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Tropical Weather Discussion...UPDATED
National Weather Service Tiyan GU
810 PM ChST Tue Oct 7 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...

Updated for Tropical Cyclone Formation Alert on Invest 95W.

TROPICAL AND MONSOON DISTURBANCES...
Invest 95W is located near 16N143E and is now the subject of a
Tropical Cyclone Formation Alert (TCFA), meaning significant
tropical cyclone development is likely within 24 hours. This
system is about 200 miles northwest of Guam and 190 miles west-
northwest of Saipan. Maximum sustained winds are around 18 to 23
knots, and 95W is showing signs of becoming better organized with
deep convection building along the southwest and northern sectors.
Model guidance indicates 95W will continue moving north-
northwestward, away from the Marianas, and continuing to develop
over the next 48 hours, although maintaining a somewhat
asymmetrical wind field, with stronger winds on the eastern
sector.

Extending southwest to northeast, a monsoon tough stretches from
8N130E to just northwest of Koror and Yap, to west-northwest of
Guam at 13N140, passing through Saipan and ending just northeast
of there at 18N147E. Southwesterly winds of 10 to 20 knots are
developing along and south of this trough, fostering scattered to
locally numerous shower development near Koror, with a few
thunderstorms mixed in as well. Another arc of convection
stretches from north of Yap to east central Yap State and then
northward across Guam and the southern half of the CNMI. This
trough, and it`s associated convection, will continue to lift
north and west over the next few days.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trade-wind trough bisects Chuuk and Pohnpei, stretching from
near Nukuoro at 4N155E through Ujelang before ending just
northwest of Bikini Atoll at 12N165E. Scattered showers are
developing with this feature, mainly along the northern half.
Little increase in convection is expected over the next few days
as this trough heads west.

Another trough is located from 15N163E to north of Wake Island at
24N166E. Similar to the trough to the south, scattered showers are
developing with satellite imagery suggesting it`s getting a boost in
lift from an approaching upper trough, with a few thunderstorms
developing as well due to stronger lift and mid-level lapse rates.
This  portion of the surface trough looks to get displaced from the
upper trough in a few days, with a potential decrease in convection
with the surface feature.

TUTT...
An upper-trough associated with a mid-latitude cyclone to the
north enters Guam`s AOR at 25N170E, extending southwest to
northwest of Wake Island at 22N161E, where it transitions to a
TUTT axis that extends southwest to Guam. Divergence along and
south of these trough axes are supporting scattered shower
development along its length and points south of there. A few
thunderstorms are also developing north of Wake Island due to
steeper mid-level lapse rates, and across the Marianas near Invest
95W due to deep tropical moisture and lift.

Over the next few days, a building east-west ridge of high
pressure in the mid latitudes will force a strengthening TUTT (due
to a tightening pressure gradient) to set up from near 20N180 to
a cell that`ll develop south of Wake Island near 16N155E to
another potential weak cell across the Marianas where it may end.
This could allow for greater convective coverage across the
Marianas and the open ocean east of there.

...ITCZ...
The ITCZ remains ill-defined with some semblance of it stretching
from north of Kwajalein east to the Date Line. The models show
this feature remaining poorly defined over the next few days,
possibly into early next week, with any relevant convection tied
to embedded surface troughs.

$$

Doll/Cruz