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| #42251 (Received by flhurricane at: 5:03 AM 27.Aug.2005) TCDAT2 HURRICANE KATRINA DISCUSSION NUMBER 16 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SAT AUG 27 2005 THE EYE HAS BECOME CLEARLY DISCERNIBLE DURING THE PAST FEW HOURS IN GOES-12 INFRARED IMAGERY. AIRCRAFT RECONNAISSANCE INDICATES THE MINIMUM CENTRAL PRESSURE IS FALLING... MOST RECENTLY MEASURED AT 945 MB. WHILE SUCH A LOW PRESSURE IS TYPICAL OF SOME CATEGORY FOUR HURRICANES... THE MAXIMUM 700 MB FLIGHT LEVEL WINDS HAVE NOT YET EXCEEDED 104 KT WHICH CORRESPONDS TO ABOUT 95 KT AT THE SURFACE. GIVEN THE FALLING PRESSURE... AND DVORAK INTENSITY ESTIMATES RANGING FROM 100 TO 115 KT... THE ADVISORY INTENSITY WILL BE INCREASED TO 100 KT... MAKING KATRINA A CATEGORY THREE HURRICANE. THE AIRCRAFT DATA AND A FEW SURFACE OBSERVATIONS ALSO INDICATE THAT KATRINA HAS GROWN IN SIZE... WHICH PERHAPS EXPLAINS WHY THE MAXIMUM WINDS HAVE NOT YET CAUGHT UP TO THE CENTRAL PRESSURE. THE INITIAL AND FORECAST WIND RADII HAVE BEEN EXPANDED ACCORDINGLY. WSR-88D RADAR IMAGERY FROM KEY WEST... AND THE SERIES OF AIRCRAFT FIXES... INDICATE THAT KATRINA IS WOBBLING ABOUT A HEADING JUST SOUTH OF DUE WEST... SO THE LONG-ANTICIPATED TURN TO THE WEST MIGHT BE STARTING. THE DYNAMICAL MODELS ALL FORECAST A WEST-NORTHWESTWARD MOTION TO BEGIN LATER TODAY... FOLLOWED BY A GRADUAL TURN TOWARD THE NORTHWEST AND NORTH DURING THE NEXT 2-3 DAYS AS THE RIDGE TO THE NORTHWEST OF KATRINA EASES WESTWARD AND A WEAKNESS DEVELOPS OVER THE NORTHERN GULF. THE DYNAMICAL MODEL CONSENSUS FORECAST OF THE TRACK THROUGH THE GULF OF MEXICO HAD SHIFTED WESTWARD DURING THE PAST 24 HOURS OF FORECAST CYCLES. THE LATEST CONSENSUS TRACK IS ONLY SLIGHTLY WEST OF THE PREVIOUS... SO IT IS POSSIBLE THAT THE WESTWARD SHIFTING OF THE MODELS IS ENDING. THE NEW OFFICIAL FORECAST IS RIGHT ON TOP OF THE CONSENSUS TRACK AND A BIT TO THE WEST OF THE PREVIOUS ADVISORY. DUE TO THE DECREASING SPREAD IN THE MODELS... THE CONFIDENCE IN THE FORECAST TRACK IS INCREASING. KATRINA IS LOCATED WITHIN AN ATMOSPHERIC ENVIRONMENT THAT SEEMINGLY CANNOT GET MUCH MORE CONDUCIVE FOR STRENGTHENING... PRIMARILY DUE TO A VERY LARGE UPPER-LEVEL ANTICYCLONE OVER THE ENTIRE GULF OF MEXICO. NOT SURPRISINGLY... UPPER-LEVEL OUTFLOW FROM THE HURRICANE CONTINUES TO BECOME MORE ESTABLISHED. THIS WEAK WIND SHEAR ENVIRONMENT IS FORECAST BY THE DYNAMICAL MODELS TO PERSIST FOR ABOUT THE NEXT THREE DAYS UNTIL AN UPPER-LEVEL TROUGH MOVES INTO TEXAS FROM THE WEST. THEREFORE SHEAR COULD BEGIN TO INCREASE OVER THE HURRICANE NEAR THE TIME IT MAKES LANDFALL ON THE NORTHERN GULF COAST... BUT IT SEEMS THAT WILL BE TOO LATE TO PREVENT KATRINA FROM MAINTAINING MAJOR HURRICANE STATUS AT LANDFALL. THE SHIPS GUIDANCE NOW SHOWS STRENGTHENING TO 123 KT... AND THE OFFICIAL FORECAST NOW PEAKS AT 120 KT OVER THE NORTHERN GULF WITHIN THE NEXT COUPLE OF DAYS. THE 12-FOOT SEAS RADII HAVE BEEN EXPANDED BASED UPON DATA FROM NOAA BUOY 42003 AND ON SHIP DATA. FORECASTER KNABB FORECAST POSITIONS AND MAX WINDS INITIAL 27/0900Z 24.4N 84.4W 100 KT 12HR VT 27/1800Z 24.5N 85.4W 105 KT 24HR VT 28/0600Z 25.0N 87.0W 115 KT 36HR VT 28/1800Z 26.0N 88.7W 120 KT 48HR VT 29/0600Z 27.4N 89.9W 120 KT 72HR VT 30/0600Z 31.5N 90.0W 75 KT...INLAND 96HR VT 31/0600Z 36.0N 87.5W 30 KT...INLAND 120HR VT 01/0600Z 40.0N 82.0W 25 KT...EXTRATROPICAL |
