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| #455768 (Received by flhurricane at: 10:55 PM 02.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 PM AST FRI SEP 02 2011 A SERIES OF MICROWAVE IMAGES DURING THE LATE AFTERNOON CLEARLY SHOWED THE MID-LEVEL CENTER DISPLACED TO THE NORTH OF THE LOW-LEVEL ONE. THIS MEANS THAT KATIA CONTINUES SUFFERING FROM SOUTHERLY SHEAR AND HAS NOT INTENSIFIED. THE CLOUD PATTERN IS NOT VERY IMPRESSIVE FOR A HURRICANE...BUT THE INITIAL INTENSITY IS CONSERVATIVELY KEPT AT 65 KNOTS BASED ON T-NUMBERS FROM TAFB AND SAB. THERE IS A SIGNIFICANT EXPANSION OF THE OUTFLOW IN THE WESTERN SEMICIRCLE GIVING THE FALSE IMPRESSION THAT THE SHEAR IS WEAKENING. THIS IS EXPECTED TO BE TRANSIENT SINCE WATER VAPOR IMAGES STILL SHOW THAT THE UPPER-LEVEL TROUGH CAUSING THE SHEAR IS STILL THERE...AND GLOBAL MODELS BASICALLY KEEP POSTPONING ITS WEAKENING. ACTUALLY... THE SHIPS MODEL INDICATE THAT UPPER-LEVEL WIND ENVIRONMENT WILL REMAIN HOSTILE FOR 24 TO 36 HOURS...WHILE THE ECMWF KEEPS IT HOSTILE EVEN LONGER. ON THIS BASIS...THE OFFICIAL FORECAST CALLS FOR NO CHANGE IN INTENSITY FOR ABOUT TWO DAYS AND FOR STRENGTHENING THEREAFTER. KATIA IS MOVING TOWARD THE NORTHWEST OR 305 DEGREES AT 10 KNOTS. GLOBAL MODELS UNANIMOUSLY BUILD THE SUBTROPICAL RIDGE WESTWARD AND WEAKEN THE TROUGH OVER THE WESTERN ATLANTIC. THIS FORECAST PATTERN CALLS FOR A GENERAL NORTHWEST TO WEST-NORTHWEST TRACK WITH NO SIGNIFICANT CHANGE IN SPEED THROUGH FIVE DAYS AS INDICATED IN THE NHC FORECAST. WITH THE EXCEPTION OF THE UK MODEL WHICH BUILDS A STRONGER SUBTROPICAL RIDGE THAN THE OTHER MODELS AND KEEPS KATIA ON A MORE WESTWARD TRACK...THE REST OF THE TRACK MODELS ARE IN GOOD AGREEMENT. THE OFFICIAL FORECAST IS IN THE MIDDLE OF THE GUIDANCE ENVELOPE AND IS VERY CLOSE TO THE ECMWF AND THE GFS GLOBAL MODELS. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 18.5N 54.3W 65 KT 75 MPH 12H 03/1200Z 19.5N 55.4W 65 KT 75 MPH 24H 04/0000Z 20.5N 57.0W 65 KT 75 MPH 36H 04/1200Z 21.5N 59.0W 65 KT 75 MPH 48H 05/0000Z 22.5N 60.5W 75 KT 85 MPH 72H 06/0000Z 24.5N 63.5W 85 KT 100 MPH 96H 07/0000Z 26.5N 66.5W 95 KT 110 MPH 120H 08/0000Z 28.0N 69.5W 95 KT 110 MPH $$ FORECASTER AVILA |
