msgid/genadmin/navpacmetoccen Pearl Harbor hi/jtwc//
subj/prognostic reasoning for tropical depression 13w warning nr04//
rmks/
1. For meteorologists.
2. 12 hour summary and analysis.
   A. Tropical Storm (TS) 13w has been slow to organize, due to a 
small TUTT cell to its north which has suppressed convection
over the northern semi-Circle of the low level circulation center 
(LLCC). The storm has been slowly tracking westward as it continues
to consolidate. An upper level anticyclone to the east of the system
is providing excellent equatorward outflow. 
   B. The initial intensity for ts 13w is 35 kts, based on dvorak
estimates of 3.0 from pgtw and knes and 2.0 from rjtd. The llcc
is still partially exposed in multispectral imagery, but a 152307z
SSMI/S microwave pass indicates excellent convective banding on
the southern periphery and increased banding in the northeast
quadrant that is beginning to wrap toward the LLCC.
3. Forecast reasoning.
   A. The consensus track has shifted slightly southwest as more 
members have been added, and thus the official forecast has been 
shifted accordingly for the past two warnings. The intensity at 
Taus 48 and 72 has also increased, which will be further discussed
below. 
   B. Ts 13w will be steered northwestward along the monsoon trough
axis under the influence of the subtropical ridge to the northeast. 
The TUTT cell north of the system will weaken and begin to retreat
to the north. As the storm moves away from this negative influence, 
rapid intensification is likely, especially if the storm can hook 
up with a venting mechanism, such as the TUTT to its east. In fact, 
the intensity at Taus 48 and 72 may have to be further adjusted 
upward. The dynamic models are in general agreement through tau 72, 
when the storm is south of the ridge axis 
    c. The models are in poor agreement in the extended period, and
thus a large amount of uncertainty exists. The ECMWF and nogaps
models indicate that the storm will be picked up by a deep midlatitude
trough and accelerated into the midlatitude westerlies after tau 72.
GFS is also depicting a deep midlatitude trough, but loses the tracker,
and does not depict a recurvature. The official forecast track is
based off the consensus and favors recurvature (but slower than the
NOGAPS and ECMWF depictions). As the storm recurves, it will encounter 
the midlatitude baroclinic zone and begin to transition to an 
extratropical system. The models indicate a rapid transition, with 
the system becoming completely extratropical just after tau 96 over
the korean peninsula. In an alternate scenario, if ts 13w is not picked
up by the midlatitude trough, it could undergo a slower recurvature
around the subtropical ridge axis.
Transition. 
Forecast team: Charlie//