ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NORBERT DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008 800 PM PDT SUN OCT 05 2008 DEEP CONVECTION HAS BEEN WAXING AND WANING AROUND THE LOW-LEVEL CIRCULATION CENTER THIS AFTERNOON AND EVENING...BUT THE OVERALL TREND HAS BEEN FOR IMPROVED ORGANIZATION. DVORAK SATELLITE INTENSITY ESTIMATES ARE T3.0/45 KT FROM BOTH TAFB AND SAB. HOWEVER...3-HR AVERAGE ODT/ADT ESTIMATES HAVE BEEN T3.8 TO T3.9. ALSO...THERE WAS A 05/2317Z AMSU INTENSITY ESTIMATE OF 55 KT. THEREFORE...THE INITIAL INTENSITY HAS BEEN INCREASED TO 55 KT. THE INITIAL MOTION ESTIMATE IS 270/07. THE INITIAL POSITION WAS ADJUSTED SLIGHTLY TO THE SOUTH OR LEFT OF THE PREVIOUS TRACK BASED ON A 05/2022Z AMSR OVERPASS...WHICH REVEALED A TIGHT LOW-LEVEL CIRCULATION CENTER IN THE 37 GHZ CHANNEL ALONG 14N LATITUDE. OTHER THAN THE SLIGHT SOUTHWARD RELOCATION...THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR PHILOSOPHY. FOR THE NEXT 96 HOURS...NORBERT IS EXPECTED TO GRADUALLY MOVE WEST-NORTHWESTWARD AND THEN TURN NORTHWESTWARD AROUND THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE SITUATED TO THE NORTH OF THE CYCLONE. AFTER THAT...A MID-LEVEL SHORTWAVE TROUGH IS FORECAST TO DROP SOUTHWARD ALONG THE U.S. WEST COAST AND INTO THE U.S. DESERT SOUTHWEST BY 120 HOURS...WHICH SHOULD WEAKEN THE RIDGE AND ALLOW NORBERT TO TURN MORE TOWARD THE NORTH. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND IS ALSO SIMILAR TO BUT FASTER THAN THE NHC MODEL CONSENSUS...TVCN. THE MODERATE EASTERLY SHEAR THAT HAS BEEN PLAGUING NORBERT FOR MANY DAYS NOW IS EXPECTED TO DECREASE SLIGHTLY AND SHIFT AROUND FROM THE SOUTHEAST OVER THE NEXT 72 HOURS. ALTHOUGH THE CYCLONE IS FORECAST TO REMAIN OVER 28C AND WARMER SSTS DURING THIS TIME...THE MID-LEVEL ENVIRONMENT IS FORECAST TO GRADUALLY BECOME LESS MOIST. THE RESULT IS THAT ONLY SLOW STRENGTHENING INTO A CATEGORY 1 OR 2 HURRICANE IS EXPECTED. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND THE SHIPS INTENSITY MODEL...BUT IS MUCH LOWER THAN THE HOT-TO-TROT HWRF MODEL...WHICH MAKES NORBERT A 119-KT CATEGORY 4 HURRICANE IN 2-3 DAYS. IN CONTRAST...THE USUALLY ROBUST GFDL MODEL BARELY BRINGS THE CYCLONE UP TO 70 KT IN 48 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 06/0300Z 14.1N 103.7W 55 KT 12HR VT 06/1200Z 14.3N 104.6W 60 KT 24HR VT 07/0000Z 14.7N 105.7W 65 KT 36HR VT 07/1200Z 15.1N 107.0W 70 KT 48HR VT 08/0000Z 15.7N 108.3W 75 KT 72HR VT 09/0000Z 17.3N 110.5W 80 KT 96HR VT 10/0000Z 19.5N 112.5W 75 KT 120HR VT 11/0000Z 23.0N 113.5W 65 KT $$ FORECASTER STEWART NNNN
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Page last modified: Tuesday, 21-Apr-2009 12:09:45 UTC