620
FXPQ50 PGUM 210811
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
611 PM ChST Tue Jul 21 2026

.Marianas Synopsis...
Satellite shows isolated to low-end scattered showers across the
Marianas this evening as weak shower bands from Invest 92W move
through. More scattered bands are expected tonight, mainly for Guam.
Winds today were mostly high enough to limit island effect and are
already starting to make a turn to the south over Guam. Altimetry,
buoy, and model data suggest combined seas are 4 to 5 feet.

&&

.Discussion...
The monsoon trough with imbedded Invest 92W to the southwest of the
Marianas continues to push occasionally scattered showers into the
region along with increasingly southerly winds. This disturbance is
expected to keep its distance and keep the Marianas dry overall for
the next few days, with the exception of increasing island effect
showers and thunderstorms. Guam may receive slightly more rainfall
due to its closer proximity to 92W. Light to gentle winds will slowly
drop off to light and variable winds tomorrow night. This will allow
island effect showers and thunderstorms to develop in the afternoon
through Saturday for Guam, Tinian, and Saipan. Winds may even be
light enough Thursday for Rota to recieve island effect showers.
Coverage will depend on how clear conditions are in the mornings. As
a shearline/cold front and the band of convergence near Chuuk
interact, this may increase the chance for precipitation over the
Marianas Wednesday night. However, this remains uncertain so isolated
showers and thunderstorms remain in the forecast. Afterwards,
overall shower coverage is expected to return to isolated over the
weekend, with isolated thunderstorms returning at the end of the week
as Invest 93W potentially approaches the Marianas.

&&

.Marine...
Light to gentle southeasterlies will prevail across the region
through early tonight, shifting south by midnight. Combined seas of
4 to 5 feet are expected to remain fairly steady with a slight
increase Wednesday possible depending on the monsoon surge to the
southwest. Otherwise, seas look to drop Thursday night. The main
swells are the dominant southwest swell, the weak easterly trade
swell, and a weak southeast swell. A moderate risk of rip currents is
in effect for south and west facing reefs. A fourth weak, but very
long period southeast swell is also possible sometime tomorrow.
Therefore, east reefs will need to be monitored for the potential to
reach a moderate risk of rip currents as soon as Wednesday night.
Isolated thunderstorms are possible through at least Friday, causing
a moderate risk of lightninig along coastlines.

&&

.Tropical Systems...
A very broad, weak disturbance has begun to take shape within the
monsoon trough north of Palau and Yap near 13N136E, now dubbed
Invest 92W by the Joint Typhoon Warning Center (JTWC). 92W is rated
"sub-low", meaning it is not expected to develop into a significant
tropical cyclone (a tropical depression) over the next few days, but
will continue to be monitored for development. Himawari visible
satellite imagery this afternoon shows an area of broad, flaring
convection within the convergence along 92W`s southern and eastern
flank, associated with the monsoon pattern feeding into it. Moderate
to locally heavy rainfall persisted over Yap through the morning,
but is beginning to break up this afternoon. While showers are also
fairly patchy to the southwest near Palau, locally heavy rainfall
will be possible at times through at least tonight as 92W shifts
northwestward. Over the next few days, Invest 92W looks to gradually
develop a very broad circulation over the Philippine Sea as it
meanders northwest, potentially exiting west of Guam`s Area of
Responsibility (AOR) by the end of the week, and potentially as a
tropical depression. Overall, 92W will help maintain a wet monsoon
pattern over far western Micronesia for much of the remainder of the
week.

Additionally, a weak disturbance is seen to the northeast of Majuro
Atoll near 12N178E, now dubbed Invest 93W by JTWC as of this
morning. 93W is also rated as a "sub-low", and development is not
expected over the next few days. Latest scatterometry data depicts a
small circulation here with 15 to 20 mph winds along its northern
flank, and a small embedded area of 25 mph winds associated with
nearby convection. There is another weak circulation nearby to its
southwest, located southeast of Majuro near 4N174E. CIMSS 850mb
vorticity analysis shows the stronger low-level vorticity is focused
around 93W, and models support slight consolidation around this area
over the next few days. At the same time, some of the vorticity near
Majuro looks to shift westward and away, potentially slowing the
development of Invest 93W somewhat as it meanders west-
northwestward.

&&

.Eastern Micronesia...
Fairly dry conditions prevail across eastern Micronesia as a
doldrum-like pattern begins to set up. The heavy showers associated
with the broad southeastward convergence near Pohnpei and Kosrae,
south of the monsoon trough, are shifting farther west. Only patchy
isolated to scattered showers remain, mainly between Majuro and
Kosrae, and southwest of Kosrae and Pohnpei. Meanwhile, a pair of
weak surface circulations persist over the eastern RMI and northeast
of Majuro, but skies are partly cloudy with only isolated showers
seen throughout the area, due to weak low-level forcing and light
surface winds. The circulation to the northeast is now dubbed Invest
93W by the JTWC, and is discussed in more detail in the Tropical
Systems section above. Models depict very slow development and
movement of 93W as it meanders northwest over the next few days,
skirting the far northern RMI, with very little to no direct impact
to eastern Micronesia. Wetter conditions resume toward the end of the
week, mainly for Pohnpei and Kosrae, as convergence increases across
the area along the far northern edge of a northward-lifting buffer
circulation.

Altimetry data shows combined seas between 3 and 5 feet across much
of the region, comprised mainly of a southeast swell emanating from
distant features in the Southern Hemisphere, with a light, secondary
west to south-southwest swell. Seas may see a gradual, slight
diminishing by the end of the week as swells subside.

&&

.Western Micronesia...
For Palau and Yap, a Special Weather Statement remains in effect
for the developing monsoon pattern and Invest 92W. These features
are producing up to fresh to strong winds with gusts up to near-gale
force over the next few days. Scattered to widespread locally heavy
showers are to be expected through at least Thursday. Model guidance
suggests 2 to 4 inches through Wednesday, and an additional 1 to 3
inches from Wednesday night through Friday, totaling 3 to 7 inches
by the weekend. If these showers develop as expected, soils will
become saturated enough to pose a risk for mudslides toward the end
of the week. At this time, the risk remains low. These features
will keep seas choppy near Palau and Yap but remaining below Small
Craft Advisory criteria (of sustained 22 knot winds and 10 ft seas).
As 92W, embedded within the monsoon trough, attempts to consolidate,
it will move north and carry the bulk of the convective monsoon with
it, easing the showers and winds near Palau and Yap as early as
Saturday.

For Chuuk, a band of convergence will produce scattered showers for
the lagoon for the next day or so. Then, a drier weather pattern is
expected to set up. Seas near Chuuk are expected to remain benign at
3 to 4 feet through the week.

&&

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

$$

Marianas: Ogle
East Micronesia: DeCou
West Micronesia: Bowsher