613
AXPQ20 PGUM 170228
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1228 PM ChST Sun Aug 17 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...
Invest 90W is located near 7N158E (near Pohnpei) as an open wave
trough. This trough is rather deep and can be seen up to 500 MB.
This feature is producing scattered to numerous showers with isolated
thunderstorms. Currently, this feature is in a state of decay. As
the day progresses, this feature is expected to further spread out
and decay. This decaying phase does not look to last though. Models
indicate once this feature gets closer to Chuuk around Monday
morning, conditions may become more favorable for development.

...OTHER WEATHER SYSTEMS...

MONSOON-LIKE TROUGH...
A monsoon-like trough enters the region near 23N130E and extend
eastward to 24N136E (west-southwest of Iwo To). This feature is
producing overcast skies with numerous to widespread showers.
Scattered thunderstorms have been detected near the northern tip of
this feature near 24N135E. This trough is expected to move in a
northwest direction over the next few days and maintain current
intensities.

TUTT...
The TUTT enters the region near 25N163E (north of Wake Island) and
extend south into a cell near 15N163E, then continues to snake its
way south into a col near 10N163E. This feature is not producing much
in the way of convection, it is providing much needed ventilation
for other features in the region.

A TUTT cell is located near 25N133E and is the northern anchor point
for a second TUTT. This TUTT extend southeastward towards Guam. This
trough and cell are providing aid to the monsoon-like trough and is
expected to move with that feature over the coming days


TRADE-WIND TROUGHS...
There are two notable trade-wind troughs in the region. The first is
located in northern CNMI near 17N144E (west of Alamagan) and extend
northeastward to 25N149E (between Iwo To and Minami Torishima).
Convection associated with this feature is along the eastern side of
the trough axis. The second trough is located near 21N155E (south of
Minami Torishima) and extend southwestward to 16N154E. Showers with
both of these troughs are expected to be isolated to scattered. These
troughs are expected to be quasi-stationary and maintain isolated to
scattered showers.

OTHER SYSTEMS...

...ITCZ...
There are three notable features within two fragments of the ITCZ,
the first is a broad surface trough along the leading edge of the
western fragment, the second is Invest 90W (more on that above), and
the third is the eastern fragment. These fragments are not likely to
fill in and become one, but is more likely that the western fragment
will out run the eastern fragment propagates westward.

The broad trough that is embedded with the western fragment is
located in eastern Yap and western Chuuk states with the axis near
11N145E extending south to EQ144E. Convection associated with this
feature extend 150 NM on either side of the trough axis. Expect to
see numerous to widespread showers and isolated thunderstorms.
Satellite imagery shows this feature producing multiple cells as it
moves westward. Yap Proper can expect to see this feature later
tonight and Palau can see this tomorrow. The intensity is expected to
remain stable as this feature moves westward.

The eastern fragment is more of a true ITCZ fragment and is producing
widespread showers and isolated thunderstorms, between 5N and 12N,
and from 170E to the Date Line (over Majuro). This fragment is
expected to propagate westward with varying intensities as these
cells form and decay.

$$

Bowsher