[Tropical] Tropical Cyclone Discussion

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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


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