023
FXPQ50 PGUM 111957
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
557 AM ChST Sat Jul 12 2025

.Marianas Update...
Satellite shows scattered showers moving southeast to northwest
across the region with locally heavy showers over the CNMI early this
morning. No major updates were needed in the short-term forecast.
Mid- to high-end scattered showers, possibly heavy at times, will
persist through this afternoon. Model guidance suggests that
overall convection may shuffle around tonight as the flow between
Tropical Depression 06W and a monsoonal pattern remains a bit
unorganized and may see some breaks in showers over Guam and Rota,
but may see showers linger a little longer over Tinian and Saipan.

Buoy and altimetry data reveal seas have increased to between 4 to 6
feet, comprised of trade swell and minor southwest swell.

&&

.Tropical Systems Update...
The center of loosely defined Invest Area 94W is not too far away
from Yap, near 10N140E. While it is being monitored for such
consideration, it is currently not suspect for development of a
tropical cyclone. It will likely move west or west-northwest, and be
clear of Micronesia before becoming a TC, with the possibility of
course, that it might never become one.

&&

.Eastern Micronesia Update...
With a well developed slug of moisture passing just south of Kosrae
and curving toward Pohnpei, raised the PoP`s a little for Pohnpei for
today and tonight. Pohnpei is now widespread today and high end
numerous tonight, then settles back into scattered showers for next
week. Also raised the PoP`s at Kosrae to high end numerous today as
that mass of showers and thunderstorms passes, then met up with the
previous forecast from tonight onward, so scattered showers through
Tuesday then isolated on Wednesday. At Majuro, no change today, but
decreased to 40 percent. Afterward, Majuro remains scattered to
numerous in shower coverage through Wednesday, so once again a wet
week for Eastern Micronesia.

At Pohnpei and Kosrae, seas of 6 to 8 feet today will gradually
diminish to between 4 and 6 feet by Wednesday. Winds of 10 to 20
knots will lower slightly to between 5 and 15 knots, while the gusts
will disappear. For Majuro, seas will start at 6 to 9 feet then
diminish to between 5 and 7 feet. Winds will maintain at about 10 to
20 knots. These conditions can be challenging for small craft,
especially the seas being just below 10 feet. If in doubt, don`t go
out!

&&

.Western Micronesia Update...
Did some trimming of PoP`s in Western Micronesia, based mainly on
satellite presentation. Koror was 70 percent today and 60 percent
tonight, now they are both 40 percent. No cold cloud tops left, just
medium gray. Afterward scattered showers the rest of of the week
until numerous on Wednesday as a monsoon surge could start to build
in. Same general story at Yap, they were numerous locally heavy, but
now after all the showers blew out, just medium gray left on the
satellite image. After tonight, scattered to numerous through the
midde of next week, more numerous than scattered. At Chuuk, both
today and tonight were numerous, but now Chuuk hardly even has any
medium gray clouds, plenty of open ocean though. Just took it down to
scattered for today and tonight, if the new trend holds, it can be
reduced more later.

At Koror, seas will be steady at 4 to 6 feet through the period.
Winds will be 10 to 20 knots for the same time period. For Yap, winds
will be 5 to 15 knots through Tuesday, then build further as the
potential monsoon surge sets up nearby. Within the Chuuk Waters,
winds will be 5 to 15 knots through the period. Seas of 5 to 7 feet
will gradually subside to between 4 and 6 feet.

&&

.Prev discussion... /issued 609 PM ChST Fri Jul 11 2025/

Marianas Synopsis...
An unsettled gentle to moderate southeast flow continues across the
Marianas as Tropical Depression 06W develops on the northern edge of
the region just north of 25N140E, and a monsoonal pattern develops
across western Micronesia. This unsettled pattern is producing
mostly cloudy to cloudy skies, scattered showers, and some short-
lived thunderstorms. Seas are around 4 to 5 feet, driven by the
primary trade swell and weak secondary southwest swell.

Discussion...
The Marianas is currently wedged in-between two large-scale weather
systems, with TD 06W to the northwest near 25N140E and the developing
monsoon trough across Palau and western Yap State, feeding moist
tropical air into the Marianas. If there were any significant surface
features such as a trough or circulation, this setup would be
supportive of heavy rain and potentially some flooding. However, due
the lack of strong surface features and weak subsidence aloft,
showers have been fairly scattered across the region with only a few
short-lived thunderstorms seen well west of Guam today. This overall
pattern is expected to continue through the weekend and into early
next as TD 06W and the monsoon trough shift north and then slowly
northwest the next few days, with a slight increase in showers
expected Saturday and Saturday night as a weak trough moves through
the Marianas. Looking towards the middle of next week, the area of
moist tropical air is expected to shift westward while the monsoon
trough is expected to shift northwest, as a broad circulation
develops south of Japan. The GFS keeps the Marianas within the
eastern edge of the tropical airmass which would continue to support
some increased cloud cover and showers through the week. The ECMWF,
however shifts the tropical airmass far enough west that some drier
air near Wake Island is able to move into the Marianas, which could
lead to slightly less cloud cover and help to limit the potential for
showers as well. Either scenario is possible but is will largely
depend on how TD 06W northwest of the Marianas and the monsoon
trough in western Micronesia develop over the next few days.

Marine...
Moist, gentle to moderate southeasterly flow extends across the
region as seas are around 4 to 5 feet near and east of the Marianas,
according to data from Ipan buoy and satellite altimetry. Gentle to
moderate south to southeast winds, scattered showers, and isolated
thunderstorms are expected to continue through the weekend and early
next week as Tropical Depression 06W, which developed just north of
the region today, and the developing monsoon trough in western
Micronesia continue to push moist air into the Marianas. Combined
seas will build to around 4 to 6 feet as the trade swell and
southwest swell build slightly this weekend. As the monsoon trough
continues to develop in western Micronesia, the southwest swell will
slowly build and increase seas and surf along south and west facing
reefs next week, but not expecting hazardous seas or surf to develop
over the next few days.

Tropical Systems...
The monsoon disturbance formerly designated by the Joint Typhoon
Warning Center (JTWC) as Invest 93W has been upgraded to Tropical
Depression (TD) 06W. TD 06W has shifted slightly north of the Area
of Responsibility (AOR) with its center near 25.2N 140.0E as of this
evening, and models are in good agreement on a continued northward
track. However, the trailing monsoon flow will continue to impact
much of the Marianas and western Micronesia.

To the south, JTWC is now monitoring another monsoon disturbance,
Invest 94W, located roughly 300 miles southeast of Yap near 7N142E.
Invest 94W is currently designated as a sub-low, meaning development
is very unlikely in the next 24 hours. Deterministic and ensemble
model guidance depicts a gradual north to northwestward shift of this
disturbance over the next few days, with very little organization or
development.

Eastern Micronesia...
An Inter-Tropical Convergence Zone (ITCZ) remains active across
eastern Micronesia this afternoon. Scattered to numerous showers and
isolated thunderstorms are found from east of Majuro, across Kosrae
to Pohnpei. The main changes to the forecast were to increase POPs
(Probability of Precipitation) for all three forecast points tonight.
Pohnpei and Kosrae were increased to 60 percent (numerous) while
Majuro remains scattered, although POPs were increased from 30
percent to 50 percent. The ITCZ is interacting with a weak trade-wind
trough near Pohnpei which is increasing the convection over Pohnpei
as it moves through the region. Beyond this trough, latest model
guidance shows weak troughs traversing the ITCZ over the next few
days, maintaining active convection through the middle of the coming
week. Shower coverage looks to vary through the period, with Pohnpei
and Kosrae seeing POPs in the 60 percent range tonight and into the
weekend, with Majuro seeing mainly from 30 to 50 percent until late
in the weekend, when POPs peak there at around 60 percent. Localized
heavy showers and fresh to near-gale gusts are possible with the
heavier showers and thunderstorms. The ITCZ does look to begin to
break down early next week, with POPs dropping to around 20 percent
at Kosrae around the middle of next week, and at Pohnpei and Majuro
later in the week.

Marine conditions don`t look to change much over the next few days.
Moderate to fresh winds are expected at Majuro through at least next
Wednesday. Pohnpei and Kosrae will see winds subside from moderate to
fresh, becoming gentle to moderate over the weekend. Pohnpei and
Kosrae buoys show seas between 5 and 7 feet, while altimetry shows 5
to 8 feet. For Majuro, Kalo buoy shows seas of 6 to 7 feet, with
altimetry matching pretty well, with 5 to 7 feet. The trade-wind
swell remains high enough to maintain hazardous surf conditions along
east facing reefs of Kosrae through Saturday night.

Western Micronesia...
An unsettled weather pattern persists across the region as the
southernmost axis of the monsoon trough extends across the Republic
of Palau and Yap State. Along the eastern extent of this trough
axis, JTWC is now monitoring a monsoon disturbance designated as
Invest 94W. Invest 94W is highly disorganized and models depict very
little development over the next few days, but it may help in
maintaining an active monsoon weather pattern across western
Micronesia through the weekend. Satellite late this afternoon shows
scattered to numerous showers and isolated thunderstorms across the
region, with the greatest coverage focused over southwest Yap State.
Showers have been increasing further west across the Republic of
Palau this afternoon with some heavier showers developing just south
of Koror. Periods of heavy showers and thunderstorms are expected to
continue for Palau and Yap into next week as a monsoon gyre tries to
form just north of the region. Timing is still somewhat uncertain,
but the developing pattern would likely maintain a stronger monsoon
flow and a very wet pattern into the end of next week. In the
meantime, winds will be mostly gentle to moderate out of the
southwest, with occasional fresh to strong gusts near heavier
showers.

For Chuuk, conditions have been relatively quiet this afternoon with
just isolated showers near Weno. However, shower and thunderstorm
coverage are expected to increase tonight through much of the
weekend as the western extent of the ITCZ interacts with the
broader monsoon pattern downstream, with numerous locally heavy
showers expected at times. Showers will then temporarily diminish
around Monday as a surface ridge sets up in the area, before another
disturbance arrives around midweek.

There was little change to the marine forecast. Buoy and altimetry
data indicate combined seas around 3 to 5 feet near Palau and Yap,
and 4 to 6 feet at Chuuk. Seas may see an increase near Palau and Yap
mid- to late next week in response to an increase in southwest swell
and wind waves. However, this will depend on how the overall monsoon
pattern develops north of the region next week so there is some
uncertainty in intensity and timing. Sea heights will see a very
slight decrease for Chuuk early next week with an easing of trade
swell.

&&

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

$$

Marianas Update: Cruz
Micronesia/Tropical Update: Stanko
Marianas: Schank
East Micronesia: Kleeschulte
West Micronesia/Tropical: DeCou