ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NORBERT DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008 800 PM PDT SAT OCT 04 2008 DEEP CONVECTION HAS INCREASED AND BECOME BETTER ORGANIZED AROUND THE LOW-LEVEL CENTER...AND THE DEPRESSION HAS STRENGTHENED INTO TROPICAL STORM NORBERT. THE INITIAL INTENSITY OF 35 KT IS BASED ON A DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT FORM TAFB...AND A 04/1652Z ASCAT OVERPASS THAT CAME IN AFTER THE 21Z ADVISORY WAS ISSUED...WHICH SHOWED SEVERAL 30- TO 34-KT WIND VECTORS IN THE NORTHWEST QUADRANT. SINCE THAT THE TIME OF THE ASCAT OVERPASS... HOWEVER...THE CONVECTIVE ORGANIZATION OF THE SYSTEM HAS IMPROVED. THE INITIAL MOTION ESTIMATE IS 280/05. AVAILABLE MODEL GUIDANCE IS IN GOOD AGREEMENT ABOUT A SLOW WESTWARD TO WEST-NORTHWESTWARD MOTION THROUGH 96 HOURS AS NORBERT MOVES AROUND THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE FORECAST TO BUILD WESTWARD TO THE NORTH OF THE CYCLONE. BY 120 HOURS...A SLOW TURN TOWARD THE NORTHWEST IS EXPECTED AS A WEAK MID-LEVEL TROUGH IS FORECAST TO DIG SOUTHWARD ALONG THE CALIFORNIA COAST AND ERODE THE WESTERN PORTION OF THE MID-LEVEL RIDGE. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE PREVIOUS TRACK AND IS SLIGHTLY NORTH OF THE NHC MODEL CONSENSUS. MODERATE VERTICAL SHEAR IS FORECAST TO WEAKEN THROUGH 72 HOURS AS NORBERT REMAINS OVER SSTS GREATER THAN 28C. ALSO...AS NORBERT MOVES FARTHER WEST...THE NEGATIVE EFFECTS OF DRY EASTERLY DOWNSLOPE AIR COMING FROM THE GULF OF TEHUANTEPEC SHOULD BE REDUCED. THEREFORE... GRADUAL STRENGTHENING IS FORECAST SIMILAR TO THE SHIPS AND ICON INTENSITY MODELS. IT SHOULD BE NOTED THAT THE HWRF MODEL MAKES NORBERT A 102-KT MAJOR HURRICANE ON DAY 4. HOWEVER...THIS SCENARIO IS BEING DISCOUNTED AT THIS TIME DUE TO VERTICAL WIND SHEAR EXPECTED TO INCREASE TO MORE THAN 20 KT AFTER 72 HOURS. FORECAST POSITIONS AND MAX WINDS INITIAL 05/0300Z 14.2N 100.9W 35 KT 12HR VT 05/1200Z 14.4N 101.8W 40 KT 24HR VT 06/0000Z 14.7N 103.0W 45 KT 36HR VT 06/1200Z 15.0N 104.0W 50 KT 48HR VT 07/0000Z 15.4N 105.3W 55 KT 72HR VT 08/0000Z 16.0N 107.0W 65 KT 96HR VT 09/0000Z 17.0N 109.5W 65 KT 120HR VT 10/0000Z 18.5N 111.5W 65 KT $$ FORECASTER STEWART NNNN
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