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| #456849 (Received by flhurricane at: 4:40 PM 05.Sep.2011) TCDAT2 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 |
