019
AXPQ20 PGUM 012355
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
955 AM ChST Tue Sep 2 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...
A surface trough extends from Invest 95W west of Guam`s AOR to
19N130E, extending northeast, ending near 24N138E. Meanwhile to
the east, a ridge axis extends south from near Iwo To, to west of
the Marianas, through Yap and Koror. In between these systems a
southwest monsoon flow is allowing for widespread shower and
thunderstorm development, mainly between 10N and 20N from 130E to
138E. These features will all continue to gradually shift west
over the next few days, as will a similar convective pattern.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A surface trough stretches from 2N143E through Guam and portions
of the CNMI, ending near Saipan. Widespread showers and a few
thunderstorms continue to develop within this feature, as has
been the case for the past several days. This feature will
continue west for the next few days in a similar convective
fashion.

To the east in the trades lies another trough that stretches from
between Chuuk and Pohnpei, extending northeast to near Taongi in
the RMI. This feature has shown less convective development over
the last day or so, but this looks to be short-lived, as a ITCZ
fragment approaching the Date Line catches up to it in a couple
days, helping to ignite more convective development as it gets an
infusion of deeper moisture.

TUTT...
A high-amplitude pattern has developed with a ridge from 15N130E
extending northeast to off the eastern Japanese coast. This has
"pinched off" the expansive TUTT that has been in place for more
than a week. The models did show this possibility, but not to this
magnitude. As a result, today`s TUTT axis was forced to
reorientate, now stretching from 25N180 southwest to just
northwest of Wake Island, to a developing cell near 17N155E, with
the rail of the TUTT ending near Saipan. Another area of high
pressure is located south of the TUTT axis, centered near 14N180.

The models shows this orientation continuing through the
remainder of the week, with a new cell forming near Wake Island,
and the developing cell at 155E drifting to near the northern CNMI
by Friday. The TUTT axis will expand west to near 17N130E by the
weekend as the ridge gets "bumped" northwest to the Sea of Japan.

Scattered to numerous showers are occurring along the southern
axis of the TUTT, generally from the Marianas northeast through
Wake Island, to the Date Line. As the TUTT gradually strengthens
this week, convection with the TUTT is expected to increase in
coverage.

...ITCZ...
The ITCZ has weakened significantly with no appreciable convection
tied to it. That said, a new ITCZ fragment will cross the Date
Line, arriving at Majuro Wednesday, and Kosrae Wednesday night, as
a trough in the flow moves through. This really signifies what
the models show this week, the lack of a cohesive ITCZ with just a
trough or two focusing convection as the move west across the
region through the weekend and into early next week.

$$

Doll