277
FXPQ50 PGUM 172301
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
901 AM ChST Tue Aug 18 2026

.Eastern Micronesia Update...
As expected, a recent altimetry pass right over Majuro showed seas of
6 feet, a solid 2 feet below advisory thresholds. As such, the High
Surf Advisory has been cancelled.

At Pohnpei, the 20-25 knot winds well southwest of Pohnpei yesterday
were convectively, contaminated. With less robust (not as
strong/intense) shower and thunderstorm development overnight, while
also considering Invest 92W remains weak (which should continue for
another 30 to 48 hours), the pressure gradient will remain weaker,
with no increase in sustained winds likely until 92W starts its
intensification cycle. Again, this looks to be Wednesday, but it
could be delayed longer. Until then, based on scatterometer data and
forecaster experience, the Small Craft Advisory was cancelled.

As for precipitation, the frequent heavy showers have developed, but
they`re southwest of Pohnpei and northeast of Kosrae. Visible imagery
does show this trying to build towards both locations though. As
such, the forecast was updated to reflect satellite trends, with the
heavier activity delayed until this evening. we`ll continue to
monitor this potential.

&&

.Prev discussion... /issued 551 AM ChST Tue Aug 18 2026/

Marianas Update...
Light winds may allow for island-effect convection this afternoon,
especially for western Guam where the hi-res guidance is showing the
best potential. Invest 92W is embedded in a broad surface trough and
this trough will keep showers chances elevated through the rest of
week with isolated thunderstorms also expected. There is still much
uncertainty associated with Invest 92W, residents of the Marianas
should continue to be up-to-date on the forecast over the coming
days. Combined seas of 4 to 6 feet will continue for the next several
days. Otherwise, a moderate risk of rip currents along north- and
west-facing reefs will continue for the next several days.

Tropical Systems Update...
Invest 92W is located around 8N156E this morning. The disturbance
continues to be rated as low by the Joint Typhoon Warning Center
(JTWC), meaning development into a tropical cyclone is unlikely
within the next 24 hours. Latest scatterometer pass shows a broad
and elongated low-level circulation and model guidance suggests that
92W will organize and develop, moving to the northwest around
midweek. Residents of the Marianas should continue to monitor the
forecast over the coming days.

Invest 94W is located around 20N133E this morning. The disturbance
is rated as low by JTWC, meaning development into a tropical cyclone
is unlikely within the next 24 hours. Model guidance suggests that
development is suspect with 94W but we will continue to monitor for
any potential organization and development over the coming days.

For more information on Invest 92W and Invest 94W, please see
bulletins issued by JTWC under WMO header ABPW10 PGTW.

Eastern Micronesia Update...
Wet and unsettled weather will continue today and tonight at both
Kosrae and Pohnpei with numerous to widespread locally heavy showers
and isolated thunderstorms expected as moist, southwest flow
continues across the Pohnpei and Kosrae States. Gusts to 30 knots
will be possible with heavier showers and thunderstorms. Scattered
showers and isolated thunderstorms will be possible at Majuro over
the next several days. Fresh to strong southwest winds are expected
at Pohnpei through Tuesday with winds being slightly weaker at
Kosrae, topping out around moderate in strength. Light to gentle west
winds can be expected at Majuro through Tuesday. Combined seas of 7
to 10 feet are expected at Pohnpei, 6 to 8 feet at Kosrae, and 4 to 6
feet at Majuro. A Small Craft Advisory is in effect for the coastal
waters of Pohnpei through 3pm Thursday. A south to southwest swell
will continue to promote hazardous surf along south-facing reefs,
particularly at Kosrae and Majuro where a High Surf Advisory remains
in effect through late this week.

Western Micronesia Update...
Wet and unsettled weather will persist at Chuuk over the next several
days as Invest 92W slowly lifts to the northwest and moist, southwest
flow envelopes portions of Chuuk State. Widespread, locally heavy
showers and isolated thunderstorms can be expected through at least
midweek. Gusty winds up to 30 knots will be possible with heavier
showers and thunderstorms. High pressure will continue to promote
mostly dry conditions across Palau and Yap through at least tonight,
with shower chances topping out at 30 percent. Gentle to moderate
west to southwest winds will continue at all locations over the next
couple of days, before ramping up at Chuuk later in the week.
Combined seas of 3 to 5 feet at Yap and Palau and 5 to 6 feet at
Chuuk will continue over the next couple of days, with seas being
locally choppy at Chuuk near heavier showers and thunderstorms.

Prev discussion... /issued 714 PM ChST Mon Aug 17 2026/

Marianas Synopsis...
Satellite imagery shows partly cloudy skies and isolated showers
across the region. Latest altimetry indicates combined seas of 4 to 6
ft.

Discussion...
With Invests 94W to the northwest and 92W to the southeast, the
Marianas are entering a col, meaning gentle westerlies will gradually
ease to light and variable overnight. Due to the buckling of
westerly flow against the easterlies on the western edge of the col,
scattered showers and isolated thunderstorms are forecasted for Guam
and Rota after midnight. There will be a brief lull in shower
activity in the morning for all islands as the col is overhead. Once
the col exits the region to the west, convergence on its eastern
edges could bring increased shower and thunderstorm potential to the
CNMI in the afternoon. Guam, on the other hand, may see island-effect
showers and isolated thunderstorms in the afternoon. Then, bands of
showers are possible due to the surface trough extending from Invest
92W, so shower coverage may remain scattered through midweek. There
is still high uncertainty regarding a potential approach from Invest
92W as it has been quasi-stationary and slow to develop. However,
model guidance should converge on a solution as the week continues,
so Probability of Precipitation (POP) was limited to 40 percent early
next week. This situation will continue to be monitored closely.

Marine...
A primary westerly swell of 4 ft and secondary north-northeasterly
swell of 3 ft are producing combined seas of 4 to 6 ft, as well as a
moderate risk of rip currents along north- and west-facing reefs
through the week. A long period, elevated northeasterly swell may be
in store early next week should Invest 92W track towards the
Marianas. There is a moderate risk of lightning through the week.

Tropical Systems...
A largely disorganized tropical disturbance, known as JTWC`s Invest
92W, is currently centered near 9N158E well north of Pohnpei. Most
of the wind field and convection is concentrated in the southern
peripheries of 92W, with recent scatterometer passes and visible
satellite analysis indicating sustained 15-20 kt westerlies carrying
a newly-developing monsoon surge embedded within said wind field
between Chuuk and Pohnpei. This will also allow the system to
further consolidate over the coming days, but not likely to develop
into a significant tropical cyclone over the next 24 hours. As the
system continues to develop, it is expected to begin moving to the
north-northwest around midweek, as a secondary disturbance enhanced
by the aforementioned westerlies builds near Palau and Yap in the
second half of the week. This chain of systems could influence a
large section of the region for an extensive period of time, so do
regularly check the forecasts for more updates as these events
develop over the week. For more information regarding impacts to
Pohnpei and Chuuk, refer to the Special Weather Statement SPSPQ1 for
Pohnpei, and Special Weather Statement SPSPQ2 for Chuuk,
respectively. For more information on Invest 92W, see bulletins
issued by JTWC under WMO header ABPW10 PGTW.

Eastern Micronesia...
The southwesterly monsoon flow continues across the region, with
Pohnpei seeing over 4 inches on the northwest side of the island, and
additional heavy rainfall continuing at times for Kosrae. Some of the
atolls of the RMI have also seen this, with Mili Atoll showing over
an inch in one hour. A Special Weather Statement remains in effect
for Pohnpei and Kosrae, with Pohnpei looking to have the highest
potential for heavy rainfall and frequent gusts to 30 knots
continuing through the middle of the week. This is due to Invest 92W
continuing to remain weak/slow to develop. This is allowing the
tropical disturbance to linger in the vicinity, with the latest
analyzed position from JTWC (Joint Typhoon Warning Center) having
shifted the position south, with the LLCC (Low-Level Circulation
Center) now centered near 9.2N 157.8E.

The models do show this system lifting off to the north-northwest
towards the weekend. Until then, it looks to remain quasi-stationary
over the coming days. As this occurs, the bulk of the model guidance
shows the west to southwest wind fields increasing in strength over
the next 72 hours, particularly near Pohnpei, as 92W attempts to
become better organized. In the mean time, given satellite trends
and model data, we kept categorical POPs (Probability of
Precipitation) going at Pohnpei and Kosrae for the next 36 hours,
using frequent shower wording, as there will likely be some lulls in
between the heavier rainfall, as the atmosphere temporarily
stratifies (stabilizes) in the low levels. For the latter half of
the week, lingering monsoonal flow along with cross equatorial flow
will keep scattered showers in the forecast for Pohnpei and Kosrae.

Hazardous marine and coastal conditions are ongoing across eastern
Micronesia. For Pohnpei, a Small Craft Advisory was issued this
evening, mainly for frequent gusts tonight and Tuesday, and then
sustained winds and seas Tuesday night through Thursday afternoon. A
High Surf Advisory is in effect along south facing reefs until 3 AM
Thursday for Majuro and 3 AM Friday for Kosrae. This swell is
emanating from two sources in the south Pacific. The first is former
Invest 90P, which continues to produce a cross-equatorial flow from
south of the Equator. The second is from a far more distant low
pressure east of New Zealand and distant high pressure south of
Australia. Marine and coastal conditions will see little improvement
until Invest 92W exits the region and the south swell from the south
Pacific weakens.

Western Micronesia...
Satellite observations show partly cloudy skies across Palau and
Yap, and mostly cloudy skies across Chuuk. Altimetry shows combined
seas between 3 and 5 feet across Palau and Yap, and 5 to 7 feet
across Chuuk.

Ridging between the two monsoonal patterns continues to keep dry
conditions across Palau and Yap. This dry pattern looks to persist
through Tuesday for Yap and Wednesday night for Palau. Towards the
latter half of the week, a significant flip in the pattern is
expected. The monsoon trough is expected to bridge across the
region, bringing a monsoon surge. Locally heavy rainfall and gusty
winds will be possible towards the end of the week for Palau and Yap.

Scattered showers are currently present across Chuuk, but shower
coverage is expected to increase to widespread tonight. As Invest
92W lifts northwestward, Chuuk will be positioned within the monsoon
tail this week. Widespread locally heavy showers are expected
through Thursday. Additional rainfall amounts between 4 and 8 inches
will be possible, which may lead to flash flooding and mudslides. At
this time, Invest 92W looks to remain disorganized until it moves
well north of Micronesia. Gusty winds up to 30 knots will remain
possible near heavier showers.

Winds and seas remain 5 to 7 feet across Chuuk and 3 to 5 feet
across Palau and Yap. Combined seas look to remain benign across
Palau and Yap through Thursday and then look to become choppy on
Friday and going into the weekend. Choppy seas will persist across
Chuuk through the week, making inter-island travel difficult. As the
monsoon surge intensifies south of Invest 92W, winds will increase to
25 kt sustained with gusts to 35 kt late this week across Chuuk.
This will lead to conditions hazardous to small craft by Thursday. A
Small Craft Advisory will likely be needed within the next few
forecast packages.

&&

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

$$

Marianas: Mesa
East/West Micronesia: Doll