789
FXPQ50 PGUM 200837
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
637 PM ChST Thu Nov 20 2025

.Marianas Synopsis...
Satellite imagery shows partly cloudy skies over the Marianas and a
few isolated showers moving into the waters of Guam and Saipan.
Altimetry shows combined seas of 6 to 7 feet, while buoy data also
shows 6 to 7 foot sea heights. A high risk of rip currents remains in
effect. A Small Craft Advisory has been issued for Friday through
Saturday.

&&

.Discussion...
The forecast only needed minor tweaks for the forecast period.
A trade-wind surge is pushing through the region. There is also some
upper-level support as a upper-level low persists over the far
northern CNMI. These two features interacting will produce waves of
showers and thunderstorms over the next few days. Once these
features move westward, conditions will return to pleasant but
windier weather.

&&

.Marine...
Moderate to fresh trade winds are expected throughout the week.
Combined seas of 6 to 8 feet are expected to increase up to 10
feet Friday. With seas expected to reach 10 feet and winds expected
to approach 22 knots with higher frequent gusts, a Small Craft
Advisory was issued for Friday through Saturday. Seas are expected to
begin tapering down Sunday through early next week. A high risk of
rip currents along east facing reefs, and a moderate risk of rip
currents along north facing reefs, are expected for at least the rest
of the week as elevated trade swell lingers. A moderate risk of
lightning is expected beginning Friday.

&&

.Eastern Micronesia...
Pohnpei:
As expected, the trade-wind surge to the north has strengthened,
expanding north and south to be centered between 8N and 17N from 150E
to the Date Line. This occurred as high pressure to the north
(currently located east of Japan) tightened the pressure gradient.
This allowed maximum sustained winds to peak at 30 knots as seen on
the overnight scatterometer plot, with sustained 25 knots having
crept southward into Pohnpei`s waters. This orientation of the trade
surge and progression of the high to the north suggest advisory
criteria wind gusts will continue through late Saturday afternoon.

As such, a Small Craft Advisory for frequent wind gusts of 25 to
perhaps 30 knots can be expected. This would be most probable during
heavier downpours tonight (Locally heavy rainfall was added to the
forecast), as the morning balloon launch sampled 35 knots just above
the surface. The increased resultant wind waves and northeasterly
swell will pose a high surf concern for at least northern reefs, and
possibly eastern reefs if the winds/gradient strengthens more. With
that in mind we opted to include eastern reefs as well, despite if
falling short of criteria currently (12 ft for east reefs, 9 feet all
other reefs) just to account for any potential increase. If this
fails to develop, we could always remove eastern reefs from the
headline, but for now given just enough confidence for this to occur,
especially as tidal influences potentially come into play, the east
inclusion made sense. Otherwise, look for scattered showers and
isolated thunderstorms to persist through early next week.

Kosrae and Majuro:
Given Kosrae has a lower threshold of 8 feet for east facing reefs,
and 9 feet for northern reefs, with 6 to 7 foot swells at 8 to 9
seconds being enough to reach hazardous conditions, hoisting the
High Surf Advisory for Kosrae was an easy call. With that said, we
were tempted to hoist them for Majuro, but given the swell doesn`t
build far enough east (the trade surge) until Friday night or
Saturday (as the high pressure system north of us slides further
east, allowing the pressure gradient to increase by then), we opted
to not issue the headline yet with it being a 3rd through 5th
forecast period potential event, holding off for now seemed sensible.
However, Majuro may need to be added later, especially if later
PacIOOS data shows the tidal surge possibly becoming more of a
concern. Otherwise, scattered showers will persist through the
forecast period.

&&

.Western Micronesia...
A broad, robust trough is seen just east of Chuuk waters, with
scattered to numerous showers seen across much of the region from
Chuuk eastward to the Marshall Islands. Scatterometry from this
morning reveals a broad area of 20 to 25 kt winds across this area
just upstream of Chuuk extending eastward into the Marshalls, from
around 8N to 15N, along the southern periphery of a broader trade-
wind surge. These higher winds are expected to reach Chuuk tonight as
the leading edge of the trough and associated showers move west
through the area, and near-gale to gale-force gusts will be possible
with the heaviest showers. A Small Craft Advisory has been issued
through 5 AM ChST Friday, as winds are expected to quickly relax
below hazardous levels thereafter. The Small Craft Advisory may need
to be extended if these stronger winds are delayed or persist longer
than latest model guidance indicates. Numerous showers are expected
to continue Friday along the backside of the exiting trough as it
interacts with the Near-Equatorial Trough (NET) situated over Yap
State. Showers will then gradually diminish for Chuuk Friday night
through the weekend as this broader disturbance moves westward
across Yap State.

Relatively dry conditions continue tonight across far western
Micronesia with just isolated showers seen near Yap and Palau. This
dry weather will be short-lived as a broad disturbance takes shape
within the NET just southeast of the region as it interacts with the
trough moving in from over Chuuk. Model guidance depicts a broad,
elongated circulation gradually taking shape and meandering northwest
across Palau and Yap through the weekend, exiting west of the region
around Monday morning. Numerous locally heavy showers and isolated
thunderstorms are expected across the region as the disturbance moves
through, with most of the showers and gustier winds expected for Yap
Proper, mainly Saturday through Sunday. Ensemble model guidance
indicates Yap could see 2 to 4 inches of rain from Friday through
Sunday night, with a possible 1 to 3 inches for Palau. Sustained
winds near Yap may approach levels hazardous to small craft around
Saturday night through Sunday night, and will be closely monitored
for the possibility of a later issuance. Overall, the timing of
showers and thunderstorms with the passage of this developing
disturbance remains uncertain, and Probability of Precipitation (PoP)
may see significant changes in the forecast over the next day or so.

There was little to no change in the marine forecast. Altimetry data
indicates combined seas of 4 to 6 feet near Palau and Yap, and around
5 to 8 feet near Chuuk. Gentle to moderate winds are expected for
Palau with moderate to fresh winds for Yap and Chuuk for much of the
forecast period. There is currently a Small Craft Advisory in effect
for Chuuk until 5 AM ChST Friday. Even after the Small Craft Advisory
expires, elevated gusty trade winds and elevated trade swell will
maintain choppy sea conditions through the weekend, for both Chuuk
and Yap.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through late Monday night for GUZ001.

MP...High Rip Current Risk through late Monday night for MPZ001>003.

Marianas Waters...None.
&&

$$

Marianas: Bowsher
East Micronesia: Doll
West Micronesia: DeCou