msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc//
subj/prognostic reasoning for typhoon 12w warning nr08//
rmks/
1. For meteorologists.
2. 12 hour summary and analysis.
   A. Typhoon (TY) 12w (Nari) has intensified significantly over
the past 12 hours due to strong poleward outflow ahead of a mid-
latitude trough to the north and toward a tropical upper tropo-
spheric trough cell to the southeast. The 14nm eye is clearly
visible in both water vapor and infrared satellite imagery.
   B. TY 12w has taken a turn toward the northwest along the
southwestern periphery of a zonally-oriented subtropical ridge
with an axis extending from the Yellow Sea eastward to the
central Pacific Ocean. The current storm position estimate is
based on 141200z satellite fixes from pgtw and rjtd and a 141200z
radar fix from Okinawa. Current intensity is based on dvorak
T-numbers of 6.0/6.0 from pgtw and rjtd, radar velocity estimates
from Okinawa, and recent AMSU intensity estimates.
3. Forecast reasoning.
   A. The forecast track for warning number 8 does not differ
significantly from the previous two warnings, except that the
tau 96 position has been removed. Forecast intensities have been
increased based recent intensification. However, the reasoning
for the forecast intensity trend remains similar to that present-
ed in the previous prognostic reasoning message.
   B. TY 12w is expected to continue rounding the western peri-
phery of the subtropical steering ridge to the northeast. Pole-
Ward outflow will remain favorable ahead of an approaching mid-
latitude trough currently analyzed over eastern China. After
the system reaches the steering ridge axis around tau 24, ver-
tical wind shear will increase and the storm will steadily
weaken as it accelerates poleward of the ridge axis. As the
system moves into the Sea of Japan, strong vertical wind shear,
passage over cooler water, and cold air advection from the west
are expected to induce a quick extratropical transition commen-
cing at tau 48 and completing by tau 72. The numerical model
guidance has shifted substantially in the most recent model runs,
and the consensus now reflects a slower poleward storm track with
landfall over south Korea around tau 72. However, poor model ini-
tialization of the small structure and high intensity of the
storm may be contributing to this recent shift in the model
trackers. This trend in the model forecasts will be closely
monitored, and a westward shift in the tau 48 and tau 72
forecast positions may be necessary in subsequent forecasts.
Forecast team: Alpha//