811
AXPQ20 PGUM 210102
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1102 AM ChST Mon Sep 21 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...
The Joint Typhoon Warning Center designated Invest 91W this morning.
Invest 91W is currently located near 11N145E, or just south of Guam.
91W was initially rated sub-low, but has been upgraded to low. This
means that development into a signicant cyclone is not expected over
the next 24 hours, but will be possible over the next few days. 91W
resides on the northern edge of the monsoon trough. It remains
convectively devoid on the northern half of the system, and very
active on the south side. Widespread showers and isolated
thunderstorms are seen where the tropical disturbance and the monsoon
trough meet. Invest 91W will slowly move northwest over the coming
days.

For more information on Invest 91W, see bulletins issued by JTWC
under WMO header ABPW10 PGTW.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
The monsoon trough enters the region at 12N130E and extends eastward
into the tropical disturbance Invest 91W at 11N145E. The monsoon
trough extends further east until it reaches a col at 14N152E.
Numerous to widespread showers and isolated to scattered
thunderstorms are seen along the monsoon trough. Very heavy rainfall
has impacted Yap this morning. The monsoon trough looks to re-orient
itself over the coming days as Invest 91W develops and moves to the
northwest. This may initially shift the heavy showers towards Palau
over the next couple of days before shifting to the northwest.

SURFACE TROUGHS...
A surface trough picks up east of the col at 14N152E and extends
eastward to 14N170E where it intersects a circulation. The trough
continues east-southeast where it runs into col that is north of
another circulation at 4N175E. This trough is monsoon-like with a
single col seperating it from the monsoon trough. Scattered to
numerous showers and isolated thunderstorms are seen along the
western portion of the trough south of the col at 14N152E where a
weak circulation may be developing. Between 160E and 170E partly
cloudy skies and isolated showers are observed. Near 170E scattered
to numerous showers and isolated thunderstorms are seen near the
circulations at 14N170E and 4N175E. This feature looks to remain
near-stationary over the coming days.

A surface trough extends north of the weak circulation at 14N170E to
25N167E. Scattered to numerous showers and isolated thunderstorms
are seen along the trough. Some of these showers are being enhanced
by a weak circulation near 18N166E or just south of Wake Island.
This trough will slowly move westward over the coming days.

OTHER SYSTEMS...
A weak circulation near 18N166E or just south of Wake Island is
producing scattered showers and isolated thunderstorms near a surface
trough to the east and a TUTT to the north. This circulation looks
to slowly move southwest before being abosrbed by the surface trough
to the east in a couple of days.

TUTT... A TUTT enters the region at 25N170E and extends southwest to
15N150E. Little shower activity is seen along the TUTT, but some
enhancement of showers near the circulation near Wake Island is being
caused by the TUTT. The TUTT will shift westward and intensify over
the coming days.

$$

Williams