782
FXPQ50 PGUM 181907
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
507 AM ChST Wed Nov 19 2025

.Marianas Update...
Though the mid and long term trends are unchanged, made a few short
term adjustments for Guam`s forecast to reflect increased early
morning convection. Blended TPW imagery shows a small wave of
moisture that reached Guam late Tuesday evening boosting the drier
evening airmass with a PWAT of 1.3in to 2in around midnight. By
midmorning, thunderstorms in Guam`s coastal waters should diminish
allowing for another day or two of fair weather before the next wave
of moisture arrives by Friday. The increasing moisture Friday-
Saturday will bring about an increase in winds and seas, pushing surf
to around 9 ft along east facing shores which would signal a high
risk of rip currents. Additionally, combined seas could become
hazardous to small craft as early as Friday morning with seas set to
rise to between 7 and 10 ft.

&&

.Eastern Micronesia Update...
Overnight satellite imagery shows that showers and thunderstorms will
be a little slower to arrive than what model guidance currently
shows. Blended TPW shows plentiful moisture stretching across
Pohnpei, Kosrae, and the Marshall Islands - so conditions are ripe
for the eventual production of showers and thunderstorms. The
westward-moving surface trough, now approaching Kosrae, will be that
trigger, more so, the southeasterly flow in its wake, which will
increase trade-wind convergence along the ITCZ axis. Moderate to
fresh trades will persist across the region with areas along 9N and
farther north potentially seeing gusts of 30-35 kt at times. Latest
altimetry data shows seas of 5-7 ft around Pohnpei and Majuro with
4-6 ft seas near Kosrae. Farther north, in the heart of the expanding
trade-wind surge, seas have increased to 7-9 ft. Seas at all 3
locations will increase 1-2 ft by the weekend. 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...
Quiet conditions are seen at all 3 locations early this morning.
Showers and thunderstorms have pushed to the southwest of Palau a
little ahead of schedule, so the early morning forecasts reflects
that improved change. While drier conditions will largely prevail at
Yap and Palau another couple of days, Chuuk will see showers
increasing late this afternoon and into tonight when locally-heavy
showers will be possible as trade-wind convergence increases in the
region. Showers and thunderstorms are still expected to reach Yap and
Palau between Friday and Saturday. Seas of 5 to 6 ft will build over
the next couple of days at Chuuk, approaching 9 ft around Friday.
Seas around Palau and Yap will see a small increase late Thursday or
Friday as north-northwest swell arrives. With the upcoming new
moon phase, high tides will run a little higher so increased surf,
especially across Chuuk, could result in increased shore-side runup
and splashing along windward shores.

&&

.Prev discussion... /issued 600 PM ChST Tue Nov 18 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 7 feet, while buoy data shows
6 to 7 feet sea heights.

Discussion...
A dry trade-wind regime is in full swing for the Marianas. This
regime is expected to change around Thursday night to Friday though.
A trade-wind trough that is currently southwest of Wake Island, will
move into the region. This trough is expected to effect Tinian and
Saipan first, and then Rota and Guam the next day. Scattered showers
and isolated thunderstorms are anticipated for the end of the week.
Pleasant weather is anticipated to return once this trough passes.
Winds through the middle of next week are expected to remain around
15 to 20 mph.

Marine...
Moderate to fresh trade winds are expected throughout the week.
Combined seas of 6 to 7 feet will gradually increase as the trade
swell builds, potentially reaching 8 to near 10 feet by Friday. Seas
and winds could increase further on Friday and into the weekend as a
trade-wind surge builds across the region. This surge may bring
hazardous conditions 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 rip current risk to increase to
high along east facing reefs. There is also a moderate risk of
lightning starting around Thursday night through Saturday night.

Eastern Micronesia...
Convection is on the increase across eastern Micronesia, bringing an
end to the dry pattern that has been over the area for the past few
days. This is due to the Inter-Tropical Convergence Zone (ITCZ)
redeveloping over the region along with trade-wind troughs moving
through. The ITCZ is now seen on the latest ASCAT analysis
stretching west-southwestward the Date Line across Kwajalein, north
of Kosrae to end south of Pohnpei. There is another weak band of
convergence to the south of the ITCZ, that is interacting with a
trade-wind trough to bring scattered showers and isolated
thunderstorms to Majuro this afternoon. Model guidance continues to
show the ITCZ strengthening over the region, though latest runs show
the strength pulsing through the week. Therefore, all three forecast
points should see mostly scattered showers and isolated thunderstorms
with periods of isolated showers. The ITCZ looks like it will be
most persistent over Kosrae, with Pohnpei and Majuro seeing a drier
trend moving in over the weekend.

Gentle to moderate trade winds are expected to continue at Kosrae
through the week, becoming occasionally fresh over the weekend. For
Pohnpei and Majuro, gentle to moderate winds tonight will become
moderate to fresh Wednesday, and remain at this strength through the
weekend. Combined seas of 3 to 4 feet at Kosrae will reach 4 to 6
feet late in the week. Pohnpei and Majuro can expect seas to increase
to between 5 and 7 feet late in the week into the weekend. These
higher seas are due to building trade-wind swell produced by a trade-
wind surge later in the weak as a strengthening high pressure system
moves by to the north of the region, increasing the pressure gradient
across eastern Micronesia.

Western Micronesia...
Satellite this afternoon shows scattered to numerous showers and
isolated thunderstorms focused just west of Palau coastal waters.
These showers are aligned with the axis of a trade-wind trough,
which extends south-southeast into a weak circulation located within
the far western extent of the Near-Equatorial Trough (NET). The
trough near Palau will gradually shift southwest through the next day
or so as the NET moves slightly southward, maintaining scattered
showers there tonight which will diminish through tomorrow.
Elsewhere across the region, showers are mostly isolated, except for
an area of scattered showers which extends along a weak trough over
Chuuk State, to the southeast of Chuuk Lagoon and adjacent waters.
Chuuk will see increasing showers Wednesday with an expected peak
Wednesday night as a remnant ITCZ fragment, currently located near
Kosrae, builds west-northwest through the area. Showers were
increased to numerous (60 percent chance) for Wednesday night with
locally heavy showers possible. This trough will continue onwards
toward Yap Proper, increasing showers there Friday through the
weekend, and to a lesser extent Palau just slightly later on. Chuuk
will continue to see scattered showers through at least Saturday as
a weaker trough or two cross the area.

Altimetry data reveals combined seas around 4 to 6 feet across the
region. Combined seas will remain fairly steady for Palau and Yap
throughout the week, with a slight increase in the latter half of the
week as a pulse of northwest to north swell moves in across far
western Micronesia. Chuuk will see the greatest increase in seas, as
a pulse of elevated long-period north to northeast swell, emanating
from distant strong mid-latitude systems far to the northeast, enters
the area around Friday before diminishing early next week. This will
be monitored closely, as the incoming swell could bring surf up near
hazardous levels of 9 feet along north facing reefs of Chuuk this
weekend. Moderate to fresh winds are expected to continue across the
region for much of the forecast period, diminishing to gentle to
moderate for Palau and Yap by the end of the week.

&&

.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: DeCou