548
FXPQ50 PGUM 162037
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
637 AM ChST Mon Nov 17 2025

.Marianas Update...
Satellite shows that the Marianas remain partly cloudy with isolated
showers. The buoys reveal combined seas of 5 to 7 feet. Winds will
start to increase Friday. The forecast had all this handled, so no
changes were made this morning.

&&

.Marine Update...
The GEFS55 is sticking to its guns on the prediction it made earlier,
still going with a 70 percent chance of a Small Craft advisory for
the Marianas Waters. The most likely time period looks like Thursday
through Saturday.

&&

.Eastern Micronesia Update...
The general forecast philosophy was good, had to make some tweaks due
to the forecast as the shape of the cloud features evolved. Raised
the PoP`s in Pohnpei from 20 to 30, and in Kosrae from 20 to 40,
going from isolated to scattered in each case. Majuro looked fine for
rainfall, just upped the clouds a little, calling them partly sunny.

&&

.Western Micronesia Update...
The Western Micronesia forecast looked good, as it had Chuuk in the
band, and it is. It also had Yap and Koror not in the band of showers,
and they aren`t, at least not today. We`re going to need to keep an
eye on that band, just in case it undulates on top of Yap and Koror,
and we need to issue an update.

&&

.Prev discussion... /issued 528 PM ChST Sun Nov 16 2025/

Marianas Synopsis...
Satellite this afternoon shows isolated showers and partly cloudy
skies across the Marianas, with little variation upstream. Scattered
showers are seen just north of coastal waters, along the forward
edge of a subtle surface trough. Buoy and altimetry data indicate
combined seas around 5 to 7 feet.

Discussion...
A fairly dry trade-wind pattern will prevail through at least
midweek, with increasing shower and thunderstorm chances in the
latter half of the week. A broad surface trough along the leading
edge of a building trade-wind surge will bring scattered showers
around Thursday night into the start of the weekend, likely enhanced
by increased trade-wind speed convergence. Winds will be moderate to
fresh throughout the week, becoming fresher and gustier around
Wednesday night through Friday night.

Marine/Surf...
Moderate to fresh trade winds are expected throughout the week.
Combined seas of 5 to 7 feet will remain steady through Monday night,
then begin to increase as the trade swell builds, potentially
reaching 7 to 9 feet by Thursday night. Seas and winds could increase
further on Friday into the weekend as a trade-wind surge builds
across the region, potentially becoming hazardous to small craft. As
the trade swell increases, surf will increase along east-facing reefs
and likely increase the risk of rip currents to high along those
reefs in the latter half of the week. In the meantime, a moderate
risk of rip currents is expected along north and east facing reefs
for much of the week.

Eastern Micronesia...
Convection has decreased significantly across eastern Micronesia
this afternoon as the Inter-Tropical Convergence Zone (ITCZ) has
fragmented and mostly dissipated across the region. The only active
portion is seen to the north through east of Majuro. This has
allowed the shower coverage to become isolated at all three forecast
points. For Majuro, showers are expected to briefly become scattered
tonight as the weakening ITCZ brushes the atoll and coastal waters.
Then a short dry period is expected to continue through Monday at
Majuro and Kosrae and through Tuesday at Pohnpei. Convection will
again increase at Majuro and Kosrae as the ITCZ reorganizes across
the region. It is expected to lag behind a bit from Pohnpei, though
it should reach the island Tuesday afternoon. Late in the week, the
ITCZ is expected to again fragment into a series of troughs,
allowing drier conditions to move into Majuro Friday, then into
Pohnpei and Kosrae over the weekend.

Latest altimetry data shows seas between 4 and 6 feet for Pohnpei
and Kosrae. The Pohnpei buoy shows seas between 5 and 6 feet, while
the Utwe, Kosrae buoy shows just under 4 feet south of the island.
Seas are between 5 and 7 feet at Majuro with up to 8 feet well east
of the atoll. The seas are due to a combined northeast trade swell,
a small long-period north swell and wind waves. Seas are expected
slowly build over the next couple of days, peaking at around 7 feet
at Pohnpei and Kosrae, and around 8 feet at Majuro near the end of
the week. Gentle to moderate winds are expected at Majuro and
Pohnpei through the week, with mostly gentle winds at Kosrae.

Western Micronesia...
Satellite and surface analysis shows the Near Equatorial Trough (NET)
continues to extend across the region mainly between 3N and 5N from
near 150E to beyond 130E and towards the Philippines. ASCAT derived
winds shows a weak, elongated circulation embedded in the NET in
eastern Yap State, near 4N147E, with passing trade-wind troughs north
of the NET`s axis, moving across Chuuk State and into eastern Yap
State. These features are supporting scattered showers and isolated
thunderstorms across most of Chuuk Sate and into eastern Yap State,
while dry weather extends across Palau and Yap, Proper, were the
Blended Total Precipitable Precipitable Water (TPW) satellite
product shows a layer of drier air with TPW values around 1.8 to 2.2
inches, compared to the 2.3 to 2.7 inches across Chuuk State and
eastern Yap State. The passing trade-wind troughs and embedded
circulation will shift westward towards Yap and Palau Monday night,
bringing scattered showers and isolated thunderstorms to both
locations, along with the potential for occasional gusts to 25 kt
near convection, while Chuuk will see a drying trend as showers
become more isolated in coverage. Weather should dry out fairly
quickly at Yap, but wetter weather is expected to linger at Palau
towards the end of the week as Palau will be located closer to the
axis of the NET. Showers will also start to increase again at Chuuk
Wednesday or Thursday as the next series of troughs move into the
region from eastern Micronesia as the ITCZ redevelops and then
fragments again later in the week.

Altimetry data shows combined seas of 4 to 6 feet across the region,
ASCAT showing winds around 10 to 15 kt across the region, with small
pockets of 20 to 25 kt winds likely associated with ongoing
convection. 10 to 15 kt trade winds with occasional gusts of 25 kt
are expected to continue through the week, but a trade-wind surge is
expected to develop east of the Marianas and mainly north 8N later
this week. This surge will lead to an increase of the primary trade
swell for the latter half of the week. While surf is expected remain
below hazardous levels of 12 feet along east facing reefs, likely
peaking at around 8 to 10 feet, swell wrap around will push surf
along north facing reefs up towards 6 to 8 feet, nearing hazardous
levels of 9 feet. Seas will also build in response to the building
swell, building to 6 to 8 feet, especially across Chuuk State and
eastern Yap State.


&&

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

$$


Marianas/East and West Micronesia Update: Stanko
Marianas: DeCou
East Micronesia: Kleeschulte
West Micronesia: Schank