439
FXPQ50 PGUM 102040
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
640 AM ChST Fri Jul 11 2025

.Marianas Update...
Satellite and radar imagery show developing showers along a trough
near the eastern waters of the Marianas. Thin, upper-level clouds
continue to spread across the region from deeper convection over the
northern CNMI. Ritidian and Ipan buoys continue to show seas between
2 to 3 feet.

Recent developments within the monsoon trough to our northwest,
most notably around Invest 93W near Iwo To, continues to induce a
moist, southeasterly flow over the region. Spotty showers over the
region this morning is expected to increase this afternoon and
tonight due to the nearby trough and convergent southeasterlies in
its wake. There looks to be a peak in shower activity Saturday and
Saturday night and could have a possibility of heavier showers at
times.

Combined seas are expected to build to 4 to 6 feet by Monday due to
an increase in trade swell and southwest swell. A low risk of rip
currents continues along all reefs today, becoming moderate along
east facing reefs tonight due to an increase in trade swell. Surf
along west and south facing reefs also increases slightly as a minor
southwest swell reaches the Marianas tonight.

&&

.Tropical Systems...
The Joint Typhoon Warning Center is monitoring a monsoon disturbance,
Invest 93W, near Iwo To at 24N141E. 93W development potential has
increased somewhat quickly since the Invest was opened yesterday
morning. 93W is now the subject of a Tropical Cyclone Formation
Alert (TCFA), where significant tropical cyclone development is
likely within 24 hours. Deterministic and ensemble models are in good
agreement on a northward track, likely exiting the region (north of
25N) over the next day or so. However, the monsoon tail will still
impact much of the Marianas and western Micronesia.

&&

.Eastern Micronesia Update...
A moderately active Intertropical Convergence Zone (ITCZ) is expected
to be the primary driver of weather in eastern Micronesia for the
rest of the week. Significant showers and thunderstorms will continue
to move across Pohnpei and Kosrae tonight, with conditions expected
to improve considerably at both islands overnight, before picking up
once again at Pohnpei as the trade-wind flow buckles against a
trade-wind disturbance downstream. Showers and thunderstorms may
diminish slightly after, before another pulse in activity within the
ITCZ brings on-and-off showers for at least the first half of next
week.

At Majuro, patchy showers are expected for much of the forecast
period, followed by the aforementioned pulse in the ITCZ that is
expected to bring numerous heavy showers and some thunderstorms by
early next week.

Due to a large trade swell emanating across much of eastern
Micronesia, hazardous surf is expected to continue along Kosrae`s
eastern reefs, so a High Surf Advisory is out through at least early
Sunday morning. Otherwise, the marine forecast remains largely
unchanged for the area.

&&

.Western Micronesia Update...
A busy but unsettled weather pattern induced by a dual-axis monsoon
trough spanning much of the western Pacific, is expected to continue
to produce periods of heavier showers and thunderstorms at Palau and
Yap throughout the forecast period. As a monsoon gyre attempts to
consolidate well northwest of the islands next week, a more
organized southwesterly monsoon pattern may return and bring patchy
showers and some thunderstorms, but uncertainty remains high
regarding the timing of these events.

At Chuuk, shower and thunderstorm coverage is expected to increase
over the coming days as the aforementioned ITCZ buckles against the
general monsoon flow downstream, with numerous showers and isolated
thunderstorms expected during the weekend. Showers are then expected
to diminish quickly thereafter, as a ridge builds in the area by
early next week.

The marine forecast remains unchanged at all three locations.

&&

.Prev discussion... /issued 413 PM ChST Thu Jul 10 2025/

.Marianas Synopsis...
Satellite observations show mainly scattered mid and high clouds with
a few smaller convective lower clouds in vicinity of the islands.
Larger areas of thunderstorms remain outside of the coastal waters to
both the west and the east. Light southeasterly trade winds remain in
place with the surface high far away to the northeast of the area.

&&

.Discussion...
The Marianas are experiencing a relatively quiet weather pattern
between converging monsoon flows and trade winds. Expect a mix of
isolated to scattered showers and isolated thunderstorms over the
next couple days, with a potential for heavier showers over the
weekend and into next week.

&&

.Marine...
Sea state and surf will remain steady, but with a slight increase in
trade swell and sea height, especially for east facing reefs over
the weekend. Both the GFS and ECMWF show an increase in combined seas
this weekend emanating from an easterly swell. Seas only look to rise
1 to 2 feet, but the increase in swell is expected to lead to a
moderate risk for rip currents along east facing reefs this weekend.

.Eastern Micronesia...
Eastern Micronesia will remain under the influence of the Inter-
Tropical Convergence Zone and trade-wind troughs, leading to a
occasionally wet end of the week. Models indicate a broad sustained
increase in trades across eastern Micronesia tonight through the next
few days, bringing moderate to fresh winds throughout the region.
This will lead to increases in trade swell and sea height, and
subsequently an increase in surf, mainly for east-facing reefs. For
Kosrae, surf is expected to remain at hazardous levels of 8 ft until
around Sunday, and the High Surf Advisory has been continued.

Earlier buoy data off Kosrae`s southern shoreline showed combined
seas of around 4 to 6 feet, which are expected to increase another
foot or so through Friday. Earlier altimetry passes showed combined
seas of 5 to 7 feet between Kosrae and Majuro, and 6 to 8 feet east
of Majuro. Seas will continue to rise tonight through the next day or
two, but then trade winds and associated wind waves and swell are
expected to relax early next week.

&&

.Western Micronesia...
Continued unsettled weather due to a convectively active southern
flank of the monsoon trough into early next week. Expect significant
pulses of showers and thunderstorms over the next several days, with
peak potential over the weekend, especially for Palau. Consistent
higher rainfall rates next week could lead to a threat of mudslides,
and this potential will need to be reassessed over the coming
weekend.

&&

.Aviation...
VFR conditions. Isolated heavy showers can quickly drop conditions to
MVFR or IFR CIGS and/or VIS, which would be confined to less than an
hour temporarily.

&&

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

$$

Marianas Update: Cruz
East/West Micronesia Update: Montvila
Tropical: Cruz
Marianas/Micronesia/Aviation: Brenchley