056
AXPQ20 PGUM 130121
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1121 AM ChST Mon Oct 13 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 new circulation has formed and is now dubbed Invest 96W from
JTWC, with a low rating of development during the next 24 hours.
We`ve been watching this circulation for a couple days now as it`s
been broad along a trough originally southeast of Chuuk. Now, the
circulation is still broad but not as much with visible imagery
clearly showing westerly winds south of the developing
circulation, which is currently estimated to be near 5.8N 146.8E,
or well south-southeast of Guam/west-southwest of Chuuk. It
remains possible that a new circulation may develop farther east
along the trough later in the week, but the general theme is for
a developing disturbance moving northwest towards the Marianas
later this week.

Convection and cyclonic flow around the circulation has noticeably
increased over the last 24 hours. Additionally, the GEFS and ECENS
are now in better agreement with a developing circulation passing
near Guam as it heads northwest in 48 to 72 hours, likely
bringing periods of heavy rainfall to the Marianas by the middle
of the week, especially near Guam and Rota. However, uncertainty
remains as to at what strength the system will be as it does so.
This is something that we (our office and JTWC) will keep an eye
on!

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trade-wind trough extends northwest from 96W through Yap where
it turns north and continue in a less-pronounced form to 25N138E.
Between 96W and Yap, numerous showers and isolated thunderstorms
are developing in pockets (clusters), decreasing to scattered
showers between 10N and 14N, with not much on north of there.

Another trough extends northeast from 96W though western Chuuk
State before ending near 12N157E. Fairly widespread cloud cover
with embedded showers (scattered in nature - pun intended) and a
few thunderstorms are occurring.

Finally, a trough in the trades stretches from south of Namorik in
the FSM near 3N169E through Majuro before ending near 8N173E.
Enhanced surface convergence is found along a portion of this
trough near Majuro (just east through south of there). Scattered
showers and a few thunderstorms are developing along the trough,
with these showers becoming numerous near Majuro.

The pair of troughs associated with 96W will lift off to the
northwest the next few days with an increase in convective
coverage probable. The Majuro trough will continue west the next
several days with a similar convective behavior.

TUTT...
The TUTT axis enters Guam`s AOR at 19N180 and connects to a cell
west of Wake Island at 9N157E, with the axis turning southwest
from there as it passes southeast of Guam at 10N147E before ending
near 5N142E. Numerous showers and thunderstorms are occurring
near the cells northern half with scattered showers and a few
thunderstorms found around the periphery of the circulation, and
south and east of the TUTT axis where divergence is maximized.

Today`s model runs of both the GEFS and ECMWF show an upper-level
high forming over Guam (GFS) or Rota (ECMWF) with only ~5 to 10
knots of flow at 200mb (GFS) and 250mb (ECMWF) respectively. The
models show the cell currently west of Wake Island will have moved
to 22N150E with the axis passing over Wake Island as it connects
to another cell at 19N180 by Wednesday.

...ITCZ...
The ITCZ stretches from Kosrae to Majuro, then eastward across the
Date Line. This feature will expand westward from just south of
Pohnpei to the Date Line as it gradually intensifies through the
remainder of this week, reaching from ~155E to the Date Line by
the weekend (maybe slightly further west). Convection will
increase during this time as it becomes better defined.

$$

Doll