151
FXPQ50 PGUM 140710
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
510 PM ChST Mon Jul 14 2025

.Marianas Synopsis...
Satellite imagery shows mostly cloudy skies across the Marianas, with
isolated showers near the islands. Scattered showers are starting to
develop to the west and south of Guam, along convergent flow north
of the monsoon pattern across western Micronesia. Seas are around 4
to 5 feet, driven by the primary trade swell, a weak secondary
westerly swell, and gentle to moderate east to southeast winds.

&&

.Discussion...
So far showers have been fairly isolated across the Marianas, but as
the previous forecast mentioned, convergent flow is increasing near
the Marianas, mainly west and south of Guam this evening. This has
lead to an increase of showers over the past few hours southwest of
Guam, and this area of convergence is starting to lift northward,
which should cause scattered showers to move into the Marianas
tonight and potentially into Tuesday as a trade-wind trough east of
the Marianas will likely move near the Marianas Tuesday. Still not
expecting any thunderstorms to develop tonight or Tuesday, but the
TUTT cell west of Wake Island continues to slowly drift westward and
is still expected to reach the Marianas around Wednesday or Thursday,
increasing the potential for thunderstorms. Model guidance also
continues to move the monsoonal pattern across western Micronesia
closer to the Marianas late this week which will also promote a wet
pattern for the Marianas. Since yesterday, the GFS has trended
slightly towards the ECMWF, which pulls the monsoon trough slightly
more northwest, suggesting showers will be more scattered and
episodic in nature, but there is still some uncertainty in the actual
develop of the monsoon trough and overall pattern, so exact details
such as timing of these showers and what days may see the most rain
will be difficult to pinpoint for later this week and into early next
week.

&&

.Marine...
Expect scattered showers to develop across the coastal waters
overnight as convergent flow southwest of Guam shifts northward.
Gentle to moderate east to southeast winds will continue across the
region for most of the week, with seas of 4 to 6 feet building to 5
to 7 feet by Thursday as the west-southwest swell builds. A TUTT cell
near Wake Island and a monsoon trough in western Micronesia are
slowly moving towards the Marianas and will be increasing the
potential for showers and thunderstorms starting as early as
Wednesday.

&&

.Eastern Micronesia...
Scattered showers are seen across Pohnpei, Kosrae, and Majuro with
numerous showers seen across and south of Kwajalein and south of
Pohnpei. Buoy and altimetry data across eastern Micronesia shows
combined seas generally between 5 to 7 feet with a few isolated 8
foot seas apparent on altimetry data.

Conditions across eastern Micronesia have quieted some as the
widespread showers over Pohnpei have stratified out. Scattered
showers are present across much of the region. Shower coverage looks
to stay low to medium (30 to 40%) scattered through tomorrow for
Majuro and through Thursday for Kosrae and Pohnpei. Towards the end
of the week, convection is forecast to increase across the region as
trade-wind convergence increases and the ITCZ pulses back up.

Combined seas are generally between 5 and 7 feet, but altimetry has
picked up on some localized 8 foot seas, especially across the RMI.
The Small Craft Advisory has been cancelled for Pohnpei. The latest
scatterometer data shows winds have fallen below 22 knots with
pockets of 15 to 20 knot winds remaining. Choppy seas will remain
possible where heavier showers occur. Combined seas are forecast to
fall the next few days with seas falling to 3 to 5 feet later this
week.

&&

.Western Micronesia...
Not much changed in the reasoning behind the forecast for western
Micronesia. For Yap and Palau, The monsoon trough remains the main
player in the forecast. For tonight, a band of numerous showers and
isolated thunderstorms is in place across Palau and looks to remain
over the Republic through the night. Monsoon flow is spreading this
convection northeast toward Yap Proper. Therefore will maintain
numerous showers and isolated thunderstorms across Palau for tonight,
with isolated showers increasing to high-end scattered showers and
isolated thunderstorms for Yap. For the next few days, everything
depends on what actually occurs over the region. The latest model run
shows all models still in agreement that a circulation will develop
over the Philippine Sea north of Yap and palau. What remains
questionable is the strength and actual location of the disturbance.
The GFS remains the most aggressive, though it has come more in line
with the other models. The GFS also keeps the circulation farther
east, while the Canadian, ECMWF and NBM are all farther west. Since
most of the models are now showing a monsoon surge into Yap and Palau
as this disturbance develops, decided to increase shower coverage to
numerous at Palau Tuesday night and Wednesday for Yap, with the
mention of gusts and possible locally heavy showers. Current
guidance does keep the heavier rainfall amounts north of both Yap
Proper and Palau at this time. Regardless of the development of the
circulation, the expected surge and continued monsoon pattern looks
to maintain a wet pattern across Palau and Yap for the next several
days.

For Chuuk, numerous showers are seen to the east, pushing toward
Weno. Expect these showers to move into Weno later this evening.
Mostly just showers are evident with the trough, though instability
remains high enough to add isolated thunderstorms to the mix. As this
trough approaches, it will pull the western end of an ITCZ into the
area. There is also a weak Near-Equatorial Trough (NET) seen to the
south of Weno. These features will interact to maintain numerous
showers across Chuuk through Tuesday afternoon. Afterward, the NET
and ITCZ look to slowly weaken across Weno, allowing showers to
decrease a bit, though POPs look to remain in the 30 to 50 percent
range into the weekend.

No changes were made to the marine forecast. Seas will be a bit
rough at times with the strong gusts associated with the showers and
thunderstorms over all three locations.

&&

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

$$

Marianas: Schank
East Micronesia: Williams
West Micronesia: Kleeschulte