186
FXPQ50 PGUM 220144
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
1144 AM ChST Fri Aug 22 2025

.Update...
Showers have increased over the Marianas. These showers are produced
by the combination of a trade-wind trough and upper-level
divergence. To reflect this, the chance of showers was increased to
70 percent today and to 60 percent tonight.

&&

.Prev discussion... /issued 525 AM ChST Fri Aug 22 2025/

Marianas Update...
Guam Doppler Weather Radar shows scattered showers and isolated
thunderstorms moving through the Marianas Waters. The buoys reveal
combined seas of 3 to 5 feet. The trade-wind trough is currently
oriented southwest to northeast, but the top half looks like it could
be flattening to a more west to east orientation. Rather than the
showers going isolated tonight then scattered again Saturday, this
could just make it scattered all the way through Saturday.

Marine...
Combined seas of 3 to 4 feet surround the Marianas, and most of
Micronesia. Seas could pick up a foot around Tuesday, but should
remain in the 3 to 5 foot range. That could be just enough to bump
the swells to between 3 and 5 feet. This could raise the risk of rip
currents back to moderate along east facing reefs.

Eastern Micronesia Update...
There were only minor changes to Eastern Micronesia this morning.
Raised the PoP`s at Majuro to 40 versus 30. Raised the cloud cover
amounts at Kosrae and Pohnpei. The somewhat active weather here is
being triggered by 2 trade-wind troughs. The first is still east of
Majuro, and so is all of its convection, and will be discussed in
more detail once it`s fully in our area. The second is between
Pohnpei and Kosrae, and is still making weather at both islands.
That`s the main reason why we needed more clouds.

Eastern Micronesia will have winds mainly 5 to 10 knots. There could
be a few 15 knot winds Saturday night and Sunday at Majuro. Seas will
be 3 to 5 feet in the Pohnpei Waters, 3 to 5 feet through Saturday
then 4 to 6 feet at Kosrae Waters, and 4 to 6 feet at Majuro Waters.
While not quite as low as Western Micronesia, these values are still
considered benign marine conditions.

Western Micronesia Update...
There was little or no change to Western Micronesia this morning. A
trade-wind trough lies southeast of Koror Palau and Yap this morning.
A band of high-end scattered showers to the northwest of the trough
axis currently includes both Koror Palau and Yap. An area of winds to
the east of the trough is converging with the trough. This is
creating scattered showers and a few thunderstorms near and southwest
of Chuuk Lagoon. This area of convection will continue to slide
westward, rendering weather at Chuuk mostly sunny after early this
morning. Meanwhile, Palau and Yap have the potential to be wet
through the first half of next week.

All of Western Micronesia will be treated to 5 to 10 knot winds and 2
to 4 foot seas. This will lead to a continuation of benign marine
conditions for the foreseeable future.

Prev discussion... /issued 555 PM ChST Thu Aug 21 2025/

Marianas Synopsis...
Satellite shows scattered showers across the region, with denser
cloud cover over Guam and Rota this afternoon. Radar imagery shows
the deeper convection earlier this afternoon trending down in
intensity and coverage. However, locally heavy showers are still
over southern Guam waters and farther east of the region. Buoys show
steady seas between 3 and 4 feet.

Discussion...
A broad trough extends from an active pattern in western Micronesia.
Overall convergence across the region has increased, with scattered
showers expected through least Friday afternoon. Locally heavy
showers are still possible for Guam and Rota through tonight. Then a
subtle trough may move through Saturday, bringing another period of
scattered showers. Models are showing a bit more organized convection
early next week. This is largely dependent on another tropical
disturbance developing well to the south, so some uncertainty exists,
but more can be gleaned from subsequent model runs.

Marine/Surf...
Locally heavy showers with gusts to 20 kt are possible for Guam and
Rota tonight. Otherwise, combined seas of 3 to 4 feet and light to
gentle winds are expected over the next few days, increasing to 3 to
5 foot seas and gentle to moderate trades next week. There will be a
moderate risk of rip currents along east facing reefs through
tonight. On Friday, the rip risk for east facing reefs drops to low
and rip risk is expected to remain low for all reefs through the
weekend.

Eastern Micronesia...
The main item of interest is a surface trough that stretches from
just northeast of Kosrae to between Kwajalein and Majuro. Another
trough in the trades is located from east of Majuro at 176E between
6N and 12N. Extensive cloud cover with scattered showers will
continue to accompany these features as they head west the next
several days, with a few thunderstorms mixed in from time to time as
well.

As for sea conditions, mainly light to gentle winds may increase
briefly to moderate at times, with seas of 3 to 6 feet expected.

Western Micronesia...
A broad trade-wind trough extends southwest into Yap State from just
east of the Marianas, passing over Ifalik and Eauripik before curving
to the south of Ngulu. Along the forward edge of this trough,
satellite reveals a band of scattered to numerous showers and
isolated thunderstorms extending south-southwest from the Marianas
and across western Yap State, building westward over the Republic of
Palau this afternoon. Scatterometry reveals a few higher gusts of 20
to 25 knots associated with this convection, with otherwise mostly
gentle to moderate trades throughout the region. To the east on the
backside of the trough, satellite shows scattered showers building
over Chuuk, associated with broad trade-wind convergence.

The trade-wind trough will continue to push west and maintain
numerous showers for Palau and Yap overnight. Model consensus
continues to show the development of a weak circulation in the area
along the southern edge of this trough, late overnight through
Friday, then gradually pushing northwest across Palau through
Saturday. ECMWF is being particularly aggressive in depicting this
feature along with the extension of a monsoon trough into the region.
These features will maintain at least scattered shower coverage near
Palau and Yap through early next week. Winds will become light and
variable at times through Monday, looking to gradually shift westerly
across Palau early next week. Chuuk can expect a relatively quieter
forecast period, with a series of weaker troughs crossing the area
late Friday through the weekend, bringing periods of scattered
showers and isolated thunderstorms.

Altimetry data shows benign seas across the region, with combined
seas of around 2 to 3 feet near Palau, 2 to 4 feet near Yap, and
around 3 to 4 feet near Chuuk. Seas look to increase by a foot or two
early next week mainly across Palau waters, as a south to southwest
swell sets up in response to a developing monsoon-like pattern.
However, marine hazards are not expected at this time.

&&

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

$$

Update: Bowsher
Marianas/East and West Micronesia Updates: Stanko
Marianas: Cruz
East Micronesia: Doll
West Micronesia: DeCou