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| #42159 (Received by flhurricane at: 5:00 PM 26.Aug.2005) TCDAT2 HURRICANE KATRINA DISCUSSION NUMBER 14 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT FRI AUG 26 2005 MOST RECENT REPORTS FROM AN AIR FORCE HURRICANE HUNTER AIRCRAFT INDICATE THE CENTRAL PRESSURE HAS DROPPED TO 965 MB...BUT THE FLIGHT-LEVEL WINDS HAVE ONLY INCREASED TO 94 KT AT 700 MB...WHICH IS ABOUT AN 85-KT SURFACE WIND. A 1701Z DROPSONDE IN THE NORTHEAST QUADRANT REPORTED 85 KT SURFACE WINDS. THEREFORE...THE INITIAL INTENSITY IS HELD AT 85 KT FOR THIS ADVISORY...EVEN THOUGH THE CENTRAL PRESSURE SUPPORTS ABOUT 95-KT SURFACE WINDS. THE EYEWALL IN THE NORTHWEST QUADRANT HAS REMAINED OPEN...PROBABLY DUE TO DRY AIR ENTRAINMENT...AND THIS MAY PARTLY EXPLAIN THE DIFFERENCE BETWEEN THE OBSERVED WINDS AND WHAT THE CENTRAL PRESSURE TYPICALLY SUPPORTS. THE INITIAL MOTION IS WEST-SOUTHWESTWARD...OR 255 DEGRESS...AT 07 KT. KATRINA REMAINS CAUGHT BETWEEN THE NORTHEASTERLY FLOW ON THE WEST SIDE OF AN INVERTED TROUGH OVER THE WESTERN CARIBBEAN SEA AND THE NORTHEASTERLY FLOW IN THE SOUTHEAST QUADRANT OF THE SUBTROPICAL RIDGE LOCATED TO THE NORTH AND NORTHWEST OF KATRINA. BOTH THE RIDGE AND TROUGH ARE FORECAST TO SLOWLY WEAKEN OVER THE NEXT 12-24 HOURS ...WHICH ALLOW THE HURRICANE TO TURN MORE WESTWARD...AND MOST OF THE NHC MODEL GUIDANCE AGREES ON THAT SCENARIO. AFTER 24 HOURS... THE MODELS ARE IN GENERAL AGREEMENT ON A SHORTWAVE TROUGH CURRENTLY OVER THE NORTHERN AND CENTRAL PLAINS STATES TO GRADUALLY DIG SOUTHEASTWARD TOWARD THE CENTRAL AND WESTERN GULF OF MEXICO AND ERODE THE RIDGE...WHICH ALLOWS KATRINA TO MOVE NORTHWARD BY 72 HOURS. AS A RESULT...THE MODELS HAVE SHIFTED SIGNIFICANTLY WESTWARD AND ARE NOW IN BETTER AGREEMENT. THIS HAS RESULTED IN THE OFFICIAL FORECAST TRACK BEING SHIFTED ABOUT 150 NMI WEST OF THE PREVIOUS TRACK...ON THE EAST SIDE OF THE GUIDANCE ENVELOPE. HOWEVER... PROJECTED LANDFALL IS STILL ABOUT 72 HOURS AWAY...SO FURTHER MODIFICATIONS IN THE FORECAST TRACK ARE POSSIBLE. KATRINA IS EXPECTED TO BE MOVING OVER THE GULF LOOP CURRENT AFTER 36 HOURS...WHICH WHEN COMBINED WITH DECREASING VERTICAL SHEAR...SHOULD ALLOW THE HURRICANE TO REACH CATEGORY FOUR STATUS BEFORE LANDFALL OCCURS. THIS IS CONSISTENT WITH THE SHIPS AND GFDL MODELS...WHICH BRING KATRINA UP TO 118 KT. THE FSU SUPERENSEMBLE MODEL IS MORE ROBUST AND BRINGS KATRINA UP TO 129 KT JUST BEFORE LANDFALL. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 26/2100Z 24.8N 82.9W 85 KT 12HR VT 27/0600Z 24.9N 83.9W 90 KT 24HR VT 27/1800Z 25.2N 85.1W 95 KT 36HR VT 28/0600Z 25.8N 86.4W 100 KT 48HR VT 28/1800Z 26.9N 87.7W 105 KT 72HR VT 29/1800Z 30.0N 88.5W 115 KT 96HR VT 30/1800Z 35.0N 86.5W 35 KT...INLAND 120HR VT 31/1800Z 40.5N 79.0W 25 KT...DISSIPATING INLAND |
