508
FXPQ50 PGUM 041844
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
444 AM ChST Sat Jul 5 2025

.Marianas Update...
Satellite and radar observations show partly cloudy skies and
isolated showers across the Marianas. Ritidian and Ipan buoys show
combined seas between 2 and 4 feet.

The main change with this forecast package was to decrease shower
coverage over the coastal waters as guidance continues to delay the
scattered showers for the region. Scattered showers do look to be
possible across the region Sunday through Monday as convergence from
southwesterly winds and southeasterly winds intersect the Marianas.
The second change was to add island effect scattered showers and
isolated thunderstorms for Guam and the CNMI today. Light winds aloft
and PWATs approaching 2.25" should allow for some island effect to
take place. Low-level and mid-level wind direction would generally
favor the west coast of Guam today, especially from Apra Harbor to
Tumon bay. The potential for island effect appears greater on
Sunday with guidance showing a south-southwest wind at the surface
and a north-northeast wind aloft. These winds parallel the island but
would be opposite of each other. This means that shortly after
storms go up, they would become nearly stationary. This could lead to
flash flooding where the heaviest rain falls. If guidance continues
to show these weak south-southwest surface winds and weak north-
northeast winds aloft, PoPs may need to be increased for Sunday,
particularly across Guam.

No change was made to the Marine forecast. Combined seas of 2 to 4
feet are expected to continue through the weekend.

&&

.Eastern Micronesia Update...
Satellite shows fairly dry conditions at all three forecast points
across eastern Micronesia this morning. This looks to change through
the day today. A weak Inter-Tropical Convergence Zone (ITCZ) is seen
stretching across the Date Line near 7N, extending west to just south
of Majuro. Along with the ITCZ, there are a few weak trade-wind
troughs traversing the region. These features are expected to bring
increased convection to all three points during the afternoon, with
an unsettled pattern expected to remain across the area through
tonight. No changes were made for the remainder of the forecast.

Benign marine conditions will continue through the middle of next
week, with seas of 4 to 6 feet for Majuro and 3 to 5 feet for Pohnpei
and Kosrae. Light to gentle winds are expected to continue at Pohnpei
through Wednesday next week, with light to gentle winds becoming
occasionally moderate early to midweek next week for Kosrae and
Majuro.

&&

.Western Micronesia Update...
The broad convergent pattern across western Micronesia has weakened
considerably this morning, with convection waning across palau and
Yap. Palau will continue to see low-end scattered showers today with
isolated showers expected by this evening. For Yap, isolated showers
look to continue there through tonight.

For Chuuk, A trade-wind trough has moved west of Weno, with much
drier conditions moving in behind the trough. Farther east, another
weak trough is evident leaving Pohnpei and is expected to bring
increased convection to Chuuk by this evening.

Benign marine conditions will remain across the region, with mostly
light to occasional gentle winds at Palau, Yap and Chuuk. Combined
seas of 2 to 3 feet are expected for Yap Proper and Palau, with seas
of 3 to 4 feet for Chuuk.

&&

.Prev discussion... /issued 439 PM ChST Fri Jul 4 2025/

Marianas Synopsis...
Satellite and radar imagery are showing mainly partly cloudy skies
and isolated showers. Localized pockets of scattered showers are
observed in the coastal waters well downwind northwest of the
islands. Locally buoys are indicating seas of 2 to 4 feet.

Discussion...
A surface ridge axis is firmly planted over the Marianas, situated
between the arms of the monsoon trough that are well north and south
of the islands. Generally isolated showers are expected through
tomorrow morning, with occasional pockets of scattered showers
developing offshore northwest of the islands. A subtle surface trough
looks to pivot around the western edge of the ridge and clip the
Marianas tomorrow. As a result, might see a slight uptick in clouds
and showers. Winds will also be slightly lower from the southeast
tomorrow. This could result in island-effect/enhanced showers and
possibly thunderstorms along the leeward side of the islands. Sunday
and Monday could see an increasing potential for island-effect
convection as the moisture profile trends up and winds become
lighter and more parallel to the islands from the south to southwest.
If upper-level cloud blow over builds overhead from convection down
in western Micronesia, this could limit the island heating needed for
convective buildups. As we head into next week, the ridge will
retreat and the south to southwest monsoon flow will increase,
bringing an elevated potential for showers and thunderstorms.

Marine/Surf...
Mainly gentle southeasterlies will prevail through Saturday, then
become light from the south and southwest for the rest of the
weekend. Winds will begin to pick up next week as the high pressure
ridge shifts east and the southerly monsoon flow increases, with
winds becoming gentle to moderate by midweek. Combined seas of 3 to 4
feet are expected through midweek, possibly increasing late next
week as a west to northwest swell emanating from a strengthening
tropical cyclone north of the Philippines passes through.

A moderate risk of rip currents will continue along east facing
reefs, with a low risk along all other reefs. Surf and rip risk could
rise by around midweek along north and especially west facing reefs
with the arrival of the aforementioned west to northwest swell.

Eastern Micronesia...
Periods of unsettled weather can be expected for eastern Micronesia
throughout the forecast period. Two major features are in the region
producing showers. The first is a robust trade-wind trough pushing
over RMI, and the other is a series of surface-level troughs between
Kosrae and Pohnpei.

The convection associated with the trade-wind trough has begun to
cycle downward, so showers are expected to be high-end scattered
over Majuro. This trough will later give way to a redeveloping ITCZ
that will keep Majuro wet for the majority of the forecast period.

The convection associated with the series of surface troughs is
producing low-end scattered showers for Kosrae and Pohnpei. A
temporary lull in showers is expected before the trough that is
currently over RMI moves to the west.

Combined seas are expected to remain fairly steady at 4 to 6 feet.
Winds overall are expected to remain light to moderate over the
forecast period with the exception that Majuro is expected to see
fresh winds tonight. This is due to the passing trough overhead.
Once it passes, winds will become light to moderate like the rest of
the region.

Western Micronesia...
Satellite this afternoon shows numerous showers and isolated
thunderstorms over the Republic of Palau, becoming scattered to the
east over much of Yap State including Yap Proper. An area of strong
surface convergence has set up over far western Micronesia within the
southwest to westerly monsoon flow across the region, with additional
enhancement from divergent flow aloft. The surface ridge near Yap
Proper has moved away to the northwest, and a surface trough has
moved in to take its place, enhancing convergence and shower
development over western Yap State and the ROP. This disorganized,
unsettled pattern will continue through at least Saturday as the
beginnings of a monsoon-like trough look to develop near Palau and
Yap. However, model guidance shows this weak trough shifting north of
the region by Sunday as a surface ridge builds near Palau, enabling
quieter conditions for the latter half of the weekend into early next
week. In the meantime, numerous showers are expected to continue
this evening for Palau with some locally heavy showers and stronger
gusts possible, gradually decreasing to scattered during the early
morning hours Saturday. Yap will remain east of the strongest
convergence and can expect scattered showers over the next day or so,
becoming isolated once more by Sunday.

To the east, drier conditions prevail over Chuuk with just isolated
showers and partly cloudy skies this afternoon. Patchy showers are
seen upstream as a subtle trough moves in from the east, and low-end
scattered (30 percent chance) showers were included in the forecast
for tonight. By Sunday, a more robust trough will have moved into the
area, possibly developing a weak circulation just west of Chuuk
Lagoon and maintaining scattered showers in the forecast until
Monday, when another ridge looks to move in.

Benign marine conditions continue. Mostly gentle to moderate
southerly to westerly flow will prevail for Palau and Yap through the
forecast period, but some fresh to even strong gusts could be
possible through the first half of the weekend near locally heavy
showers, especially near Palau. Chuuk can expect gentle to moderate
east to southeast winds through much of next week. Combined seas of
around 2 to 3 feet are expected to continue near Palau and Yap, and
around 3 to 4 feet for Chuuk.

&&

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

$$

Marianas Update: Williams
East/West Micronesia Update: Kleeschulte
Marianas: Slagle
East Micronesia: Bowsher
West Micronesia: DeCou