wdpn31 pgtw 010300
msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc//
subj/prognostic reasoning for typhoon 10w warning nr14//
rmks/
1. For meteorologists.
2. 12 hour summary and analysis.
   A. Typhoon (TY) 10w (Fitow) has tracked consistently west-
northwestward at 08 kts over the past 12 hours, under the
influence of the subtropical ridge to its northeast. However,
the convective structure of the system has changed considerably
during the same period. Animated water vapor imagery and an
SSMI microwave vapor image from 31/2013z indicate that intrusion
of drier, subsident air from a tropical upper tropospheric trough
(tutt) temporarily dissipated nearly all deep convection around
the core of the storm. However, the storm has maintained a strong
low level signature over warm water, and upper level outflow has
improved to both the southwest and northeast of the system,
allowing deep convection to redevelop near the storm center.
   B. Dvorak satellite intensity estimates from rjtd have remained
at 4.5, while those from pgtw and knes have risen to 4.0/4.0 due
to the increase in deep convection. The initial intensity is held
at 70 kts for this warning based on these Dvorak estimates. Water
recent vapor imagery shows that an extension of the TUTT to the
northeast of TY 10w is improving poleward outflow and subtropical
ridging to the west is beginning to enhance equatorward outflow,
establishing a much more favorable outflow regime for TY 10w.
3. Forecast reasoning.
   A. The forecast track speed has been reduced slightly based
on a weaker anticipated steering environment. The intensity
forecast remains largely unchanged since the previous prog-
nostic reasoning.
   B. TY 10w is expected to continue tracking generally westward
through tau 72 along the periphery of a subtropical ridge exten-
sion to the north of the storm. A developing ridge to the south
and east of Japan is expected to provide a secondary steering
influence, inducing a slight slowdown in forward track speed and
a slight dip southward between tau 12 and tau 36. As the second-
Ary steering ridge weakens, the primary subtropical steering
ridge will provide an increasing northward component to storm
motion between tau 36 and tau 72. The available numerical model
guidance is in fair agreement, however most models depict a
slightly stronger secondary steering ridge and a consequently
more significant southwestward dip in the storm track than
reflected in the current forecast. Improving poleward and
equatorward outflow will allow the system to intensify and
should facilitate improvements in convective structure. However,
because remnant dry air will continue to affect the system and
total ocean heat content is marginal despite high sea surface
temperatures, the system is expected to intensify at a less
than climatological rate through tau 72.
  C. An approaching mid-latitude trough will cause an eastward
retreat of the subtropical ridge east of Japan, inducing a more
poleward track in the extended period. TY 10w should reach its
peak intensity near tau 96 as the midlatitude trough enhances
poleward outflow. After tau 96, the storm is expected to weaken
as it encounters increased westerly vertical wind shear associ-
ated with strong upper level winds over Japan.
Forecast team: Delta//