905
AXPQ20 PGUM 120103
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1103 AM ChST Sat Sep 12 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 weak disturbance found along the monsoon trough, Invest 90W, is
centered E of the Marianas near 12.3N 156.5E. Invest 90W is
currently sub-low, meaning development is not expected for the next
day or so. Deep convection is found to the N and to the S of the
center of 90W, with scattered showers and isolated thunderstorms
evident on latest satellite imagery. Analyses show mainly a weak,
elongated circulation along the monsoon trough. Invest 90W looks to
slowly move NNW over the next few days, with little to
no development for the next couple of days, then slow strengthening
as it continues NNW.

Another weak disturbance is found along the monsoon trough, Invest
99W, ESE of Majuro near 5.7N 176.9E. Convection has decreased
significantly with 99W since yesterday, however, the circulation
appears to have little change in intensity. A small band of
cloudiness and isolated showers is seen SW of the center, with
numerous showers and isolated thunderstorms seen to the NE, crossing
the Date Line. A weak trade-wind trough found just E of the Date
Line is helping to enhance convection in this area. As the trade-wind
trough continues W over the next couple of days, convection looks to
decrease a bit over the region. However, the circulation looks to
maintain intensity or possibly slowly strengthen over the next couple
of days as it moves NW to NNW.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
The monsoon trough enters the region near 15N130E, extending ESE to
a weak circulation centered E of Yap near 9N143E. It then turns more
toward the ENE to Invest 90W. The trough continues ESE from 90W to
Invest 99W, where it turns ENE, crossing the Date Line near 8N.
Convergence S of the trough is generating scattered showers and a
few thunderstorms S of Palau to SE of Yap. A surface trough S of the
circulation E of Yap is enhancing convergence SW of Weno, Chuuk,
resulting in scattered showers and isolated thunderstorms from just
S of Weno to near the Equator near 144E. From Weno eastward, enhanced
convergence from a weak monsoon surge is producing scattered to
numerous showers and isolated thunderstorms S of the monsoon
trough across Pohnpei and Kosrae, W of Majuro. A weak trade-wind
trough to the N near 170E is enhancing convection across Kwajalein
and Roi Namur. Only spotty showers are found with the trough E of
Majuro.

SURFACE TROUGHS...
A weak surface trough extending S from the weak circulation E of Yap
is enhancing convection SW of Weno to the Equator. This trough looks
to move very slowly ENE, maintaining its current intensity.

TRADE-WIND TROUGHS...
There is a series of three trade-wind troughs that are found N of
the monsoon trough, E of the Marianas. These three troughs are
responsible for a band of enhanced convergence from NW of Saipan,
across the northern CNMI to N of Invest 90W. The first one is found
W of the Marianas, extending N from near 15N142E to 23N142E. The
second one is seen E of the Marianas, extending N from near 16N150E
to 18N150E. The third is found N of Invest 90W, extending N from
near 15N157E to 19N150E. The band of scattered to numerous showers
and isolated thunderstorms extends E from NW of Saipan to NE of
Invest 90W. The string of troughs will continue to move W,
maintaining convection N of the monsoon trough and across the
northern CNMI.

Another weak trade-wind trough near, but just E of the Date Line is
enhancing convection to the NE of Invest 99W. This trough will
maintain intensity as it moves W, crossing the Date Line within the
next few hours.

$$

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