000 WTNT42 KNHC 031452 TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 AM AST SAT SEP 03 2011 SEVERAL MICROWAVE OVERPASSES FROM EARLIER THIS MORNING INDICATED THAT KATIA IS TILTED...WITH A MID-LEVEL MICROWAVE EYE DISPLACED ABOUT 20 N MI NORTH OF THE LOW-LEVEL CENTER. FINAL T-NUMBERS ARE DOWN TO T3.5 FROM BOTH SAB AND TAFB...ALTHOUGH CI NUMBERS ARE STILL HOLDING AT 4.0. UW-CIMSS ADT ESTIMATES HAVE BEEN DECREASING AND ARE NOW T4.1. KATIA WILL BE KEPT AS A HURRICANE FOR NOW...BUT IF TRENDS CONTINUE IT COULD ONCE AGAIN WEAKEN TO A TROPICAL STORM LATER TODAY. KATIA IS BEGINNING TO MOVE AROUND THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL HIGH LOCATED OVER THE CENTRAL ATLANTIC...AND TOWARDS A DEEP-LAYER TROUGH OVER THE WESTERN ATLANTIC. WITH THE EXCEPTION OF THE UKMET...WHICH IS DISREGARDED IN THIS FORECAST...THE MODELS ARE IN GOOD AGREEMENT ON MAINTAINING A MOTION OF ABOUT 305 DEGREES AT 9 TO 10 KT FOR THE NEXT 48 HOURS. BEYOND 72 HOURS...THE TRACK FORECAST BECOMES A LITTLE MORE COMPLEX AND PARTLY DEPENDS ON HOW TROPICAL STORM LEE AND U.S. EAST COAST TROUGHING EVOLVE OVER THAT TIME. AS AN EXAMPLE...THE ECMWF DEVELOPS A DEEP-LAYER CLOSED LOW OVER THE OHIO VALLEY BY DAY 5 WHILE THE GFS HAS A SHARP TROUGH ALMOST READY TO CLOSE OFF OVER NEW YORK AND PENNSYLVANIA. DESPITE THESE DIFFERENCES...BOTH MODELS HAVE SHIFTED TO THE EAST...WITH THE GFS BEING THE FASTEST DUE TO THE MORE PROGRESSIVE FLOW. THE NHC TRACK FORECAST IS ALSO SHIFTED TO THE EAST YET STILL LIES TO THE WEST OF THOSE USUALLY RELIABLE MODELS. STRONG SOUTHERLY SHEAR IS AFFECTING KATIA AND IS LIKELY ALLOWING DRY AIR TO ERODE THE DEEP CONVECTION ON THE SOUTHERN SIDE. THIS SHEAR IS EXPECTED TO PERSIST FOR THE NEXT 24 HOURS OR SO...DURING WHICH TIME NO STRENGTHENING IS INDICATED IN THE FORECAST. THEREAFTER... THE SHIPS MODEL SHOWS THAT UPPER-LEVEL WINDS COULD BECOME MORE CONDUCIVE FOR STRENGTHENING...BUT THIS WILL ALL DEPEND ON THE LOCATION OF KATIA RELATIVE TO THE DEEP-LAYER TROUGH OR CLOSED LOW OVER THE EASTERN UNITED STATES. THE NHC INTENSITY FORECAST WILL CONTINUE TO INDICATE INTENSIFICATION BETWEEN DAYS 2 AND 4...AND IS STILL ABOVE THE INTENSITY CONSENSUS AND STATISTICAL MODELS. IT IS ADVISABLE NOT TO FOCUS ON SLIGHT FORECAST INTENSITY CHANGES NEAR THE MAJOR HURRICANE THRESHOLD OF 100 KT SINCE THERE IS VERY LITTLE DIFFERENCE BETWEEN A 95- AND 100-KT HURRICANE. BASED ON THE CURRENT FORECAST AND RECENT NHC INTENSITY ERRORS...AT THIS TIME THERE IS ROUGHLY A 50/50 CHANCE OF KATIA STILL BECOMING A MAJOR HURRICANE DURING THE NEXT 5 DAYS. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 19.6N 55.8W 65 KT 75 MPH 12H 04/0000Z 20.3N 57.0W 65 KT 75 MPH 24H 04/1200Z 21.3N 58.7W 65 KT 75 MPH 36H 05/0000Z 22.5N 60.4W 70 KT 80 MPH 48H 05/1200Z 23.7N 62.1W 75 KT 85 MPH 72H 06/1200Z 26.5N 65.0W 85 KT 100 MPH 96H 07/1200Z 29.5N 67.5W 95 KT 110 MPH 120H 08/1200Z 32.0N 69.5W 90 KT 105 MPH $$ FORECASTER BERG