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AXPQ20 PGUM 260025
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1025 AM ChST Tue Aug 26 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...

A westerly wind flow with localized wind bursts is evident from
the equator to about 9N and from 130E to 140E before diving
southeast through a col to the equator near 145E. Modest
convergence along this feature is leading to a fair amount of
cloud cover and widely-scattered showers, with an occasional
thunderstorm also occurring from time to time. This will continue
to be the case for the next several days.

Meanwhile, a barely-recognizale small circulation is seen near
6.4N 150.4E. Little than shallow cumulus are developing. The GFS
and ECMWF maintain the WWB through day 4, with the GFS trying to
take the Chuuk circulation WNW and eventually organizing it some
as it nears 130. The Euro doesn`t do this which has outperformed
the GFS recently. Thus, while we don`t expect any circulation to
organize, the WWB will persist for at least the next few days with
little fanfare aside from spotty convection within it.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A pronounced surface trough in the trades extends from EQ150E
through a col near 5N145E, extending to northeast of Yap at
11N140E, before flattening out as it extends west-northwest to
near 14N130E. This feature bisects a weak WWB (westerly wind
burst) to its south and west from trade flow to it`s north and
east. Excellent convergence along it is leading to pockets of
convection, mainly north of 10N between 130E and 140E where good
divergence on the back edge of a TUTT is providing added ascent.
This trough looks to remain qusai- stationary the next few days.

To its north is a trough west of the Marianas stretching from
near 12N138E to the edge of a col east of Minami Torishima at
24N147E. Here too convection is getting a boost from a TUTT
interaction between 12N and 21N and from 130E to 147E. This
surface trough looks to make slow headway to the west, staying
convectively active as the TUTT axis remains the same and
strengthens over the coming days, keeping both features and their
interaction convectively active.

Finally, to it`s southeast is a long trough that resembles the
radar image of a long bow echo (or boomerang), as it stretches
from EQ169E northwestward to between Kosrae and Kwajalein, to
northeast and then north of Pohnpei where it starts to arc back to
the northeast, ending near (just west of) Wake Island. A fair
amount of cloud cover and widely-scattered showers with a few
embedded thunderstorms continue to occur along and behind this
feature, which looks to remain the case as it heads west the next
few days, aided by enhanced surface convergence between 5N and 10N
as it denotes the leading edge of an ITCZ, and again north of 15N
where increased ascent from the TUTT boosts convective coverage.

TUTT...
Speaking of the much-talked-about TUTT, it stretches from a cell
just north of 25N at 160E to a developing cell at 21N150E, then
westward to a cell well west of the northernmost CNMI at 21N139E,
exiting Guam`s AOR at 25N130E. Additionally, an upper trough
extends south from the cell near 25N160E to just west of Wake
Island ending at a col just west of Kwajalein.

The models show the TUTT cells and axis staying convectively
active the next several days both near the cells and south of the
axis connecting them where increased ascent is found. In general,
the axis will "waggle" (like your putter in golf) between 21N and
24N while stretching and strengthening to extend from beyond 130E,
eastward to beyond the Date Line by F84 (day 3.5), with it seen
continuing beyond that. Thus look for convection to get a boost
with any surface troughs heading west along it`s (the TUTT)
southern axis due to the aforementioned ascent, and near the
cells themselves. In these regions, at least scattered showers
and isolated thunderstorms (locally higher) can be expected to
occur.

...ITCZ...
The ITCZ is found between 2N and 10N up to the northwest-
orientated (negative tilt portion) of the surface trough mentioned
above. The GFS GDI indices suggest the ITCZ will strengthen as it
lifts north and east to between 6N and 13N over the next F84 (3.5
days), before it weakens by next weekend. Trade convergence and
deeper moisture profiles will continue to foster convective
development as it does so, as one would suspect.

$$

Doll