479
FXPQ50 PGUM 210934
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
734 PM ChST Fri Aug 21 2026

.Marianas Synopsis...
Satellite shows mostly cloudy skies across the Marianas and radar
shows scattered showers along outer rainbands of Tropical Storm
Saudel. Altimetry shows combined seas between 5 and 7 feet across
Guam and Rota and 7 to 10 feet across Saipan and Tinian.

&&

.Discussion...
Tropical Storm Saudel 17W is currently located near 15N148E, or 165
miles east of Saipan. Saudel is moving to the north-northwest at 9
mph. A Tropical Storm Watch remains in effect for Saipan and Tinian,
however, tropical storm conditions are not expected unless a
significant deviation to the west occurs within the next couple of
hours. The main concern for the short term are the outer bands of
Saudel. These showers and thunderstorms can produce locally very
heavy rainfall and frequent lightning. The outer bands are mainly
impacting Guam and Rota this evening, but as Saudel moves across the
far northern Marianas, the outer rain bands will trek across Saipan
and Tinian. Generally, 1 to 3 inches of rain is expected in the next
24 hours, but locally higher rainfall amounts will be possible.

As Tropical Storm Saudel moves northward, the southwest monsoon will
lift over the Marianas next week. Scattered to numerous locally
heavy showers will be possible through much of the week across the
Marianas. Heavy rainfall could lead to flash flooding and mudslides.
See the Hydrology section for more details.

&&

.Marine...
A Small Craft Advisory is currently in effect for Saipan and Tinian
Coastal waters until Sunday afternoon. Combined seas between 8 to 12
feet and winds of 20 to 30 kt will make marine conditions hazardous
to small craft. Choppy seas are expected across Guam and Rota through
the next few days. Seas could approach small craft criteria next
week as a monsoon surge develops. There is a High Surf Advisory along
north facing reefs of Saipan and Tinian until Sunday afternoon and a
high risk for rip currents along east facing reefs across all of the
Marianas.

&&

.Hydrology...
A monsoon surge is developing well south of Tropical Storm Saudel and
will lift northward across the Marianas late this weekend and into
next week.

Some uncertainty remains regarding potential rainfall impacts, but
early model ensemble guidance estimates suggest 4 to 8 inches of
rainfall falling Sunday night through Thursday across Guam and Rota,
and 3 to 7 inches across Saipan and Tinian. Locally higher amounts
will be possible, especially if the monsoon surge is stronger than
forecasted. Scattered to numerous locally heavy showers and isolated
thunderstorms will be possible through the week.

Residents on these islands need to closely monitor this developing
situation as flash flood watches, flood advisories and flash flood
warnings could be issued later.

&&

.Tropical Systems...
Tropical Storm Saudel (17W) is centered near 15N148E, just around 165
miles east of Saipan. Saudel is moving north-northwest at 9 mph, with
maximum sustained winds now at 70 mph near the center. This system
is expected to continue to barrel toward the far northern Marianas,
making a slight turn toward the northwest and move a little faster
come Saturday. By then, Saudel is likely to become a typhoon as it
passes over Pagan and Agrihan. While little change has been observed
in the storm motion the last few cycles, the center has wobbled
considerably to the west, which in addition an expanded wind field,
slightly increasing chances for TS winds to linger over Tinian and
Saipan coastal waters. Even so, the wide TS wind field is expected to
contract a little over the next 12 hours, leaving little room for
damaging winds to ensue across Tinian and Saipan. Even so, as a
precaution, a Tropical Storm Watch remains in effect for Tinian and
Saipan at this time. For the other islands affected, a Typhoon
Warning remains in effect for Pagan and Agrihan, meanwhile a Tropical
Storm Warning and a Typhoon Watch remain in effect for Alamagan.

&&

.Eastern Micronesia...
A broad tropical disturbance to the east of Majuro and a large
northwesterly inflow into the system are bringing unsettled weather
to Pohnpei, Kosrae, and Majuro. Scattered showers and isolated
thunderstorms are expected for much of the weekend, possibly becoming
numerous Saturday night or Sunday for Kosrae and Majuro with locally
heavy showers possible as well. The disturbance is expected to drift
north by Monday, potentially dropping precipitation chances back
down to scattered or even isolated by Tuesday. Gentle to moderate
northwesterly winds for Kosrae will continue and expand into Pohnpei
by tomorrow and continue for much of the forecast period. Meanwhile,
light and variable winds for Majuro today and will become moderate
to fresh south or southwesterlies Sunday before gradually easing
starting Monday night. Models indicate a dominant southerly swell for
all islands and a mix of smaller swells from pretty much all
directions. This is causing combined seas to be largest near Pohnpei
and Kosrae this weekend at around 5 to 7 ft.

&&

.Western Micronesia...
An intensifying monsoon surge along the southern peripheries of a
developing trough axis stretching from TS Saudel southwestward, is
expected to continue to enhance a disturbance just over Yap. Intense
showers and thunderstorms are expected to peak at Yap tonight and
Saturday, to then taper down slowly thereafter. Meanwhile at Palau,
the aforementioned disturbance will continue to induce a strong
convergence zone overhead, bringing more intense showers and
thunderstorms tonight and Saturday as well, followed by a slight
diffusion that may bring periods of dry spells thereafter.

Current rainfall estimates indicate 5 to 8 inches of rainfall in the
general vicinity of Palau over the next 36 hours, with slightly
lower amounts expected near Yap. Even so, these rainfall totals
remain highly uncertain due to the generally unsettled weather
pattern in the area, heavily reliant on how the disturbance over Yap
may move. Due to the aforementioned changes in the weather and sea
regimes, the Small Craft Advisory was extended for both Palau and Yap
through at least Sunday afternoon.

This pattern is not likely to taper down significantly until early
next week as a distant TS Saudel continues to pivot toward the far
northern Marianas. As such, the general public must continue to
monitor the forecast for any potential changes and/or developments
over the next several days. In the meantime, as the dominant
southwesterly swells induced by distant Tropical Storm Saudel
continue to weaken, along with a significant decrease in southerly
winds, sea conditions are no longer expected to be hazardous to small
craft beginning earlier in the day. Seas will remain just below 10
feet and remain choppy as various swells continue to mix in. As such,
a Small Craft Advisory was ended earlier for Chuuk coastal waters.
However, a significant south to southwest swell enhanced by distant
TS Saudel (17W) continues to produce hazardous surf along south
facing reefs tonight, so the High Surf Advisory was extended through
late tonight. Said swell is expected to decrease further over the
next few days, allowing surf to drop below hazardous levels by
sunrise on Saturday.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through Sunday afternoon for GUZ001.

MP...High Rip Current Risk through Sunday afternoon for MPZ001>003.

     Tropical Storm Watch for MPZ002-003.

Marianas Waters...Tropical Storm Watch for PMZ153-154.

     Small Craft Advisory until 5 PM ChST Sunday for PMZ153-154.

&&

$$

Marianas: Williams
East Micronesia: Ogle
West Micronesia/Tropical: Montvila