100
FXPQ50 PGUM 171925
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
525 AM ChST Tue Nov 18 2025

.Marianas Update...
Mostly dry weather remains on tap the next few days across the
Marianas as a trade-wind pattern remains firmly entrenched across teh
region. A few showers will move through, perhaps with even a very
small chance for a flash of lightning or two, based on satellite
imagery showing a few towering cumulus in the surrounding waters.
These towering cu are relatively short-lived due to their lower cloud
bases outrunning their higher cloud tops due to weaker winds aloft.
Winds will increase late week as a trade surge develops in the
region. This will also bring increasing showers and a higher chance
of thunderstorms between Thursday night and Saturday night. On the
waters, seas will begin to increase around Thursday and could reach
hazardous levels of 10 ft around Friday.

&&

.Eastern Micronesia Update...
Fairly quiet conditions are seen across all 3 locations early this
morning though showers and thunderstorms are found just south of
Kosrae. Short term dryness is on tap for Pohnpei and Majuro, but
showers south of Kosrae will spread north later today. Convection is
generally expected to spread over Pohnpei and Majuro in the coming
days as a broad west-moving trough pushes the east-west band of
showers and thunderstorms northward. Though models stop short in
indicating strong gust potential with heavier showers nearer the 3
main islands, there is some potential for strong gusts to around 30
kt in the northern atolls the next couple of days due to the
influence of an upper-level low near 14N169E. At the moment,
satellite imagery shows slow-moving thunderstorms just east of
Utirik that are producing quite a bit of lightning, and likely some
notable gusts. Seas of 5 to 7 ft are largely expected through the
week, a mix of a dominant trade swell and smaller north swell.
Increasing trades late week will add some chop to seas and will come
close to becoming hazardous to small craft. Additionally, with the
upcoming new moon phase, high tides will run a little higher so
increased surf could result in increased shore-side runup and
splashing along windward shores.

&&

.Western Micronesia Update...
The near-equatorial trough remains south of all 3 locations though a
westward-moving trade-wind trough is passing by Yap and Palau early
this morning. After several hours of late night thunderstorms, Yap is
starting to see a quieting trend with drier weather set to arrive by
midmorning. For Palau, tweaked down the rainfall potential and
slightly delayed the onset of showers to later today based on what is
expected to be a temporary convective stabilization for the morning.
Drier trades have punched into the Chuuk area and will continue to
dominate until Wed-Wed night as a trough brings stormier and gusty
weather. Drier conditions will spread to Yap and Palau by midweek,
lingering until around Friday as the next surface trough arrives.
Marine forecasts still look good with seas of 4 to 6 ft across the
region with a late-week increase in trade-wind swell. Additionally,
Yap and Palau could start to see an increasing north swell between
Thursday and Friday. Wave models keep the north swell small, but will
be one to watch in the even the north swell could build to 4 or 5 ft,
and ultimately more notable for shores facing north or west.

&&

.Prev discussion... /issued 524 PM ChST Mon Nov 17 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 5 to 6 feet, while buoy data also
shows 5 to 6 feet sea heights.

Discussion...
A pleasant week is in store for the Marianas. The time heights show
a deep dry pocket is expected to remain over the area through about
Thursday. This will inhibit showers from forming. Winds are expected
to be around 15 to 20 mph over the week, just below breezy
conditions. Around the weekend a passing trade-wind trough is
anticipated to move through bringing a slightly higher chance of
showers to the islands. To reflect this low-end scattered showers are
anticipated for Friday. Once this trough passes pleasant weather is
anticipated to return.

Marine...
Moderate to fresh trade winds are expected throughout the week.
Combined seas of 5 to 7 feet will remain steady through tonight,
then begin to gradually increase as the trade swell builds,
potentially reaching 7 to 9 feet by Thursday night. Seas and winds
could increase further on Friday and into the weekend as a trade-
wind surge builds across the region. This surge may become hazardous
to small craft, with seas nearing 10 feet and winds nearing 22 knots.
There will be a moderate risk of rip currents along north and east
facing reefs of the Marianas through at least Wednesday night. Then,
the trade swell is expected to build for the rest of the week. This
will allow the risk of rip currents to increased to high.

Eastern Micronesia...
A mostly dry pattern is currently in place across eastern Micronesia.
The only exception is Pohnpei. A weak trade-wind trough moving
through the state will result in low-end scattered showers and
isolated thunderstorms across the island through tonight. By Tuesday
morning, isolated showers will return to the state. Currently, a
weak Inter-Tropical Convergence Zone (ITCZ) is seen to the east of
the Marshall Islands, with most of the convection east of the Date
Line. Models are adamant that the ITCZ will strengthen and move
across eastern Micronesia through the middle of the week, bringing
increased convection to the region. For now, maintained POPs
(Probability of Precipitation) in the scattered range, that is 30 to
50%. If the ITCZ does develop a bit closer to the forecast points,
POPs could increase a bit more. Late in the week and into the
weekend, the ITCZ looks to fragment again, with a corresponding
decrease in convection across the region.

Combined seas still look to increase over the next few days across
the region. Seas are expected to reach up to 6 feet at Kosrae and
Majuro and up to 7 feet at Pohnpei. Gentle to moderate winds are
expected at Kosrae into the weekend. Gentle to moderate winds look
to become moderate to fresh Friday at Pohnpei and Thursday at Majuro
and continue into the weekend.

Western Micronesia...
The overall weather pattern is evolving as expected, with the Near
Equatorial Trough (NET) continuing to extend across the region
mainly between 3N and 5N from near 155E to beyond 130E and towards
the Philippines. The embedded circulation has shifted westward and is
located near 4N142E, along with the passing trade-wind trough which
is just starting to push into Yap this evening, and will move into
Palau Tuesday. This trough is supporting scattered to numerous
showers and isolated thunderstorms slightly further north than what
models were suggesting, so increased showers from scattered to
numerous at Yap for tonight, and at Palau for Tuesday. Then as the
trough and embedded circulation continue westward, weather at Yap
will dry out fairly quickly starting Tuesday, while the wetter
pattern will slowly decrease through Wednesday at Palau, due to being
closer to the trough axis of the NET. Further east, weather has
dried out for Chuuk Lagoon are areas northward as the Blended Total
Precipitable Water (TPW) satellite product shows drier air with TPW
values around 1.6 to 1.9 inches filtering in from the north, but a
weak zone of convergence north of the NET is producing some spotty
showers to the south of Chuuk Lagoon and near the islands of Losap
and Namoluk, and extending westward towards Polowat, with in an band
of moisture with TPW values around 2.2 to 2.4 inches. The drier air
will continue to filter into Chuuk until about Wednesday night as the
next series of troughs move into the region from eastern Micronesia
as the ITCZ redevelops and then fragments again later in the week.
These troughs will bring scattered showers and isolated thunderstorms
back to Chuuk for the latter half of the week.

Altimetry data shows combined seas of 4 to 6 feet across the region,
with ASCAT showing winds around 10 to 15 kt, with pockets of 20 kt
winds south of 8N and increasing more towards 15 to 20 kt between 8N
and 17N. With convection occasionally producing gusts of 25 kt, and
a trade-wind surge expected to develop east of the Marianas and
mainly north 8N later this week, sustained winds will push up to 20
kt at times, especially around Yap and Chuuk, before decreasing to
back towards 5 to 15 kt this week. the trade-wind surge will also
lead to an increase of the primary trade swell for the latter half of
the week. While surf is expected remain below hazardous levels of 12
feet along east facing reefs, likely peaking at around 8 to 9 feet
Friday and Saturday, swell wrap-around will push surf along north
facing reefs up towards 6 to 8 feet, nearing hazardous levels of 9
feet. Seas will also build in response to the swell, building to 6 to
8 feet Wednesday through Saturday, especially across Chuuk State and
eastern Yap State.

&&

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

$$


Marianas/East and West Micronesia Update: Aydlett
Marianas: Bowsher
East Micronesia: Kleeschulte
West Micronesia: Schank