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AXPQ20 PGUM 190021
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1021 AM ChST Sun Jul 19 2026

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 buffer circulation has set up well south of Kosrae near 2S,
which has absorbed most of the energy from Invest 90W. As a
result, JTWC (the Joint Typhoon Warning Center) has downgraded
Invest 90W to a "Sub-Low" rating. It remains to be seen if 90W
will completely fizzle out or redevelop in the coming days.

Of more note is what looks to be a monsoon gyre pattern trying to
set up. The upper levels certainly reflect it with a TUTT-like
cell east-northeast of Pagan near 19N149E, and another cell near
15N179E. However, no TUTT axis is connecting them, as these lows
are flanked by an upper high west-northwest of Wake Island near
21N160E. The combination of this upper high and cell near the Date
Line is advecting abundant dry air in the easterly upper flow all
the way back to 15E, centered between 10N and 18N.

Then near the surface, you have a weak surface low just northwest
of Wake Island near 20N165E, with a few shallow showers around its
periphery. Farther south and west, a sharp trough is positioned
near 139E, connecting a broad surface low near Iwo To at 23N140E,
to what appears to be a developing weak surface low well west of
Guam near 13N139E. A surface trough extends east-southeast from
this low to what`s left of 90W near 11N154E. It then passes
through a col north of Kosrae near 9N164E, before connecting to a
broad surface circulation southeast of Majuro near 5N 175E, with
the trough crossing the Date Line near 5N180. This Majuro low is
more broad compared to yesterday as well.

We expect the patterns mentioned above to hold the next few days,
with a monsoon gyre likely setting up. It`s possible a weak
tropical circulation may develop west of the Marianas, possibly
with the two circulations near Iwo To and 13N139 being the
"breeding ground" for one or a pair of tropical disturbances to
get better organized. Also, a Monsoon trough, described below,
will likely continue south of this location, with the gyre and
Monsoon trough likely persisting through much of next week.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
As mentioned above, a monsoon trough has redeveloped and
strengthened, with the edge of said trough entering Guam`s AOR
near 10N130E. It then continues east-northeast to a broad,
potentially developing circulation located well west of Guam near
12N139E. Along and south of this trough, west-southwesterly flow
is helping focus fairly widespread shower and thunderstorm
development south of the trough axis from near Koror, through Yap,
to south-southwest of Guam and near Chuuk. Given the setup
mentioned above, this monsoon trough will likely persist the next
several days, potentially expanding north east-northeast, as
additional vorticity centers develop between 13N139E and Chuuk or
Pohnpei. Stay tuned!

$$

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