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| #455847 (Received by flhurricane at: 5:00 AM 03.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 AM AST SAT SEP 03 2011 KATIA CONTINUES TO STRUGGLE THIS MORNING WITH BURSTS OF CONVECTION FORMING AN UNSHAPELY CENTRAL DENSE OVERCAST. THE OVERALL PATTERN IS NOT WELL ORGANIZED EITHER WITH THE HURRICANE HAVING TROUBLE MAINTAINING BANDING FEATURES. SATELLITE CLASSIFICATIONS ARE A LITTLE LOWER THAN EARLIER...BUT STILL SUPPORT 65 KT ON THIS ADVISORY. IT WOULD NOT BE SURPRISING IF IT WERE A LITTLE WEAKER GIVEN THE RAGGED SATELLITE APPEARANCE. SOUTHWESTERLY SHEAR AND SOME DRY AIR CONTINUE TO PREVENT SIGNIFICANT STRENGTHENING OF THE TROPICAL CYCLONE. THE UPPER-LEVEL TROUGH TO THE NORTHWEST OF KATIA...HOWEVER...HAS BEEN WEAKENING...AND MOST OF THE GLOBAL MODELS SUGGEST THE SHEAR WILL DECREASE STARTING ON SUNDAY. THUS SLOW INTENSIFICATION IS INDICATED AT THAT TIME IN THE NHC FORECAST. AFTERWARD...VERTICAL WIND SHEAR COULD BECOME RATHER LOW BY DAY 4 AS AN UPPER-HIGH BUILDS CLOSER TO THE TROPICAL CYCLONE WHILE KATIA MOVES OVER 29C WATER TEMPERATURES. THE NHC FORECAST IS SIMILAR TO THE PREVIOUS ONE EARLY ON...NEAREST THE LGEM/SHIPS MODELS...BUT THEN IS BLENDED A LITTLE HIGHER AT THE END OF THE FORECAST PERIOD WITH THE DYNAMICAL MODEL CONSENSUS. BOTH THE HWRF AND GFDL ARE SIGNIFICANTLY STRONGER THAN THE NHC FORECAST...BUT THEY ARE PROBABLY NOT HANDLING THE MODERATE TO STRONG VERTICAL SHEAR ENVIRONMENT CORRECTLY. KATIA CONTINUES MOVING TOWARD THE NORTHWEST AT ABOUT 9 KT. ALMOST ALL OF THE GUIDANCE KEEP THIS GENERAL TRACK GOING FOR THE NEXT SEVERAL DAYS AS THE CYCLONE APPROACHES THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. THE UKMET MODEL HAS BEEN STUBBORNLY FORECASTING A MUCH STRONGER RIDGE...WHICH FORCES THE CYCLONE ON A WESTWARD COURSE CLOSER TO THE BAHAMAS. THIS WESTWARD TRACK SEEMS HIGHLY UNLIKELY DUE TO A PRONOUNCED TROUGH OVER THE WESTERN ATLANTIC OCEAN AND THE UKMET SOLUTION IS DISREGARDED FOR THIS FORECAST. OTHERWISE...THE MOST RELIABLE GUIDANCE HAS SHIFTED NORTHWARD TONIGHT...PROBABLY DUE TO THE AFOREMENTIONED TROUGH OVER THE WESTERN ATLANTIC BEING A BIT STRONGER THAN EARLIER ANTICIPATED. THE NHC FORECAST IS NEAR THE PREVIOUS ONE FOR THE FIRST COUPLE OF DAYS...THEN IS SHIFTED TO THE NORTH...BUT NOT NEARLY AS FAR AS THE MOST RECENT ECMWF/GFS/GFDL MODEL SOLUTIONS. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 19.3N 55.1W 65 KT 75 MPH 12H 03/1800Z 20.1N 56.3W 65 KT 75 MPH 24H 04/0600Z 21.1N 57.9W 65 KT 75 MPH 36H 04/1800Z 22.2N 59.7W 70 KT 80 MPH 48H 05/0600Z 23.4N 61.5W 75 KT 85 MPH 72H 06/0600Z 26.0N 64.5W 90 KT 105 MPH 96H 07/0600Z 28.5N 67.5W 100 KT 115 MPH 120H 08/0600Z 31.0N 70.0W 95 KT 110 MPH $$ FORECASTER BLAKE |
