978
FXPQ50 PGUM 131958
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
558 AM ChST Mon Sep 14 2026

.Marianas Update...
Satellite imagery shows upper level cirrus moving into the Marianas
this morning. Isolated showers are seen across the region with
numerous showers and isolated thunderstorms just east of the
Marianas. Altimetry shows combined seas are between 3 and 6 feet.

Overall, the only change with this forecast package was to remove
"light" wording for showers across the CNMI. The biggest questions
with the forecast today are whether the upper level clouds from
thunderstorms east of the Marianas limit island showers for Guam
today, and will this convection to our east move into the region.
Uncertainty has increased greatly for island convection on Guam.
Upper level cirrus from showers and thunderstorms just east of the
region have moved over Guam and the Marianas. Island thunderstorms
rely on the heating of the surface to creating rising motion for
thunderstorms. When clouds settle across the region, this limits the
amount the surface can heat up. Shower coverage will likely remain
isolated if island showers fail to develop. At this time, bulk of the
convection to our east is not expected to reach us, however this
convection is associated with a tropical disturbance and slight
changes in development can lead to significant changes in the
forecast.

Combined seas are currently between 3 and 6 feet across the region.
Seas look to remain within this range over the next few days.

&&

.Eastern Micronesia Update...
Satellite imagery shows isolated showers across Pohnpei and Kosrae
and scattered showers across the Marshall Islands. Altimetry shows
combined seas between 5 and 7 feet.

No changes were made with this forecast package. A weak circulation
continues to bring scattered showers to Majuro today. This will keep
scattered showers in the region over the next few days. For Pohnpei,
showers and thunderstorms could develop on the western edge of a
surface ridge. This will allow for scattered showers to return
tonight and on Tuesday. Isolated showers are expected across Kosrae
over the next few days.

Combined seas of 5 to 7 feet will slowly decrease 1 to 2 feet over
the coming days across eastern Micronesia. Some choppy seas will
remain possible near showers and thunderstorms across Majuro and
Pohnpei.

&&

.Western Micronesia Update...
Satellite imagery shows scattered showers across Palau, and isolated
showers across Yap and Chuuk. Altimetry shows combined seas between 4
and 7 feet across Palau and Yap, and 6 to 8 feet across Chuuk.

The main changes with this forecast was to decrease showers across
Yap and Chuuk. For Yap, they remain well within the dry monsoonal
pattern. Guidance does lift the showers and thunderstorms to their
south northward later today, however, guidance has been too quick to
lift the overall pattern northward. For Chuuk, the best forcing has
shifted north of the region. Scattered showers were left in the
forecast due to the broader convergence that could allow for re-
development if showers and storms to the north decay. The forecast
remains consistent for Palau with high-end (50%) scattered showers
expected over the next few days.

Combined seas are between 6 and 8 feet across Chuuk and 4 and 7 feet
across Yap and Palau. A Small Craft Advisory remains in effect across
Chuuk for winds up to 25 kt and occasional gusts to 35 kt. There is
also a High Surf Advisory for south facing reefs of Chuuk. Choppy
seas will be possible across Palau, especially near heavier showers
and thunderstorms.

&&

.Prev discussion... /issued 542 PM ChST Sun Sep 13 2026/

Marianas Synopsis...
Partly cloudy skies with spotty showers are seen across the CNMI,
with mostly cloudy skies and scattered island effect showers seen
over Guam. Light and variable winds prevail across the region.
Altimetry shows seas between 3 and 5 feet.

Discussion...
Island effect showers thunderstorms are the main forecast concern
for Guam over the next couple of days, with light and variable winds
expected for at least the first half of the week. Otherwise,
isolated light showers will be the rule through Monday as the
overall dry pattern continues. For the CNMI, expect increasing
convection Monday night as a weak disturbance passes by to the east
of the islands, coming close enough to the CNMI to bring low-end
scattered showers and possible thunderstorms. This convection will
spread into Guam Tuesday night. This round of showers will be
relatively short- lived, with a dry pattern returning to the region
Wednesday morning. The dry pattern will then continue through next
weekend.

Marine/Surf...
Not much of a change in the marine and surf forecast. Combined seas
of 3 to 5 feet will begin to slowly build around midweek as the
trade-wind swell builds over the area. Surf will slowly increase as
well, reaching up to 5 feet along north facing reefs Monday night,
resulting in a moderate risk of rip currents. The rip current risk
will remain moderate along east facing reefs for the next several
days.

Tropical Systems...
A weak disturbance found along the monsoon trough, Invest 90W, is
centered along an area of sharp troughing, just west of a
circulation center found north of Pohnpei, near 12N156E. 90W is
rated low, meaning development is unlikely over the next 24 hours.
Invest 90W will generally drift NW over the next couple of days and
looks to consolidate within the weak circulation center a little
farther east than the current centroid location. 90W is expected to
slowly strengthen over the coming days as it moves in the general
direction of Maug in the northern CNMI.

For more information on Invest 90W, see bulletins issued by the Joint
Typhoon Warning Center under WMO header ABPW10 PGTW.

Eastern Micronesia...
A trough has moved out of Majuro but environmental conditions
remain unstable so scattered showers and isolated thunderstorms
remain possible tonight and continuing through the entire forecast
period as new troughs move into the area. Gentle winds tonight
will become lighter throughout the week, becoming light and
variable by Wednesday. Seas of 4 to 5 feet are expected to persist
through the whole forecast period.

A ridge has formed over Kosrae and is expected to keep the island
dry through Wednesday with only isolated showers expected. By
Thursday, the monsoon trough may push back into the region and
bring scattered showers and isolated thunderstorms. Seas will
remain at 5 feet for most of the forecast period.

As 90W pushes to the north-northwest, only low end scattered
showers and isolated thunderstorms remain tonight for Pohnpei,
becoming isolated showers by tomorrow. However, the monsoon is
expected to redevelop over the island with more scattered showers
and isolated thunderstorms anticipated Monday night and Tuesday
before another brief dry spell. A new weak trough may develop near
Pohnpei Thursday to bring more precipitation but confidence
remains low. Seas of 5 to 6 feet tonight will continue for at
least the next few days.

Western Micronesia...
A Small Craft and High Surf Advisory has been issued for Chuuk
through at least Tuesday.

The main feature affecting the region is the monsoon flow with a few
embedded circulations, one of which is Invest 90W.

There are two circulations embedded within the monsoon flow, the
first, is located near 12N134E, to the northwest of Yap Proper and
north of Palau, and the second is Invest 90W mentioned above in the
Tropical Systems Section.

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

Invest 90W is located near 12N156E (north of Pohnpei) and is pulling
a lot of moisture from south of the Equator. This is producing
numerous showers along a convergence axis from EQ142E to 12N156E,
passing over Chuuk lagoon. Satellite imagery shows numerous showers
along this axis, however, model guidance is showing widespread
showers. Showers are expected to begin tapering down as early as
Tuesday night. Dry and near breezy conditions are anticipated to
return once this feature moves westward.

Altimetry shows combined seas of 3 to 5 feet for much of Yap State.
Combined seas near Chuuk is estimated to be near 8 feet. 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 facing reefs has exceeded the 9 foot
threshold and a High Surf Advisory has been issued through at least
Tuesday. As features move westward, west facing reefs may also exceed
the 9 foot threshold. Winds near Palau are expected to be gentle to
fresh, winds near Yap are expected to be light to gentle then
building to gentle to fresh for the latter half of the week, and
winds near Chuuk are expected to be moderate to strong with
occasional gusts near-gale. These winds at Chuuk will be closely
monitored. Overall seas near Palau are becoming rougher, seas near
Yap are benign, and seas near Chuuk are under a Small Craft Advisory
due to winds exceeding the 22 knot threshold.

&&

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

$$


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