897
FXPQ50 PGUM 010910
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
710 PM ChST Sat Nov 1 2025

.Marianas Synopsis...
Satellite imagery shows partly cloudy skies that suggest isolated
showers over the Marianas. Altimetry shows combined seas of 6 to 8
feet, while buoy data shows about 6 feet.

&&

.Discussion...
An unsettle wet pattern is expected for this week. This is due the
the convergences zone produced by invest 98W over the weekend and 99W
during next week. The convergence zones is weakening over the
Marianas as 98W moves further away into the Philippine sea. This zone
is expected to producing scattered showers over the the region.

Invest 99W is currently a weak circulation near 12N147E southeast of
Guam. It is embedded in a monsoon trough that is extending from 98W
and between FSM and Guam to near 10N150E. This trough will likely
produce multiple spinners over the course of next week and the models
are having a hard time deciding which spinner is "the one". Whether
it is 99W or another invest, heavier showers and near gale winds are
possible with the peak anticipated to arrive around Wednesday to
Thursday. Then, the shower are expected to gradually taper down
starting around the end of next week.

&&

.Marine...
The outer edge of a trade-wind surge has moved into the Marianas,
bringing moderate to fresh winds and combined seas of 6 to 8 feet.
These conditions are expected to persist through the week. The
trade-wind surge could be enhanced by a circulation from Invest
99W, which could lead to conditions hazardous to small craft for
portions of the Marianas later in the week. There will be a moderate
risk for rip currents along north and east facing reefs through at
least the weekend.

&&

.Hydrology...
Short term...
Invest 98W, is centered north of Yap Proper near 10N136E. Model
guidance shows 98W`s convergence zone from the trade winds is
directly over the Marianas. This will force a tightening of the
streamline winds and consequentially bring in heavier showers to the
region. As 98W moves further into the Philippine Sea, so to will this
convergence zones move with 98W.

Long term...
The models are poorly handling 99W. Currently, GFS is locked on to a
small "spinner" that has little to no convective activity with it
near 12N147E, and the ECMWF has a east-west trough. This "spinner"
is part of the monsoon trough that is extending from 98W eastward
between FSM and Guam. This will be the breeding grounds for multiple
"spinners" over the next few days and one of them will be the one
that actually becomes something. Timing, location and intensity, are
still in a great deal of flux.

There is potential for Guam and the CNMI to see rainfall amounts of
3 to 7 inches from Sunday night through Thursday night, though
locally higher amounts will be possible. This rainfall is expected
to produce minor flooding across the islands, with flash flooding
possible in areas of heavier rainfall, especially over Guam.

&&

.Tropical Systems...
A developing disturbance, Invest 98W, is centered just southeast of
Yap Proper near 10N136E, moving slowly north-northwest. 98W is now
the subject of a Tropical Cyclone Formation Alert (TCFA) by the Joint
Typhoon Warning Center (JTWC). This means that Invest 98W is
expected to become a significant tropical cyclone (Tropical
Depression) within the next 24 hours. 98W is becoming more organized
and is in an area of favorable conditions for development. Model
consensus favors the invest becoming a tropical depression over the
Philippine Sea just north of Yap Proper. Further development is
expected as it moves west-northwest across the Philippine Sea. Invest
98W will be monitored closely over the next couple of days as it
moves through Yap Proper. Residents in northwest Yap State and
northern Palau should continue to monitor forecasts for any changes,
watches, warnings or advisories. For more information on Invest 98W
and the TCFA, see bulletins issued by JTWC under WMO headers ABPW10
PGTW and WTPN21 PGTW. There is also a Special Weather Statement for
Yap and Palau issued by the National Weather Service under WMO header
WWPQ82 PGUM.

Another weak disturbance, Invest 99W, is centered southeast of Guam
near 12N147E, moving west-northwest. 99W remains very disorganized
with only a weak circulation evident on the latest visible satellite.
Very little convection is seen with 99W. The likelihood of Invest
99W becoming a significant tropical cyclone within the next 24 hours
remains low. Latest model guidance does not favor development of this
little spinner and it looks like another circulation may develop
along the monsoon trough as it spreads over the region. This area
remains active and will be watched closely for any development over
the next few days. For more information on Invest 99W, see bulletins
issued by JTWC under WMO header ABPW10 PGTW.

&&

.Eastern Micronesia...
The drier trend continues across most of eastern Micronesia. A
trade-wind trough seen to the north of Kosrae looks to bring
scattered showers and isolated thunderstorms to Pohnpei Sunday into
Sunday night. The main feature affecting the region remains the
disturbance over and east of the Marshall Islands. A west-east
oriented trough extends from a very weak circulation southwest of
Kwajalein to a more pronounced circulation east- southeast of Majuro,
near the Date Line. As this trough progresses west, the weak
circulation looks to dissipate while the trough and more robust
circulation strengthens slightly. This system looks to bring
increasing convection to Majuro by Sunday night. Meanwhile, a weak
trade-wind trough looks to move into Pohnpei and Kosrae Monday night
into Tuesday, bringing a brief period of scattered showers and
isolated thunderstorms to both locations. Later in the week, the
disturbance over the Marshalls looks to approach Pohnpei and Kosrae,
bringing another round of increased convection. As this feature moves
out of the Marshalls, the Inter-Tropical Convergence Zone (ITCZ)
looks to redevelop and strengthen westward as a surge of trade winds
move through. This will result in convection continuing at Majuro
through the end of the week.

For the marine forecast, no major changes were needed. For Kosrae
and Pohnpei, combined seas of 3 and 5 feet and light to occasionally
gentle winds look to continue through the middle of next week Winds
are then expected to become gentle to moderate for the end of the
week. For Majuro, light to gentle winds look to become gentle to
moderate around the middle of next week. Combined seas of 3 to 5
feet will begin to build early next week, reaching 6 to 8 feet
around midweek as a northeast trade swell builds due to a trade-wind
surge.

&&

.Western Micronesia...
Invest 98W is located north of Yap as confirmed by visible satellite
imagery and surface observations at Yap. It remains the subject of a
TCFA (Tropical Cyclone Formation Alert), meaning the formation of a
tropical cyclone (of at least depression strength) is likely within
24 hours. In fact, recent visible and infra-red satellite imagery
shows rapid cloud development over Yap and to the south as
significant cloud top cooling is underway. A sudden burst of
lightning has coincided with this indicating a strengthening phase is
underway, with 98W likely becoming a tropical depression in the next
few hours.

Locally heavy rainfall and convective wind gusts in the 25 to 30 knot
range have already occurred and remain probable at Yap, and to a
lesser extent Palau. This potential will continue through Sunday.
Then, as 98W moves away, an active pattern will keep at least
scattered showers and isolated thunderstorm probable into the first
half of next week.

As for marine conditions, we were contemplating hoisting a Small
Craft Advisory for Yap, but the peak of gusts has already occurred
when only one observation hit 25 knots and Yap, with the remained in
the 19 to 22 knot range today there, which is very marginal for the
22 knot threshold part of criteria for such an advisory. Given that
the system is moving away from the region now and only a gradual
strengthening is expected over the next 36 hours, we decided to hold
off on issuing the headline. Seas also remain below 10 feet negating
the need for such.

Note: A Small Craft Advisory is issued when we expect one of the
following (or more) for a prolonged period of time - frequent gusts
to 22 knots, sustained winds of 22 knots, or 10 foot seas to issue
the advisory.

Otherwise, look for Gentle to strong winds to persist through the
forecast period, with higher convective gusts probable. Seas will
hold in the 5 to 6 foot range.

&&

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

$$

Marianas: Bowsher
East Micronesia: Kleeschulte
West Micronesia: Doll