940
AXPQ20 PGUM 270042
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1042 AM ChST Wed Aug 27 2025

Tropical Weather Discussion for the Western North Pacific between
the Equator and 25N from 130E to 180. The following information is
based on recent satellite imagery/data, weather observations, radar,
and meteorological analysis.

...SPECIAL FEATURES...

TROPICAL AND MONSOON DISTURBANCES...
Similar to yesterday, a surface trough/monsoon trough stretches
from 15N130E to northeast of Yap...ending near a col at 2N150E.
This end point was at EQ145E yesterday, thus the westerly winds
have helped "push" the col east-northeast today...with more of a
burst pattern also noted in these westerly winds. One needs to
always be cautious with westerly wind bursts (WWB)/westerly flow,
and it`s no surprise today that the models spin up two or there
weak systems over the next 3 to 6 days, one north of Palau, one
northwest of the Marianas, and one between Chuuk and Guam. It
remains to be seen if this occurs, but todays run of the ECENS
and GEFS support it as more ensemble members show this potential.

As for the Monsoon trough, aside from being a potential "player"
in the scenario just mentioned above, widespread cloudiness with
scattered shower and a thunderstorm or two are occurring south and
west of this feature, and this looks to continue the next few
days.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trade wind trough north of Koror at 13N135E stretches northeast
to 25N140E, but it`s mainly void of convection, aside from near
20N and points northward, where convection that`s occurring is
more a result of a TUTT cell, despite MIMIC PWATs of 2.5 to 2.8
inches. This trough looks to pass harmlessly off to the west the
next few days.

A more subtle trough east of the Marianas stretches from near
15N150E to 22N156E. Only isolated showers are thunderstorms are
occurring to you get near 20N, again due to the effects of a
nearby TUTT cell. This feature may become more convectively
active towards the weekend though as it`ll be near the Marianas
with a possible interaction with a circulation approaching from
the southeast.

Further south, a compact and subtle trough stretches from EQ158E
to near Pohnpei. Cyclic scattered to numerous showers continue to
develop near this feature with isolated thunderstorms mixed in as
well. This feature denotes the leading edge of an ITCZ with PWATs
of 2.5 to 3 inches (locally higher) common along and behind it,
helping to fuel robust convection at times with cloud top
temperatures in excess of - 80 deg. C, indicative of some very
heavy rainfall. This looks to continue the next several days as it
continues west across the region.

Finally, we have a trough from 3N160 stretching northeast as it
passes by just east of Kosrae, ending near Kwajalein. This feature
has fairly robust convection from Kosrae to south of Kwajalein,
where scattered to numerous showers and a few thunderstorms
occurring. Here too, cloud top temperatures "north" of -80 deg. C
indicate locally heavy rainfall occurring, with convection more
isolated to scattered near the northern and southern tips of the
trough. This feature will continue westward in similar convective
fashion the next few days, possibly developing a circulation along
it. Stay tuned!

TUTT...
The TUTT is in much the same place as it was yesterday, stretching
from near 25N180 to a col just north-northwest of Wake Island,
then northwest to a cell at 24N1256E. through another col at
25N146E, to a cell a 22.3N 138.7E, exiting Guam`s AOR north of
25N130E. Most of the shower and thunderstorm activity is located
along the southern through eastern flanks of the cells, and along
the southern edge of the cols where divergence boosts ascent for
at least widely-scattered shower development. The TUTT will
continue to strengthen the next few days with just minor
positional/orientation changes.

...ITCZ...
A fragmented but active ITCZ stretches basically from 158E to the
Date Line and beyond, with the most active convection centered
between 3N and 8N. This is forecast to continue as it moves west
while lifting north with time, where abundant cloud cover,
scattered to numerous showers, and embedded thunderstorms will
continue to develop.

$$

Doll