530
FXPQ50 PGUM 291913
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
513 AM ChST Wed Sep 30 2026

.Marianas Update...
Satellite imagery and radar show increasing cloud cover and showers
across the Marianas as Invest 93W approaches the region. Altimetry
shows combined seas are between 3 and 5 feet.

Overall, this forecast package is consistent with the previous
forecast. Shower coverage was bumped up to high-end (50%) scattered
based on the proximity of Invest 93W and outer bands. As Invest 93W
approaches the region, showers and thunderstorms will increase along
with wind. Uncertainty remains high on the closest approach to the
Marianas for 93W. Some guidance halts all westerly motion of the
storm and turns it northward well east of the Marianas. This would
delay some of the impact to the region with the bulk of the impacts
resulting from the trailing monsoonal flow. A different set of
guidance shows 93W continuing westward through or just past the
Marianas before stalling and turning north. This solution leads to
higher impacts from the southern periphery of 93W and the monsoonal
trough to the south. This would set up a prolonged heavy rainfall and
windy conditions across the Marianas.

No changes were made to the marine forecast. Combined seas are
between 3 and 5 feet and will rise quickly over the coming days. Seas
looks to become hazardous to small craft Thursday night or
Friday. Marine conditions will vary greatly depending on the exact
track and strength of Invest 93W. Mariners and boaters should
continue to monitor forecasts for changes over the coming days.

&&

.Tropical Systems Update...
Invest 93W was located at 16N152E and is currently moving west-
northwest. The Joint Typhoon Warning Center has issued a Tropical
Cyclone Formation Alert for Invest 93W. This means that development
into a significant tropical cyclone is expected within 24 hours.
Invest 93W has organized quickly, forming a Central Dense Overcast
overnight. Banding on the south side of the storm has also improved
showing good outflow. Invest 93W is expected to strengthen as it
continues moving west-northwest to northwest over the coming days,
likely passing north of Saipan late in the week. Residents of the
Marianas, especially Tinian, Saipan and the northern CNMI, should
monitor forecasts for any changes to expectations for Invest 93W.

For more information on Invest 93W, see bulletins issued by JTWC
under WMO header ABPW10 PGTW.

&&

.Eastern Micronesia Update...
Satellite imagery shows mostly clear to partly cloudy skies across
Pohnpei and Kosrae and partly to mostly cloudy skies across Majuro.
Altimetry shows combined seas between 4 and 7 feet.

No changes were made with this forecast package. Clear and quiet
weather is expected across eastern Micronesia today. Latest satellite
trends do show showers and thunderstorms south of Majuro, but these
showers and storms are expected to remain south of Majuro.

No changes were made to the marine forecast. Combined seas of 4 to 7
feet will continue through much of the period.

&&

.Western Micronesia Update...
Isolated showers are seen across Palau, and scattered showers are
seen across Yap and Chuuk. Altimetry shows combined seas between 3
and 6 feet.

No changes were made with this package. The weather pattern
continues to be dominated by the monsoonal showers and thunderstorms
across Yap and northern Chuuk State and the surface ridge near and to
the south of Palau. Yap is expected to remain active through the
period with the monsoon-like trough remaining just north of Yap
State. Showers look to increase across Palau this week as a
developing monsoon surge sets up over the region. Chuuk will seeing
clearing weather conditions this week.

No changes were made to marine forecast. There is some potential for
seas approaching hazardous levels at Yap and Palau next week, but
this is depends on the track and intensity of Invest 93W. Choppy
seas are expected for Yap by Friday and Palau by Sunday.

&&

.Prev discussion... /issued 655 PM ChST Tue Sep 29 2026/

Marianas Synopsis...
Light to gentle westerlies prevail across the Marianas. Satellite
imagery and Doppler radar indicate a convergence zone developing
to the east of the island chain. Recent altimetry passes indicate
seas are around 3 to 4 feet.

Discussion...
An unsettled weather pattern produced by an extensive monsoon trough
dominated primarily by a developing disturbance known as Invest 93W
well to the east, will continue for at least a few more days. Mostly
dry conditions are expected overnight, followed by some patchy
showers developing Wednesday as the southwesterly monsoon continues
to build. Conditions will deteriorate as Invest 93W continues to
consolidate and pass to the northeast of the Marianas sometime
Friday through Saturday, inducing a significant monsoon surge that
will bring a peak in shower and thunder potential by the weekend.
Conditions are then expected to remain wet coming into next week as a
southwesterly monsoon regime continues.

Marine...
Combined seas of 3 to 4 feet will increase over the coming days, as
Invest 93W continues to consolidate to the east of the Marianas and
allows a southwesterly monsoon to return across the region toward the
weekend. As 93W passes to the northeast and a monsoon surge develops,
seas are expected to surpass 10 feet beginning Friday, likely
becoming hazardous to small craft. A moderate risk of rip currents
is expected to develop along east facing reefs of the Marianas
beginning Wednesday, to then develop all reefs Wednesday night as a
strengthening southwesterly swell envelops the region. There is some
likelihood for hazardous surf to develop along south, west and north
facing reefs of the Marianas by the weekend, highly dependent on the
development of 93W and associated southwesterly monsoon surge.

Tropical Systems...
A developing disturbance found along the monsoon trough, Invest 93W,
is centered east of Saipan near 15.2N 155.5E. 93W is now rated
medium by the Joint Typhoon Warning Center (JTWC), meaning that
development into a significant tropical cyclone (tropical
depression) is expected, but not within the next 24 hours. Invest
93W continues to move slowly west-northwest. Convection has been
persistent to the west through north of the center. Invest 93W is
expected to slowly strengthen as it continues moving west-northwest
to northwest over the coming days, likely passing north of Saipan
late in the week. Residents of the Marianas, especially Tinian,
Saipan and the northern CNMI, should monitor forecasts for any
changes to expectations for Invest 93W.

For more information on Invest 93W, see bulletins issued by JTWC
under WMO header ABPW10 PGTW.

Eastern Micronesia...
Not much happening across eastern Micronesia this afternoon. Latest
guidance still showing a very dry pattern continuing for the next
several days across Pohnpei and Kosrae, with POPs (Probability of
Precipitation) remaining in the 10 percent range for Pohnpei and 20
percent for Kosrae. For Majuro, inflow and increased convergence due
to strengthening Invest 93W is still expected to bring increased
convection to the Marshalls beginning Wednesday night and continuing
through the weekend. No major changes were made to the marine
forecast.

Western Micronesia...
The monsoon trough remains the dominant feature effecting the
region. The showers associated with this feature are over Palau and
Yap, This feature is producing up to scattered and isolated
thunderstorms, with the most active showers are northwest of Palau.
As Invest 93W consolidates and moves west-northwest, the monsoon
trough is north of the domain is expected to turn into a more NE-SW
direction.

Palau is inbetween decaying showers produced by the convergences of
the monsoon trough and southwesterly winds, showers will vary
between isolated and scattered through about Thursday as this
convergence shifts with 93W`s consolidation. For the weekend,
showers are expected to scattered as the monsoon surge passes over
the island.

Today at Yap, showers of diminished over the island. Showers are
expected to build back in this evening and remain through the rest
of the week as 93W consolidates and bring a monsoon surge over the
island. Model guidance suggests up to 1 inch of rain each day through
the remainder of the week. Overall, a wet week is to be expected.

Chuuk is on the southern edge of the convective activity produced by
the monsoon trough. Here is where blow-off cloud cover is the
greatest. This cloud cover is expected to produce isolated showers
while the trough remains in a E-W orientation. Once 93W starts
pulling the trough away, drier conditions are expected to return
for the weekend and into next week.

Altimetry shows combined seas between 3 and 5 feet across the
region. Winds will be light to moderate through Thursday, then winds
are expected to build to gentle to fresh near the weekend. Sea
conditions are expected to remain benign through Thursday, then seas
are anticipated to build to around 7 to 8 feet for the weekend and
beginning of next week.

&&

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

$$


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