946
FXPQ50 PGUM 081846
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
446 AM ChST Thu Oct 9 2025

.Marianas Update...
The forecast for today was improved, with scattered showers reduced
to isolated for the Marianas. The core of heavier showers and
thunderstorms east of the Marianas overnight shifted southwestward,
passing just south of Guam. Expect isolated showers and thunderstorms
today with partly sunny skies. An approaching trough will still bring
more showers tonight. Upper-level support will still support briefly
heavy showers and thunderstorms.

&&

.Tropical Systems...
Invest 95W, northwest of the Marianas was upgraded to Tropical
Depression 29W late Wednesday evening, and later upgraded to Tropical
Storm Nakri, early this morning by the Joint Typhoon Warning Center.
Nakri sits well northwest of the Marianas and north of Yap/Palau, and
will continue away from these areas, eventually pushing north of the
WFO Guam Area of Responsibility (25N). There are currently no other
suspect areas for development in the region, but we will see weak
disturbances push through Micronesia in the coming week.

&&

.Eastern Micronesia Update...
Relatively fair weather prevails across most of the main islands in
the region. However, due to the proximity of a surface trough, some
upper-level support and satellite trends, opted to add in isolated
thunderstorms at Majuro for today. Bulk of the showers should keep
just outside the northern Majuro waters today. Expect gentle winds
for much of the period through the weekend as a couple surface
troughs/disturbances push westward through the region. Combined seas
will be around 3 to 5 feet with a long period north swell entering
the region early next week.

&&

.Western Micronesia Update...
A busy pattern is shaping up with a broad trough generating showers
and thunderstorms between Yap Proper and Weno, Chuuk. Fair weather
sits in place for now at Yap and Palau, but showers and thunderstorms
will shift westward through the morning. Spotty showers are beginning
to fire up near, and upstream of, Weno. The present monsoon pattern
near Yap and Palau will continue to weaken as Tropical Storm Nakri,
well to the north, pulls farther away, giving way to lighter and
more variable winds in the coming days.

&&

.Prev discussion... /issued 934 PM ChST Wed Oct 8 2025/

Marianas Synopsis...
Satellite imagery shows partly cloudy skies to the east and mostly
cloudy skies to the west, while radar shows isolated to isolated
showers across the region. Buoy data shows sea heights of about 5
feet.

Discussion...
A weak ridge has followed behind Invest 95W and is producing
pleasant weather to the islands tonight. However, that is not
expected to last as a broad trough will be moving into the region
from the east. This trough is already producing scattered showers and
isolated thunderstorms to the east. Once this trough passes, a return
to a trade-wind pattern is anticipated for the weekend.

Model guidance shows in the longer term, that a east-west trough in
Yap State may produce a tropical disturbance. While models suggest it
will mostly remain in Yap State, this system may cause a convergence
zone over the Marianas and produce some showers around the beginning
of next week. However, at this time impacts are anticipated to be
minimal.

Marine...
Winds will be mainly light to gentle this week, and will build to
gentle to moderate around Sunday. Combined seas of 3 to 5 feet will
continue through Friday, then the seas are expected to build to 5 to
7 feet for the weekend due to the distant Typhoon Halong producing a
north swell.

For the surf, there remains a moderate risk of rip currents along
east facing reefs and a low risk on all other reefs through at least
Friday. Around Saturday, the north swell (from Typhoon Halong) is
anticipated to arrive and build the surf up to around 6 feet and
produce a moderate risk of rip currents along north facing reefs.

Tropical Systems...
A newly formed Tropical Depression Nakri (29W) is centered near
20N138E well northwest of the Marianas. This system is moving
north-northwest at 8 mph, with maximum sustained winds at 30 mph near
the center of the closed Low-Level Circulation (LLC). This system is
expected to continue to move in this general direction toward
Okinawa, Japan, followed by a slight acceleration in forward speed by
Thursday. In addition, the system is expected to slowly intensify on
approach toward the Ryukyu chain, possibly becoming a tropical storm
early Thursday morning. This system is not expected to have any
direct impact to any islands in NWS Guam`s Area of Responsibility
(AOR).

Eastern Micronesia...
Increasing surface convergence is leading to low-end scattered shower
development east of Pohnpei and Kosrae. We thought about going
slightly higher with 40 or 50 percent chances for tonight, but given
how small the showers are, opted to maintain a more conservative
approach. However, if satellite trends show them continuing to
increase in coverage, a late afternoon/early evening update remains
possible. Otherwise, these areas will see shower coverage drop back
to isolated coverage by Thursday night, with isolated showers
continuing for Majuro.

It remains to be seen how active of an ITCZ we may have towards the
weekend and into early next week (will it be just trade convergence
denoting the ITCZ or will appreciable convection develop along it?).
The GFS GDI (Galvez-Davison Index) is less than impressive, as is its
precipitation fields. The ECMWF isn`t much better even when
considering its wet bias. looking upstream convergence increases east
of the Date Line, as does convection once you get near 160W, so maybe
next week will allow the ITCZ to become somewhat more active.

AS for seas, they`ll hold in the 3 to 5 foot range for a few more
days, before increasing over the weekend and for the first half of
next week. This is due to a northerly swell arriving with a somewhat
long period of 12 to 14 seconds (depending which model you look at).
This will definitely add some chop to the waters by then. As for
winds, they`ll remain light to gentle through early next week.

Western Micronesia...
A southwesterly monsoon will continue to bring unsettled weather to
Palau through Friday and, to some extent, Yap tonight. These on-and-
off showers and some thunderstorms will bring moderate to
occasionally strong winds to Palau tonight, before slowing
significantly over the next few days as winds diminish across much of
western Micronesia, as a ridge extending across the Marianas to the
northeast dips down slightly through Thursday. After a brief period
of drier weather at Yap on Thursday, an east-west oriented trough is
expected to form, extending from a potential tropical disturbance
in eastern Yap State to then follow said trough`s axis on its way
west, with little significant impact expected to the region at this
time. Low-end scattered showers are expected for much of the forecast
period at Chuuk, as gentle to moderate trades continue and bring a
period of drier conditions during the weekend, followed by increasing
showers next week.

Combined seas of 3 to 5 feet are expected across the region through
the weekend, before increasing slightly near Chuuk as a northerly
swell emanating from a distant Typhoon Halong near Japan, makes its
way across the area. Pulses of southwest swell are expected to make
their way across Palau and Yap the next few days, before various
northerly swells overtake the monsoon swell during the weekend.
This will cause surf to build along north-facing reefs, while
diminishing along south and west reefs of Palau and Yap. At this
time, no significant marine and/or surf impacts are expected by these
swells.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
MP...None.
Marianas Waters...None.
&&

$$

Marianas: Aydlett