332
FXPQ50 PGUM 121957
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
557 AM ChST Sun Sep 13 2026

.Marianas Update...
Satellite imagery and doppler radar show partly cloudy skies and
isolated showers across the Marianas. Altimetry shows combined seas
between 3 and 4 feet.

No changes were made with this forecast package. The main concern
continues to be island showers and thunderstorms for Guam. Model
Time-Heights show light easterly winds with increasing moisture. This
will generally favor the western portions of Guam once again today.
The ECMWF suggests on Monday there may be better potential for storms
to get trapped over the island in addition to an increase in
moisture. Towards the middle part of next week we will start to see
the influence from Invest 90W. Uncertainty remains on where 90W will
develop, but an increase in showers will be possible well away from
the tropical disturbance.

No changes were made to the marine forecast. Benign seas are expected
to continue through the period.

&&

Tropical Systems Update...

JTWC Invest 90W was upgraded to low overnight. Invest 90W remains
greatly disorganized and broad, centered near 12.5N, 156.6E.
Development into a tropical cyclone is possible but not expected in
the next 24 hours. Model guidance generally favors development beyond
24 hours.

For more information on Invest 90W please see JTWC bulletin APBW10.

&&

.Eastern Micronesia Update...
Satellite imagery shows scattered showers across Pohnpei and numerous
showers across Majuro with isolated thunderstorms across both
locations. Isolated showers are seen across Kosrae. Altimetry shows
combined seas between 6 and 8 feet.

The only change with this package was to start Pohnpei with scattered
showers in the morning becoming numerous in the afternoon. Latest
satellite imagery shows shower coverage is increasing and could
become numerous in a few hours. Otherwise, the next concern is the
continued convection over Majuro. Shower coverage is expected to
decrease to scattered this afternoon, but additional convection
continues to develop along a weak circulation to the east of Majuro.

Choppy seas will continue across the region through the next several
days. Inter-island travel could be difficult at times, especially
near showers and thunderstorms.

&&

.Western Micronesia Update...
Satellite imagery shows scattered showers across Palau, and numerous
showers and isolated thunderstorms across Chuuk. Isolated showers are
observed over Yap. Altimetry shows combined seas between 3 and 5 feet
across Palau and Yap, and 5 to 7 feet across Chuuk.

The only change with this forecast was to increase showers to
numerous across Chuuk this morning. Shower coverage looks to re-
orient itself this afternoon as Invest 90W begins to develop to the
northeast. However, low level convergence could keep heavy showers
over Chuuk through the day. Scattered showers and isolated
thunderstorms will build across Palau today. The pattern looks to
remain active over the coming days for Palau while Yap looks to stay
dry.

Benign seas will continue for Yap and Palau through the period.
Choppy seas will continue for Chuuk over the next day or two. Inter-
island travel could be difficult at times near heavier showers.

&&

.Prev discussion... /issued 601 PM ChST Sat Sep 12 2026/

Marianas Synopsis...
Partly cloudy skies with isolated showers and light to gentle winds
prevail across the Marianas this afternoon. Altimetry shows seas
between 3 and 5 feet.

Discussion...
Fairly dry conditions are expected over the Marianas for the next
couple of days. The exception will be Guam during the afternoon
Sunday and Monday, with the light winds and low cloud cover allowing
island convection both days, giving the island scattered showers and
a possible thunderstorms or two. By Tuesday, increasing convection
will spread over the islands as a weak disturbance approaches closer
to the Marianas as it heads toward the there are three main feature
affecting the region, first northern CNMI. By the end of next week,
a dry pattern returns to the region and continues into the weekend.

Marine/Surf...
Not much going on in the marine or surf forecast. Light to gentle
winds will continue through the middle of next week, with seas of 3
to 5 feet building a bit toward the end of the week, reaching 5 to 7
feet. For now, most of the waters will see 3 to 4 foot swell. The
exception is the far eastern waters where altimetry is showing seas
of around 5 feet. Near the coast, however, swell should remain around
3 feet, producing a surf of 3 to 5 feet along east facing reefs,
resulting in a moderate risk of rip currents. All other reefs will
have a low risk of rip currents.

Tropical Systems...
A weak disturbance found along the monsoon trough, Invest 90W, is
centered east of the Marianas near 12N156E. Invest 90W is currently
sub-low, meaning development is not expected for the next day or so.
Analyses show mainly a weak, elongated circulation along the monsoon
trough. Invest 90W looks to slowly move north-northwest over the next
few days, with little to no development for the next couple of days,
then slow strengthening as it continues NNW.

Eastern Micronesia...
A trough is moving into Majuro tonight and a there are three main
feature affecting the region, first a band of numerous showers and
isolated thunderstorms is expected to develop over the island.
Locally heavy showers are possible. Winds are light to gentle from
the northwest so any storms that develop will be slow moving. This
band of storms is expected to weaken sometime tomorrow morning, so
shower coverage should return to scattered by the afternoon and
continue through Monday. A brief dry period may occur before a new
wave of moisture enters the region Tuesday. Seas of 6 feet tonight
will decrease a foot or so tomorrow and remain steady.

Scattered showers and isolated thunderstorms will become isolated by
tomorrow for Kosrae, with a dry spell continuing for much of the
forecast period. Scattered showers and isolated thunderstorms may
return by Thursday. Seas will remain at 5 to 6 feet most of the
forecast period.

Pohnpei`s proximity to Invest 90W to the north-northwest will bring
numerous locally heavy showers and isolated thunderstorms to the
island tonight and tomorrow, with gusty winds possible. Seas will
also be elevated through at least tomorrow at 6 to 7 feet. As 90W
pushes to the north-northwest, dryer weather can be expected with
mostly isolated showers. Showers may be scattered Monday night and
Thursday with isolated thunderstorms possible.

Western Micronesia...
The Small Craft Advisory for Chuuk was allowed to expire.

There are two circulations embedded within the monsoon flow, the
first, is located near 10N142E, to the east of Yap Proper, and
Invest 90W mentioned above in the Tropical Systems Section.

The first circulation is producing scattered showers along the
southwestern flank over Palau. This feature is expected to keep
scattered showers over Palau through the middle of next week. This
will provide some much needed rain to the region.

The Invest 90W is pulling a lot of moisture from south of the
Equator. This is producing showers along a convergence axis from
EQ142E to 12N156E, passing over Chuuk lagoon. Satellite imagery shows
scattered showers along this axis, however, model guidance is
showering widespread showers.

Altimetry shows combined seas of 3 to 5 feet for much of Yap State.
The primary swell for Palau and Yap is from the west, while the
primary swell at Chuuk is from the south generated by a low-pressure
system south of the equator. Surf along south and west facing reefs
are expected to be elevated but below the 9 foot threshold for High
Surf Advisory. Winds near Palau are expected to be gentle to fresh,
at Yap winds are expected to be light to moderate, and at Chuuk they
are gentle to fresh.

&&

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

$$


Marianas/East and West Micronesia/Tropical Update: Williams
Marianas: Kleeschulte
East Micronesia: Ogle
West Micronesia: Bowsher