 KT 85 MPH 96H 10/1200Z 41.5N 56.0W 70 KT 80 MPH 120H 11/1200Z 49.0N 35.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ FORECASTER BERG/AVILA