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| #42309 (Received by flhurricane at: 10:52 AM 27.Aug.2005) TCDAT2 HURRICANE KATRINA DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 10 AM CDT SAT AUG 27 2005 REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT THE CENTRAL PRESSURE OF KATRINA DROPPED TO 940 MB AT 0932Z. SINCE THEN...THE HURRICANE HAS STARTED A CONCENTRIC EYEWALL CYCLE...WITH A FILLING OF THE EYE AND WARMING OF THE CLOUD TOPS IN SATELLITE IMAGERY. THE INITIAL INTENSITY REMAINS AT 100 KT BASED MAINLY ON SATELLITE INTENSITY ESTIMATES OF 102 KT FROM TAFB AND AFWA...AND 115 KT FROM SAB. IT SHOULD BE NOTED THAT THE MAXIMUM FLIGHT-LEVEL WINDS REPORTED BY AIRCRAFT SO FAR ARE 106 KT...WHICH ARE LOWER THAN WOULD NORMALLY BE EXPECTED FOR A 940 MB HURRICANE. THE INITIAL MOTION IS NOW 275/6. KATRINA IS SOUTH OF A DEEP-LAYER RIDGE OVER THE NORTHERN GULF COAST. THIS RIDGE IS FORECAST TO WEAKEN AS A STRONG DEEP-LAYER TROUGH DEVELOPS OVER THE CENTRAL UNITED STATES...AND A NEW DEEP-LAYER RIDGE FORMS OVER THE FLORIDA PENINSULA AND THE ADJACENT ATLANTIC. THIS PATTERN CHANGE SHOULD CAUSE KATRINA TO TURN NORTHWARD DURING THE NEXT 72 HR AND MAKE LANDFALL OVER THE NORTHERN GULF COAST. ALL TRACK GUIDANCE AGREES ON THIS SCENARIO...ALTHOUGH THERE REMAINS SOME SPREAD... PARTICULARLY FROM THE NOGAPS AND GFDN MODELS WHICH CALL FOR LANDFALL NEAR MORGAN CITY AND INTRACOASTAL CITY LOUISIANA RESPECTIVELY. THE OTHER GUIDANCE IS CLUSTERED WITH LANDFALL BETWEEN GRAND ISLE LOUISIANA AND PENSACOLA FLORIDA. THE OFFICIAL FORECAST REMAINS CLOSE TO THE MODEL CONSENSUS...CALLING FOR LANDFALL IN SOUTHEASTERN LOUISIANA IN 48-60 HR. THE NEW TRACK IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE. KATRINA SHOULD STRENGTHEN SLOWLY FOR THE FIRST 12 HR OR SO AS THE CONCENTRIC EYEWALL COMPLETES AND SOME RESIDUAL NORTHERLY SHEAR AFFECTS THE STORM. AFTER THAT...IT SHOULD STRENGTHEN IN A LIGHT SHEAR ENVIRONMENT OVER VERY WARM WATER. THE INTENSITY FORECAST CALLS FOR THE HURRICANE TO REACH 125 KT IN 48 HR AS A COMPROMISE BETWEEN THE 120 KT GFDL...THE 126 KT GFDN...THE 127 KT SHIPS...AND THE 132 KT FSU SUPERENSEMBLE MODELS. HOWEVER...IT IS NOT OUT OF THE QUESTION THAT KATRINA COULD REACH CATEGORY 5 STATUS AT SOME POINT BEFORE LANDFALL. THERE IS A POSSIBILITY THAT SOUTHERLY OR SOUTHWESTERLY SHEAR COULD AFFECT KATRINA STARTING AT 48 HR...AND AS ALWAYS HAPPENS IN HURRICANE OF THIS INTENSITY ADDITIONAL CONCENTRIC EYEWALL CYCLES COULD OCCUR. THE NEW FORECAST TRACK AND WIND RADII REQUIRE A HURRICANE WATCH FOR PORTIONS OF SOUTHEASTERN LOUISIANA AT THIS TIME...INCLUDING METROPOLITAN NEW ORLEANS. THIS WATCH WILL LIKELY NEED TO BE EXTENDED ALONG THE COAST LATER TODAY OR TONIGHT. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 27/1500Z 24.5N 85.0W 100 KT 12HR VT 28/0000Z 24.6N 86.0W 105 KT 24HR VT 28/1200Z 25.3N 87.6W 115 KT 36HR VT 29/0000Z 26.7N 89.0W 120 KT 48HR VT 29/1200Z 28.6N 89.9W 125 KT 72HR VT 30/1200Z 33.0N 89.5W 60 KT...INLAND 96HR VT 31/1200Z 37.5N 86.0W 30 KT...INLAND 120HR VT 01/1200Z 41.5N 80.0W 25 KT...EXTRATROPICAL |
