subj/prognostic reasoning for super typhoon 09w warning nr16//
rmks/
1. For meteorologists.
2. 12 hour summary and analysis.
   A. Super Typhoon (STY) 09w (Sepat) has intensified slightly over
the past 12 hours, but the eye temperature has cooled somewhat from
fixes 03 hours ago. Overall, sty 09w has maintained intensity since
15/1800z, obtaining a peak intensity between 15/1800z and 16/0000z.
The storm has tracked northwestward at nearly 08 knots along the
southwest periphery of the subtropical steering ridge over the past
12 hours and has maintained a cloud free eye.
   B. The current position is based on a tight grouping of eye
fixes from pgtw, rjtd, and knes. A 152225z SSMI image (85h) depicts
a solid eyewall and a more symmetric low level circulation than that
depicted in recent animated water vapor satellite imagery, which
depicts the eye as being slightly offset to the north within the deep
convection. Satellite-derived intensity estimates all showed 140
knots and a 152300z AMSU microwave intensity estimate of 143 knots,
which supports an initial intensity of 140 knots. Recent enhanced
infrared imagery yields a cloud-free, 17-nm diameter eye. The intense
system continues to be maintained by strong equatorward outflow that
has merged with the upper level flow (from northeast to southwest)
over the South China Sea. Some indications of a poleward outflow
channel developing exist, but good poleward outflow has yet to begin. 
3. Forecast reasoning.  
   A. The forecast philosophy for sty 09w has remained unchanged
since the previous prognostic reasoning.  
   B. Sty 09w is expected to continue to track along the southwest
periphery of the subtropical ridge to the north and east of the storm
through the forecast period. This subtropical ridge will continue to
build to the west and remain oriented southeast to northwest enabling
a northwestward track until landfall along the southeastern coast
of China prior to tau 72. The majority of the models depict this
scenario with the exception of the EGRR and the TCLAPS trackers. Egrr
is a western outlier and it continues to apparently lose the storm
circulation and merge the storm within the broad troughing over the
South China Sea. TCLAPS is a slight eastward outlier and tracks the
storm over northern Taiwan. Favorable upper level outflow and high
sea surface temperatures support the maintaining of the storms
current intensity through tau 24. After this time, sty 09w should
weaken slightly before striking Taiwan, due to land interaction and
somewhat lower sea surface temperatures/ocean heat content. The storm
will continue to weaken after landfall in southern Taiwan due to land
interaction with Taiwan and the coast of China.     
   C. All extended models depict landfall in China just prior to or
just after tau 72. The storm will weaken substantially after tau 72
as the low level circulation tracks into southeastern China.
Dissipation over land is expected by tau 96.
Forecast team: Bravo//