553
AXPQ20 PGUM 150127
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1127 AM ChST Tue Sep 15 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 developing disturbance, Invest 90W, is centered E of Tinian and
Saipan near 15.1N 150.9E, moving NW. 90W is now rated high and is
the subject of a Tropical Cyclone Formation Alert (TCFA). This means
that Invest 90W is expected to develop into a significant tropical
cyclone (tropical depression) within the next 24 hours. A distinct
Low-Level Circulation Center (LLCC) is now more evident and
indicates the system is organizing. The environment remains
conducive to strengthening and Invest 90W is expected to become a
tropical depression within the next day. Numerous showers and
isolated thunderstorms are found near the center and to the E of the
center. Convection is expected to increase as 90W progresses NW and
strengthens over the coming days.

For more information on Invest 90W and the TCFA, see bulletins
issued by the Joint Typhoon Warning Center under WMO header ABPW10
PGTW and WTPN21 PGTW.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
The monsoon trough enters the region near 13N130E, extending E
to a weak circulation centered ESE of Guam near 12N148E, turning
ENE to Invest 90W. It then turns ESE toward the northern Marshall
Islands near 10N174E, turning back to the E, crossing the Date Line
near 11N. Scattered showers and isolated thunderstorms are found S
of the trough, across northern Palau to well S of Yap, within a weak
monsoon surge and a band of convergence. Farther E, scattered to
numerous showers and a few thunderstorms are found across
northwestern Yap State. This surge is producing near-gale to gale
force gusts across this area and S to near Weno, Chuuk, along with
the convection. Scattered to numerous showers are also found with the
weak circulation ESE of Guam near the center across the Marianas. E
of Invest 90W, scattered to numerous showers are seen well N of
Pohnpei and Kosrae to W of Wake Island. Convection becomes isolated
E of 164E. The monsoon trough looks to slowly drift NW over the
eastern portion of the trough as Invest 90W tracks NW. The remainder
of the trough is expected to remain quasi-stationary. The intensity
looks to remain unchanged except near Invest 90W, where strengthening
is likely as 90W develops.

SURFACE TROUGHS...
A surface trough over the far northwestern portion of the area is
seen extending NNW from near 18N135E to end near 25N133E. Scattered
showers and isolated thunderstorms are found with this trough. The
trough is expected to exit the area, moving W of 130E during the next
24 hours.

OTHER SYSTEMS...
A band of convergence seen SW of Pohnpei is producing scattered
showers and isolated thunderstorms from SW of Pohnpei to near
Nukuoro. This band is expected to drift NW as Invest 90W progresses.

$$

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