000 WTNT42 KNHC 070235 TCDAT2 SUBTROPICAL STORM OTTO DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010 1100 PM AST WED OCT 06 2010 AFTER THE LAST ADVISORY WAS ISSUED...THE HURRICANE HUNTER AIRCRAFT MADE ONE MORE PASS THROUGH THE CENTER OF OTTO AND MEASURED A PEAK 1500-FT FLIGHT-LEVEL WIND OF 68 KT IN THE SOUTHEASTERN QUADRANT... CORRESPONDING TO ABOUT 54 KT AT THE SURFACE. AN SFMR WIND OF 55 KT WAS ALSO REPORTED EARLIER IN THE MISSION...AND THAT WILL BE THE INITIAL INTENSITY IN THIS ADVISORY. WATER VAPOR AND INFRARED IMAGERY SHOW THAT THE SURFACE AND UPPER-LEVEL LOW ARE ALMOST COLLOCATED...BUT RECENT AMSU DATA INDICATE THAT THE WARM CORE IN THE MID-LEVELS OF THE CIRCULATION IS STRENGTHENING. ALTHOUGH OTTO STILL LOOKS LIKE A CLASSIC SUBTROPICAL CYCLONE IN SATELLITE IMAGERY...IT APPEARS TO BE SLOWLY GAINING TROPICAL CHARACTERISTICS. VERTICAL SHEAR IS EXPECTED TO BE LIGHT FOR THE NEXT 48 HOURS OR SO...AND THE CYCLONE HAS AN OPPORTUNITY TO STRENGTHEN DURING THAT PERIOD. THE STATISTICAL INTENSITY GUIDANCE SHOWS THE MOST STRENGTHENING AND BRINGS OTTO TO AN 80-KT HURRICANE...BUT THESE MODELS PROBABLY DO NOT HANDLE TRANSITIONING SUBTROPICAL CYCLONES AS WELL AS PURE TROPICAL CYCLONES. THE OFFICIAL FORECAST LEANS CLOSER TO THE DYNAMICAL HURRICANE AND GLOBAL MODELS AND SHOWS OTTO REACHING 65 KT FROM 24 TO 48 HOURS BEFORE THE SHEAR INCREASES. GRADUAL WEAKENING IS EXPECTED THEREAFTER WITH OTTO BECOMING AN EXTRATROPICAL CYCLONE BY 96 HOURS...IF NOT SOONER. THE INITIAL MOTION IS 360/3. THE TRACK GUIDANCE REMAINS IN GENERALLY GOOD AGREEMENT...AND LITTLE CHANGE WAS REQUIRED TO THE PREVIOUS FORECAST TRACK. OTTO SHOULD MOVE LITTLE FOR THE NEXT 12 HOURS OR SO BEFORE ACCELERATING NORTHEASTWARD BETWEEN A MID-LEVEL HIGH OVER THE CENTRAL ATLANTIC AND A MID/UPPER-LEVEL TROUGH OVER THE WESTERN ATLANTIC. FORECAST POSITIONS AND MAX WINDS INITIAL 07/0300Z 23.5N 68.2W 55 KT 12HR VT 07/1200Z 23.9N 68.1W 60 KT 24HR VT 08/0000Z 24.7N 66.9W 65 KT 36HR VT 08/1200Z 26.0N 64.8W 65 KT 48HR VT 09/0000Z 27.8N 61.6W 65 KT 72HR VT 10/0000Z 32.0N 52.0W 60 KT 96HR VT 11/0000Z 37.0N 38.5W 45 KT...POST-TROP/EXTRATROP 120HR VT 12/0000Z 42.0N 27.0W 40 KT...POST-TROP/EXTRATROP $$ FORECASTER BERG