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Hurricane KATIA (Text)

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HURRICANE KATIA DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST MON SEP 05 2011
 
VISIBLE SATELLITE IMAGERY SHOWS THAT KATIA HAS BECOME MORE ORGANIZED
THROUGH THE DAY WITH A WELL-DEFINED EYE AND EXCELLENT UPPER-LEVEL
OUTFLOW...ESPECIALLY OVER THE SOUTHERN SEMICIRCLE.  HOWEVER...THE
INFRARED PRESENTATION IS LAGGING A BIT AND SHOWS A THINNING OF THE
DEEP CONVECTION OVER THE NORTHEASTERN QUADRANT.  DVORAK ESTIMATES
FROM TAFB AND SAB ARE T5.5...AND THE INITIAL INTENSITY IS THEREFORE
RAISED TO 100 KT.  OBJECTIVE DVORAK NUMBERS HAVE BEEN RUNNING
HIGHER...BUT WITH THE CONVECTION LACKING SYMMETRY AND A COOLING EYE
IN THE LAST FEW IMAGES...I WOULD RATHER WAIT TO RAISE THE INTENSITY
ANY HIGHER.
 
THE 12-HOUR SMOOTHED MOTION IS ABOUT 310/10 KT...AND KATIA IS
EXPECTED TO CONTINUE ON ITS NEARLY STRAIGHT TRACK FOR THE NEXT 48
HOURS AS IT MOVES AROUND A CENTRAL ATLANTIC MID-LEVEL ANTICYCLONE. 
FAIRLY SHARP RE-CURVATURE IS SHOWN BY MOST OF THE MODELS AROUND DAY
3...AND THEY ARE TIGHTLY CLUSTERED WITH A TRACK THAT TAKES THE
CENTER ALMOST MIDWAY BETWEEN BERMUDA AND THE U.S. EAST COAST.  AS
WAS THE CASE EARLIER TODAY...THERE IS STILL GREATER-THAN-NORMAL
SPREAD IN THE GUIDANCE AT 96 AND 120 HOURS DUE TO A LACK OF
AGREEMENT ON WHEN KATIA WILL BE SCOOPED UP BY STRONG MID-LATITUDE
WESTERLIES TO THE NORTH.  HOWEVER...THE ECMWF AND UKMET HAVE SPED
UP A BIT AND THE GFS HAS SLOWED DOWN...SO THE UNCERTAINTY HAS
DECREASED SOMEWHAT.  THE MOST SIGNIFICANT CHANGE TO THE NEW
FORECAST IS A SLIGHT NORTHWESTWARD SHIFT OF THE 96-HOUR POINT TOWARD
THE MULTI-MODEL CONSENSUS.

THE OFFICIAL FORECAST IS LARGELY UNCHANGED AND STILL LIES NEAR THE
UPPER END OF THE GUIDANCE.  ONLY MODEST ADDITIONAL STRENGTHENING IS
FORECAST WITH KATIA EXPECTED TO MOVE OVER INCREASINGLY LESS
FAVORABLE OCEANIC CONDITIONS OVER THE NEXT SEVERAL DAYS.  IN
ADDITION...THE SHIPS GUIDANCE IS INDICATING THAT VERTICAL SHEAR
COULD BE A LITTLE HIGHER BETWEEN 24 AND 72 HOURS THAN WAS
PREVIOUSLY SHOWN...AND THIS COULD ALSO LIMIT STRENGTHENING. 
WEAKENING IS EXPECTED DURING THE LATTER PART OF THE FORECAST
PERIOD.  THE GFS IS SHOWING KATIA BECOMING EXTRATROPICAL BY DAY
5...BUT SINCE IT IS THE FASTEST OF THE MODELS IT IS PROBABLY
SHOWING THIS A LITTLE TOO SOON.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/2100Z 25.2N  63.9W  100 KT 115 MPH
 12H  06/0600Z 26.1N  64.9W  105 KT 120 MPH
 24H  06/1800Z 27.3N  66.3W  105 KT 120 MPH
 36H  07/0600Z 28.5N  67.8W  100 KT 115 MPH
 48H  07/1800Z 29.7N  69.1W  100 KT 115 MPH
 72H  08/1800Z 33.5N  70.5W   90 KT 105 MPH
 96H  09/1800Z 38.5N  66.5W   75 KT  85 MPH
120H  10/1800Z 42.0N  54.0W   65 KT  75 MPH
 
$$
FORECASTER BERG
 
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