Subtropical Storm OTTO

ZCZC MIATCDAT2 ALL
TTAA00 KNHC DDHHMM
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
 
NNNN