275
FXPQ50 PGUM 230819
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
619 PM ChST Sat Aug 23 2025

.Marianas Synopsis...
Radar and satellite imagery shows scattered showers and isolated
thunderstorms over the Marianas. Altimetry and buoys show combined
seas of 2 to 3 feet. Winds are gentle to moderate. This morning was
not as wet as the past day or so, but 0.18 inches of rain had fallen
at the Guam International Airport by this afternoon.

&&

.Discussion...
The convergence zone behind a broad trough is producing scattered
showers and isolated thunderstorms for the Marianas and nearby
waters and is expected to continue through tonight and Sunday. This
pattern is expected to continue through the forecast period, due to
more trade-wind troughs and upper-level divergence. Scattered
showers and isolated thunderstorms should be expected for the next
few days. Around Monday night, a brief lull is anticipated for 12-24
hours. Then showers may return for the rest of the forecast period.

&&

.Marine...
Combined seas are anticipated to gradually rise by about a foot by
Tuesday. This will cause the surf along east facing reefs to meet the
threshold of 5 feet. This will cause the risk of rip currents to
become moderate along east facing reefs. There is also a moderate
risk of lightning through at least Tuesday.

&&

.Tropical Systems...
A tropical disturbance, located just south of Palau near 6.5N 134.1E,
has just been designated Invest 93W by the Joint Typhoon Warning
Center. The latest round of convection this afternoon, focused near
the center of 93W, is currently stratifying out near Palau with
visible satellite indicating a thinning cloud deck overhead, with
the heaviest showers currently displaced roughly 100 miles north,
150 miles south and 200 miles west of the circulation center. An
ASCAT pass over the disturbance this morning indicated wind speeds up
to around 30 knots within the heavy showers just east of the center,
with somewhat questionable gale force winds exceeding 34 knots
within the deep convection west of the center. Latest model guidance
indicates Invest 93W will meander northwest through the remainder of
the weekend with little change in strength or organization. 93W
should pass to the southwest of Palau overnight and exit the region
west of 130E around Sunday night or early Monday morning. As 93W
passes nearby, Palau can expect scattered to numerous showers and
isolated thunderstorms overnight with locally heavy showers possible,
with gradually diminishing showers anticipated through early next
week. Strong gusts of 25 to 30 knots will be possible near the
heaviest showers, but the highest winds look to be focused south and
west of Palau waters as 93W passes by.

For more information on Invest 93W, see bulletins by the Joint
Typhoon Warning Center under header ABPW10 PGTW, as available.

&&

.Eastern Micronesia...
A dry trade-wind pattern is in place across eastern Micronesia this
afternoon. A weak Inter-Tropical Convergence Zone (ITCZ) is seen
passing through from east of Majuro to Kwajalein. A trade-wind trough
seen along the Date Line is moving west along the ITCZ and is
expected to bring increased convection to Majuro later tonight.
Model guidance continues to show the ITCZ strengthening and moving
west toward Kosrae and Pohnpei. However, previous guidance also
indicated the ITCZ being active now. Therefore, maintained scattered
showers in the forecast beginning Sunday night, but lowered the POPs
(Probability of Precipitation) from 40 to 50% range to 30 to 40%.

A slight change in the marine forecast. A weak surge in the trade-
wind swell will result in seas increasing to between 5 and 6 feet
Sunday through Monday for Kosrae and Majuro, while Pohnpei will see 5
to 6 foot seas Sunday night. Seas look to drop to 3 to 4 feet at
Pohnpei and Kosrae and between 4 and 5 feet at Majuro by the middle
of next week. Light to gentle winds are expected at Kosrae and
Pohnpei through Thursday, with light to moderate winds at Majuro
through Monday night, dropping to light to gentle.

&&

.Western Micronesia...
The surface circulation near Palau continues to consolidate, and has
just been designated Invest 93W by the Joint Typhoon Warning Center
(JTWC), currently located near 6.5N 134.1E. An ASCAT pass over the
center also placed it just south-southwest of Koror this morning.
Scatterometry wind speeds of 30 knots are seen near the center and
within showers along the eastern flank, with some data points west of
the center indicating gale-force gusts exceeding 34 knots. However,
given very heavy showers in the area at the time (which can
contaminate scatterometry data) and questionable wind directions
associated with the highest values, some of these data points are
questionable. Nevertheless, the possibility for near-gale force
wind gusts is there, especially within heavier showers near the
center.

According to latest visible satellite, cloud cover over Palau looks
to be thinning at the moment as an earlier burst of convection
fizzles out, but additional rounds of showers and isolated
thunderstorms are anticipated through the evening and overnight as
Invest 93W meanders northwest. Model guidance points to the highest
winds and heaviest showers being focused to the south and west of
Palau as 93W passes by, with a general decrease in showers after
midnight, but this will depend on the timing of additional rounds of
convection overnight, as well as the movement/strength of Invest 93W.
Locally heavy showers will be possible, with higher gusts to 25
knots anticipated over Palau and coastal waters, near these heavier
showers. For now, have maintained numerous showers through the
evening (60% probability) with a decrease to scattered coverage (40%)
after midnight for Palau. 93W looks to pass to the southeast of Palau
overnight with little change in strength or organization, eventually
exiting the region west of 130W around Sunday night or early Monday
morning as it moves north-northwest over the Philippine Sea.

To the northeast, Yap remains along the outer periphery of the
heavier shower bands, but can still expect scattered coverage over
the next few days as 93W moves on, and additional weak troughs pass
into the area. A more robust trough/disturbance looks to enter the
area around midweek, leading to a wetter period for Palau and Yap
for Wednesday and Thursday.

To the east, Chuuk remains in a quieter weather pattern this evening
with just isolated to scattered showers nearby, but these will
increase over Chuuk Lagoon overnight as a trough moves into the area.
A more robust, ITCZ-like disturbance will cross the area around
midweek, leading to a wet pattern for the latter half of the week.

Benign marine conditions continue, with altimetry data showing 3 to 4
foot seas throughout the region, mainly comprised of the primary
trade swell. However, models indicate a pulse of south to southwest
swell energy will move into Palau waters overnight, generated by the
developing monsoon pattern in the region. Palau can expect seas to
increase by a foot or so over the next few days as the south to
southwest swell takes over as the primary swell, lingering for much
of the coming week. Yap will continue to see an easterly trade swell
which will gradually shift southeast through the next few days. A
weak surge in the trade swell will increase seas by a foot or so near
Chuuk early next week.

&&

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

$$

Marianas: Bowsher
East Micronesia: Kleeschulte
West Micronesia/Tropical Systems: DeCou