608
FXPQ50 PGUM 011848
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
448 AM ChST Wed Apr 2 2025

.Marianas Update...
Only minor edits to the forecast this morning. The drier trade-wind
pattern continues, with mainly isolated trade showers expected for
the Marianas for most of the week. A trade disturbance looks to
arrive tonight, with a slight uptick in clouds and showers expected
through Thursday morning, especially over Tinian and Saipan where
shower coverage could become scattered.

Nearby buoys and altimetry indicate combined seas have diminished to
5 to 7 feet, and look to remain in that range through most of
tonight. Another pulse of long-period northeast swell will bring seas
back slightly for the end of the workweek. Winds have also
diminished and will generally be gentle to moderate for much of the
forecast period. Winds could become fresh at times with occasional
strong gusts tonight and Thursday over the Tinian and Saipan waters
as a decaying surge in trade winds moves in and bring an uptick in
showers.

A moderate risk of rip currents will continue along west facing
reefs through tonight, then likely becoming high on Thursday as the
trade swell increases. A moderate risk will continue along north
facing reefs. A long period northeast swell looks to arrive late week
and into the weekend and may keep the rip risk high along east
facing reefs.

&&

.Fire Weather...
Only a trace of rain fell at the Guam International Airport
yesterday. This allowed the KBDI to rise, with today`s reading at
630, which is in the high category. Winds will be a bit lower today,
but can be expected to be stronger in higher terrain, and the fire
danger will remain elevated. However, critical (Red Flag) fire
weather conditions look to not be reached. Drier conditions are
expected for the coming days and the fire weather threat will
continue to rise.

&&

.Eastern Micronesia...
Minimal changes were made with this forecast package. Satellite
trends show scattered showers just outside of Pohnpei. Current
thinking is that these showers will build into Pohnpei today.
Otherwise, isolated showers are expected at Kosrae and Majuro.

No changes were to the marine forecast. Seas are expected to
increase through the rest of the week to 6 to 8 feet at Pohnpei and
Kosrae and 8 to 9 feet at Majuro. Seas could briefly exceed 10 feet
at Majuro Thursday night or Friday.

&&

.Western Micronesia...
A few changes were made to Chuuk`s forecast with little to no
changes made to Palau or Yap`s forecast. Satellite observations show
numerous showers just south of Chuuk`s coastal waters. These showers
are expected to move over Chuuk later today, but with lower shower
coverage to start the morning. The forecast included a increase
coverage of scattered showers becoming numerous for Chuuk today.
PoPs were also increased to numerous for tonight as both the GFS and
ECMWF showed continued convection over Chuuk through at least early
Thursday morning.

No changes were made to the marine forecast. Benign marine
conditions are expected today with combined seas increasing through
the second half of the week. Surf could approach hazardous levels for
north-facing reefs of Chuuk late this week.

&&

.Prev discussion... /issued 543 PM ChST Tue Apr 1 2025/

Marianas Synopsis...
Himawari visible satellite shows isolated showers and patchy cloud
cover in the area, mainly over southern Guam coastal waters and just
east of Saipan and Tinian waters. Surface observations and
scatterometry show mostly moderate to fresh trades with frequent
fresh to strong gusts in the area, with slightly higher speeds near
Saipan.

Discussion...
A mild and dry trade-wind pattern continues for the Marianas. There
are patchy showers in the area late this afternoon, which look to
mainly pass over the coastal waters just south of Guam, and between
Rota and Tinian late this evening. CIMMS MIMIC precipitable water
(PWAT) imagery continues to show a fairly dry air mass across the
area with PWAT values generally less than 1.5 inches, and most
showers are anticipated to be light and short-lived tonight. A
passing trade-wind trough may bring a slightly more substantial burst
of showers late Wednesday night through Thursday morning, with
scattered coverage (30 percent chance) expected for Tinian and
Saipan.

Winds have decreased somewhat today, starting off a gradual easing
trend for the next few days, but fire danger remains high for Guam
with dry conditions anticipated to continue. Passing trade-wind troughs
in the latter half of the week could potentially provide a brief
wetting rain, but shower chances remain at only 20 percent for Guam
and Rota through the forecast period. The KBDI (currently in the
high category at 622) is expected to continue to rise. Stronger winds
in higher terrain will yield an especially higher spreading threat
for any fires that start.

Marine/Surf...
Nearby buoys and altimetry indicate combined seas of 6 to 8 feet,
which are expected to fall to the 5 to 7 foot range tomorrow
through Thursday. Winds will diminish slightly, from moderate to
fresh tonight, becoming gentle to moderate for much of the
remaining forecast period. Another pulse of long-period northeast
swell will bring seas back up for the latter half of the week. This
may also bring the risk of rip currents back up into the high
category for east reefs by the end of the week. In the meantime, the
rip current risk will remain moderate for north and east reefs for
the next few days.

Eastern Micronesia...
Increasing convection is seen this afternoon across eastern
Micronesia. This is due to a wide band of trade-wind convergence
that is in place across the region. Along with the convergence, it
is also likely that there are weak, barely discernible troughs
moving through the area, interacting with the convergence to produce
scattered showers and isolated thunderstorms, mainly north of Kosrae
and west of the Marshalls. Pohnpei and Kosrae are seeing scattered
showers this evening and convection looks to increase overnight as
the convergence is enhanced over the area. Maintained isolated
thunderstorms through the night due to the strong instability over
the region. The increased convection will be short-lived at Kosrae,
becoming isolated again by Wednesday morning as the convergence
drifts farther north toward Pohnpei. Pohnpei looks to remain in a
wetter regime through the weekend and into next week as the
convergence remains over the state. For Majuro, a trade-wind trough
currently a little east of the Date Line looks to move into the
Marshalls by Wednesday night, bringing increased convection to the
atoll. This trough will help to enhance convergence across the
Marshalls, maintaining scattered showers there through the end of the
week, with a drier pattern moving back in for the weekend. This
trough and convergence pattern looks to move into Kosrae Thursday
night, then approach Pohnpei by Friday night. Kosrae will then see a
drier trade-wind pattern return early next week, however, this will
be delayed a bit for Pohnpei.

For Pohnpei and Kosrae, moderate to fresh trade winds look to become
gentle to moderate by the end of the week. Moderate to fresh winds
ware expected to remain over the Marshalls through the weekend.
Combined seas of 5 to 7 feet are expected to increase to between 6
and 8 feet at Kosrae and Pohnpei Thursday night due to an increase in
the northeast trade swell produced by a strong mid-latitude low
pressure center east of the Date Line. The increased swell will be
more pronounced at majuro, with seas of 8 to 9 feet expected by
Thursday. Seas could briefly exceed 10 feet Thursday night or Friday.

Western Micronesia...
A developing disturbance near the far southern islands of Palau, has
shifted the band of trade-wind convergence northward. Visible
satellite imagery shows widespread cloudiness and moderate to deep
convection along this feature from EQ to 6N and stretching east-
northeastward across eastern Yap State and Chuuk States. Model
guidance shows poor organization with this pattern, resulting in some
challenges in the timing of scattered to numerous showers. Although,
a wetter pattern is expected in the upcoming days as the convergent
pattern nudges a little farther north. The GFS is keying in on a
period of numerous showers and isolated thunderstorms moving over
Chuuk Lagoon Wednesday, so have included this in the current
forecast, but have leaned more on ensemble models through the
remainder of the forecast period, with high-end scattered showers
expected through Saturday night. Increasing showers are also expected
in the latter half of the week and starting late week for Yap.
Showers have been kept at scattered coverage, but may become numerous
at times for Palau.

Buoy and altimetry data show seas 4 to 6 feet near Palau, 5 to 7
feet near Yap and 6 to 8 feet near Chuuk. A pulse of long-period
northeast swell late this week may slightly add to seas near Chuuk,
but will mainly contribute to an increase in surf heights along north
and east facing reefs. At this time, this is not expected to reach
hazardous levels of 12 feet for east-facing reefs, but may approach
the threshold of 9 feet for north-facing reefs of Chuuk.

&&

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

$$

Marianas: Slagle
East/West Micronesia: Williams