143
FXPQ50 PGUM 100817
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
617 PM ChST Wed Dec 10 2025

.Marianas Synopsis...
Satellite imagery shows partly cloudy skies, while radar imagery
shows isolated showers over coastal waters. Altimetry shows combined
seas of 6 to 8 feet to the east of the islands and 7 to 9 feet to
the far northwest.

&&

.Discussion...
The main weather maker is the incoming shear line that is making its
way from the far northern islands of CNMI into Saipan over the next
24 to 36 hours or so. This shear line is fairly dry, which is
reflected in the forecast with the use of intermittent light
showers for Tinian and Saipan for Thursday night. The main concerns
with this shear line are the winds. These winds are expected to be 15
to 25 mph with gusts up to 30 mph. Once this shear line passes,
pleasant weather is expected to return through the middle of next
week.

&&

.Marine...
Marine conditions are expected to deteriorate over the next several
days as a shear line will move south near Saipan and Tinian.
Combined seas are 6 to 7 feet, and are expected to build a foot or
two and even higher for Tinian and Saipan over the weekend. Seas near
Tinian and Saipan may build to 11 feet over the weekend. A north
swell may make its presence known over the weekend, making seas even
more choppy. Assuming this comes to pass, these sea heights will
require a Small Craft Advisory. Once this shear line passes, seas
are expected to gradually taper down.

&&

.Eastern Micronesia...
The main weather features to watch are the Near-Equatorial Trough
(NET) and a surface trough east of Majuro. A buffer circulation has
developed near 2N165E, southeast of Kosrae. Although no strengthening
of this feature will occur, it`s just close enough to bring lower-
end scattered shower coverage to Kosrae over Thursday, mainly for the
southern coastal waters. Otherwise, isolated showers will continue
through at Least saturday for Pohnpei and Kosrae.

Farther east at Majuro, an approaching surface trough will interact
with an upper trough that`s continuing to provide enough divergence
to foster scattered shower development along the trough, with a few
thunderstorms mixed in. This could bring lower-end scattered shower
coverage to Majuro Thursday and Thursday night. However,
thunderstorms aren`t expected as the trough weakens and heads east,
decreasing instability and lift enough to preclude thunderstorm
development.

As for marine conditions, winds will generally remain in the gentle
to moderate range area-wide, perhaps becoming moderate to strong at
Majuro from time to time. Seas of 5 to 7 feet may build a foot or so
for the start of next week.

&&

.Western Micronesia...
A fairly dry trade-wind pattern continues. Himawari visible satellite
this afternoon shows isolated to scattered showers near Yap Proper
moving westward and away, and just east of Palau waters, associated
with shallow troughing within the trades north of the Near-
Equatorial Trough (NET). The portion of the NET south of Palau has
shifted slightly northward, which looks to support low-end scattered
showers (30 percent chance) over Palau waters tonight as a shallow
trough moves in from the east. Much further east, a weak circulation
is seen, embedded within the NET to the south-southwest of Chuuk.
Scattered to numerous showers and isolated thunderstorms are seen
along the northwest to north flanks of the elongated circulation,
mainly over eastern Yap State south of Satawal. Upper-level cloud
debris from this and other showers along the NET are blanketing much
of the area, but conditions are mostly dry over Chuuk Lagoon and
upstream. Model guidance depicts the embedded circulation dissipating
within the NET over the next day or so.

The NET looks to shift back towards the south for Thursday through
the rest of the week, slightly away from Koror, but a series of
weak, transient trade-wind disturbances will still bring scattered
showers from time to time for Yap and Palau through the coming
weekend. For Chuuk, a stable trade-wind regime will prevail through
the end of the week. Then, a weak disturbance looks to develop to
the south or southeast of coastal waters and build northwest,
increasing showers near and south of Chuuk from around Sunday night
through early next week.

Recent satellite altimetry indicates combined seas of 4 to 6 feet
near Palau and 5 to 7 feet for Yap and Chuuk, comprised of the
primary northeast trade swell and a background north swell, which
is expected to weaken through the end of the week as it becomes
indistinct from the trade swell. Seas look to increase a foot or so
this weekend as stronger east to northeast trade swell moves into
the region, associated with surging trade winds to the north and
northeast. Early next week, a pulse of long-period north swell looks
to move into Chuuk State, emanating from distant strong mid-latitude
systems. Winds will be gentle to moderate throughout the forecast
period, increasing to fresh at times this coming weekend for Yap and
Chuuk.

&&

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

$$

Marianas: Bowsher
East Micronesia: Doll
West Micronesia: DeCou