432
FXPQ50 PGUM 130711
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
511 PM ChST Sun Jul 13 2025

.Marianas Synopsis...
Satellite imagery shows mostly cloudy skies across the Marianas, but
most of the showers and thunderstorms associated with the feeder
bands/monsoon tail of Tropical Storm Nari (06W) have been slowly
drifting northward. Seas are around 4 to 6 feet, driven by the
primary trade swell, a weak secondary southwest swell, and gentle to
moderate southeast winds.

&&

.Discussion...
As distant Tropical Storm Nari continues to move north and way from
the region, so will the feeder bands/monsoon tail that extend south
and southwest from Nari. Already the Blended Total Precipitable
Water satellite product has shown PWATs decreasing from around 2.4 to
2.1 inches since this morning, indicating some drier air is moving
into the region. The lack of significant upper-level features is also
keeping the potential for thunderstorms limited and mainly northwest
of the Marianas, within the feeder bands that are pulling tropical
air into Nari. Expect drier weather tonight through Tuesday as the
lack of any significant surface features and drier air will allow
cloud cover to decrease and help to keep showers isolated.

Looking towards the latter half of the week, there is a TUTT cell
near Wake Island that will start to near the Marianas as early as
Wednesday, and across western Micronesia a developing monsoon trough
will slowly lift north to northwest over the next few days. Together
these features will increase moisture and instability across the
Marianas, leading to an increase in showers and thunderstorms.
However, how widespread and intense showers and thunderstorms will be
depends on the exact development of the monsoon trough and any
tropical disturbance that may develop with the trough, and how the
low-level dynamics of the trough line up with the upper-level
dynamics of the TUTT. Currently, the GFS and a portion of GFS
ensembles favors a more northern shift in the monsoon trough, which
places it under the TUTT as it nears the Marianas, leading to more
showers and thunderstorms, potentially being locally heavy at times.
The ECMWF and ECMWF ensembles pull the monsoon trough more northwest
and slightly west of the TUTT, which would still lead to showers, but
they would be more scattered and episodic in nature, along with
isolated thunderstorms. The Canadian and National Blend are currently
between the GFS and ECMWF, keeping confidence on either solution
fairly low. Overall, expect wetter pattern for the later half of the
week.

&&

.Marine...
Scattered showers and isolated thunderstorms are developing just west
of the coastal waters of the Marianas, along the feeder bands/monsoon
tail that extend from Tropical Storm Nari (06W). The potential for
showers and isolated thunderstorms are decreasing and will continue
to decrease through Tuesday as the feeder bands/monsoon tail are
pulled northward by TS Nari. Gentle to moderate 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 westerly swell
builds. A TUTT cell near Wake Island will near the Marianas later
this week, increasing the potential for thunderstorms. Around the
same time the monsoon trough in western Micronesia will lift north to
northwest, increasing the potential for showers across the region.

&&

.Eastern Micronesia...
Scattered to widespread showers are seen approaching Pohnpei and
Kosrae with stratiform rain across Majuro. North Point, Kalo, and
Utwe buoys show combined seas between 5 to 7 feet across the region.

The Inter-Tropical Convergence Zone (ITCZ) remains active across the
region. Widespread showers were seen across Majuro this morning,
which produced a wind gust of 36 knots in Majuro. The showers and
thunderstorms have generally stratified out over Majuro but some
stratiform rain will continue until the next batch of convection
further east moves in. The convergence that brought widespread
showers to Majuro has now shifted towards Kosrae. Numerous showers
this evening look to become widespread overnight with an occasional
gust to 30 kt possible near heavier showers. This feature looks to
move through Pohnpei tomorrow. There will be a brief break for
Pohnpei and Kosrae towards the middle of the week before the pattern
reloads. The long range pattern looks to remain active with a
combination of a trade-wind surge, the ITCZ, and a potential monsoon
trough all interacting over eastern Micronesia next weekend.

Combined seas are generally between 5 to 7 feet across the region.
Seas are expected to fall to 4 to 6 feet across Pohnpei and Kosrae
tonight. Additionally, both models and Kosrae`s buoy have picked up
on a weak southeast swell. With the decrease in combined sea heights
and a southeasterly swell, the easterly swell has fallen below High
Surf Advisory criteria across Kosrae and the High Surf Advisory was
allowed to expire.

For Majuro, the latest ASCAT shows a large swath of 25 to 30 kt
winds across the southern RMI and pockets of 25 kt winds further
east. The Small Craft Advisory was extended another 12 hours until 3
AM ChST due to the elevated winds. Seas could be especially
hazardous to small craft near heavy showers.

&&

.Western Micronesia...
A developing monsoon trough is the primary feature driving the
weather across Palau and Yap. Much drier conditions are currently in
place across both Yap Proper and Palau, however, this looks to be
short-lived. Models indicate a weak monsoon surge moving into the
region over the next few days. This is not yet evident on the latest
ASCAT analysis, with winds remaining around 5 to 10 knots across the
region. Based on current satellite trends, you can expect convection
to initially be isolated at both Yap Proper and Palau, slowly
increasing to scattered near midnight as winds pick up to around 15
knots over Palau. Bands of convection are seen to the west of Palau,
within the monsoonal flow. These bands are expected to move into both
Palau and Yap near midnight tonight. Over the next few days, models
are in fairly good agreement that a tropical disturbance will spin up
to the north of Yap Proper and Palau, though location and strength
remain questionable, varying from model to model. As this disturbance
develops, we can expect to see the aforementioned monsoon surge to
make itself known, increasing convection across the area. Decided to
keep POPs (Probability of Precipitation) at around 50 percent, though
models are indicated much higher POPs. These higher POPs are
dependent on the strength and location of the developing disturbance,
so until confidence in the expected pattern improves, will keep POPs
at the 50 percent range. Both Yap and Palau look to remain in a wet
monsoon pattern for the next several days.

For Chuuk, partly cloudy skies with spotty showers is currently in
place over Weno. This looks to change through the evening as a weak
trade-wind trough approaches from eastern Micronesia, pulling the
ITCZ along with it. There will then be a brief break in showers
Monday before another approaching trough interacts with the far
western end of an active ITCZ to create an overall unsettled pattern
that will continue through most of the week.

Other than with the showers and thunderstorms, marine conditions look
to remain relatively benign through the week. Seas of around 3 to 4
feet look to increase a bit for Palau and Yap as a small trade-wind
swell moves into the area, combining with the monsoon swell, to
produce seas of up to 6 feet at times. Depending on the strength of
the developing disturbance that is expected to the north, seas could
increase further. Gentle to moderate monsoon winds will continue
through the week at Palau and light to gentle winds will be
occasionally moderate at Yap. For Chuuk, seas could peak around 6
feet briefly around midweek, remaining at or below 5 feet otherwise.

&&

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

$$

Marianas: Schank
East Micronesia: Williams
West Micronesia: Kleeschulte