ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM OTIS DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 8 AM PDT THU SEP 29 2005 A LARGE BURST OF CONVECTION WITH CLOUD TOPS COLDER THAN -80C DEVELOPED EARLY THIS MORNING OVER AND SOUTHWEST OF THE CENTER. A 29/0912Z AMSR-E MICROWAVE OVERPASS INDICATED A LARGE CURVED BAND THAT WRAPPED MORE THAN HALF WAY AROUND THE MID-LEVEL CIRCULATION CENTER... WITH AN EXPOSED LOW-LEVEL CENTER LOCATED NEAR THE SOUTHERN TIP OF THE CONVECTIVE BAND. DVORAK INTENSITY ESTIMATES AT 12Z WERE 45 KT FROM TAFB AND SAB... AND 35 KT FROM AFWA. SINCE THAT TIME... HOWEVER... CLOUD TOPS HAVE WARMED AND THE BANDING FEATURES HAVE BECOME LESS DISTINCT. THEREFORE... THE INTENSITY HAS ONLY BEEN INCREASED TO 40 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 305/08. AS MENTIONED IN PREVIOUS DISCUSSIONS... THE EXACT CENTER REMAINS DIFFICULT TO DETERMINE. THE AFOREMENTIONED AMSR-E OVERPASS DID DEPICT A NICE LOW-LEVEL CIRCULATION... BUT OVER THE PAST 24 HOURS THERE HAVE BEEN MULTIPLE SWIRLS GENERATED IN THE DEEP CONVECTION TO THE WEST THAT HAVE THEN ROTATED CYCLONICALLY AROUND THE MID-LEVEL CIRCULATION CENTER. THE ADVISORY POSITION IS BASED ON A BLEND OF THE MID-LEVEL AND LOW-LEVEL CENTERS NOTED IN MICROWAVE DATA... WHICH ALSO MAINTAINS CONTINUITY WITH THE PREVIOUS MOTION AND FORECAST TRACK. OTIS IS EXPECTED TO GRADUALLY MOVE WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PERIPHERY OF A LARGE MID-LEVEL SUBTROPICAL RIDGE ORIENTED EAST-WEST ACROSS NORTHERN MEXICO AND BAJA CALIFORNIA. THE WESTERN PORTION OF THE RIDGE OVER BAJA CALIFORNIA IS FORECAST BY ALL THE MODELS TO BE ERODED BY A SOUTHWARD-MOVING SHORTWAVE TROUGH AFTER 72 HOURS... WHICH SHOULD ALLOW OTIS TO TURN NORTHWARD ACROSS BAJA BY 120 HOURS. ONLY THE 29/00Z ECMWF MODEL TURNS OTIS AWAY FROM THE BAJA PENINSULA. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE PREVIOUS TRACK AND THE NHC MODEL CONSENSUS... MINUS THE ECMWF. NORTHEASTERLY UPPER-LEVEL SHEAR CONTINUES TO SLOWLY ABATE ACROSS OTIS AND THIS TREND IS FORECAST TO CONTINUE THROUGH 72 HOURS. HOWEVER... SOME MID-LEVEL SHEAR UNDERCUTTING THE IMPROVING OUTFLOW LAYER APPEARS TO BE AFFECTING THE CYCLONE AND LIKELY WILL NOT WEAKEN FOR ANOTHER 24 HOURS. BUT WITH THE IMPROVING OUTFLOW PATTERN ...WEAK VERTICAL SHEAR... AND SSTS OF 28-29C BENEATH THE STORM... AT LEAST MODEST STRENGTHENING SHOULD OCCUR UNTIL COOLER WATER IS REACHED AFTER 72 HOURS. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE SHIPS AND GFDL MODELS... WHICH BRING OTIS UP TO 63 KT AND 74 KT... RESPECTIVELY... BY 48 HOURS. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 29/1500Z 17.9N 108.2W 40 KT 12HR VT 30/0000Z 18.7N 109.2W 45 KT 24HR VT 30/1200Z 19.5N 110.5W 55 KT 36HR VT 01/0000Z 20.1N 111.3W 65 KT 48HR VT 01/1200Z 20.8N 111.9W 70 KT 72HR VT 02/1200Z 21.9N 112.5W 65 KT 96HR VT 03/1200Z 24.5N 113.5W 50 KT 120HR VT 04/1200Z 28.5N 114.0W 35 KT...INLAND OVER BAJA $$ NNNN
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Page last modified: Thursday, 29-Sep-2005 14:10:24 UTC