426
FXPQ50 PGUM 221916
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
516 AM ChST Sun Feb 23 2025

.Marianas Update...
Small Craft and High Surf Advisories remain in effect, along with a
High Risk of Rip Currents statement. These advisories and statement
remains in effect through at least Monday morning.

The Marianas is anticipated to remain fairly dry for the forecast
period. Winds are expected to be moderate to strong and building up
to near gale force by Tuesday. Fire Danger over the weekend has
diminished due to the the increase cloud cover and the increase of
humidity. The north swell is expected to start falling over the next
24 to 36 hours.

&&

.Eastern Micronesia Update...
The overnight scatterometer pass shows winds have increased as
expected, due to a tightening pressure gradient. This is allowing
wind wave heights to increase, as is a northerly swell. The previous
forecast shift has this well-covered with Small craft Advisories for
all of Eastern Micronesia, and High Surf Advisories for north-facing
reefs at Pohnpei and Kosrae.

Kosrae:
Precipitation-wise, Kosrae stand the best chance to see
scattered showers in the next 24 hours, they`re on the northern edge
of deeper moisture, with PWATs (Precipitable Water Values) generally
in the 2.1-2.2 inch range, which is near normal values, perhaps just
a tad low. The best surface convergence is also co-located within the
northern half of the deeper moisture, generally between 3N and 5N.

Pohnpei/Majuro:
The deeper moisture is "knocking on your doorstep", just to your
south. As such, it looks like isolated showers is all we can hope for
during the next 24 hours. Majuro is a little farther removed with a
"fresh batch" of drier air advecting into the region, with any
showers that pass overhead expected to be brief in nature.

&&

.Western Micronesia Update...
Chuuk:
The main focus was at Chuuk, as your near the southwestern edge of a
trade surge. This shows up nicely in the overnight scatterometer
pass, which shows sustained winds of 15 to 20 knots. Given the tight
pressure gradient, gusts into the 25 to 30 knot range are probable.
Altimetry shows the seas have responded to the increased gradient,
with wind waves and a northerly swell increasing. Seas are averaging
near 8 feet, and they may increase another foot or two in the next 24
hours. For these reasons, the Small Craft and High Surf Advisories
remain in place.

Palau/Yap:
The stronger winds and associated higher waves remain to your north.
That said, increasing winds and seas look possible during early next
week. In the mean time, look for isolated showers to pass overhead
from time to time with gusts of 25 to 30 mph possible, especially at
Yap (due to a higher pressure gradient than Palau) during the next 24
hours.

&&

.Prev discussion... /issued 631 PM ChST Sat Feb 22 2025/

Marianas Synopsis...
Fresh to strong winds with near gale gusts prevail across the region.
Satellite imagery indicates fragments of a shear line moving over
Guam and Rota. Various buoys indicate seas are between 8 and 11 feet.

Discussion...
Lingering fragments of a shear line are expected to bring low-end
scattered showers and mostly cloudy skies to Guam and Rota, with
lesser showers expected at Tinian and Saipan. In addition, winds will
remain to be fresh to strong, with near-gale gusts at times during
the daytime hours across the Marianas. Winds are expected to then
taper down slightly, before picking up significantly once again
around midweek.

Marine...
Combined seas of 8 to 11 feet are expected through late Sunday
night, before tapering down thereafter as the northerly swell begins
to weaken. As such, A Small Craft Advisory remains in effect through
early Monday morning. Even so, A Small Craft Advisory is likely to be
re-issued around midweek, as another major northerly swell and
stronger trade swells make their way across the region. The
aforementioned weakening northerly swell will allow surf conditions
to fall below hazardous levels, and rip current risk to drop to
moderate along north facing reefs by late Sunday night.

Fire weather...
No rainfall was recorded yesterday, allowing the KBDI to rise to
656, which remains in the high category. A moistening trend with
higher relative humidity values and an increased potential for
showers is expected through the weekend, which could result in
reduced fire danger threat. As such, Red Flag Criteria are not likely
to be met, so the Fire Weather Watch no longer remains in effect at
this time. Even so, elevated winds and drier vegetation are still
likely to produce a higher fire threat in the southern portions of
Guam over the next several days.

Eastern Micronesia...
The weather pattern across eastern Micronesia remains fairly
inactive. A couple of trade-wind troughs, one between Kosrae and
Pohnpei, the other between Majuro and Kosrae, are interacting with
very weak trade-wind convergence to bring low-end scattered showers
to Kosrae, with scattered showers expected to spread into Pohnpei
during the evening. These troughs will move out of the region as the
convergence dissipates by Sunday afternoon, resulting in the dry
trade-wind pattern, currently over Majuro, returning to both
locations. Another trough is expected to move through to the south of
Majuro early next week. This trough looks to bring another round of
increased showers to Kosrae and Pohnpei around the middle of next
week. Majuro looks to remain dry through out the period, with only a
few passing showers for the next week.

Increasing pressure gradient due to a transiting mid-latitude high
pressure system will result in mostly moderate to fresh trade winds,
with strong gusts, over the next couple of days. Kosrae is expected
to see a brief period of fresh to strong winds with near-gale gusts
Sunday night. Along with the winds, a building north swell combined
with trade-wind swell and wind waves will result in combined seas
reaching as high as 11 feet for Pohnpei and Kosrae, and 10 feet for
Majuro. These higher seas are expected to reach Pohnpei later this
evening, and should reach Kosrae and Majuro Sunday morning. The north
swell will be high enough to produce hazardous surf along north
facing reefs of both Pohnpei and Kosrae. Later next week, building
trade swell is expected to reach Kosrae, bringing the possibility of
hazardous surf along east facing reefs with it.

One thing of note for Majuro, abnormally high tides are expected to
arrive there around midweek. The increased trade swell combined with
the abnormally high tides could result in inundation of around 1 to
2 feet along north and east facing reefs during high tide. This will
be monitored over the next day or so to determine if any advisories
or headlines are warranted.

Western Micronesia...
Chuuk remains in a dry trade-wind pattern with satellite imagery
showing just a few spotty showers moving through the flow. This dry
pattern is expected to continue through Wednesday, then a trough
moving out of eastern Micronesia will increase showers and the
potential for thunderstorms for the latter half of the upcoming
week. Winds are expected to increase Sunday through Monday as the
pressure gradient increases due to a mid-latitude high pressure
system moving across the Pacific. This will create breezy conditions
while also make seas choppy. Since altimetry shows seas around 10 to
11 feet just north of Chuuk and winds are expected to become 20 to
25 kt by Sunday night, a Small Craft Advisory was issued starting
Sunday morning through Monday afternoon. A floating buoy northwest of
Chuuk also shows a long-period north-northeast swell moving into the
region, and combining with the increasing northeast swell. This will
cause surf to build to around 9 feet along north facing reefs
tonight, so a High Surf Advisory is in effect tonight through Monday
afternoon. By Monday night winds and the north to northeast swell
will decrease allowing seas and surf to drop below hazardous levels.

Palau and Yap are near the shear line that extends south of the
Marianas ends south of Palau. Convergence along the shear line
brought some scattered showers to Palau earlier today but it looks
like most of these showers have pushed off to the west, leaving
isolated showers and mostly cloudy skies. Showers were isolated at
Yap for most of the day but have started to increase during the
afternoon, and are expected to continue through tonight. Models have
the shear line slowly drifting west-northwest through Monday, moving
the potential for scattered showers west-northwest of Palau and Yap
while also allowing winds to relax overnight and through Sunday
night. Then a new shear line will drop into the region as a high
pressure system moves off mainland Asia and increases the pressure
gradient and winds across Yap Monday and Palau Monday night. This
will bring back breezy conditions and the potential for showers.
Satellite altimetry and buoy data from Palau show seas are around 7
to 8 feet this evening around Yap and Palau. Seas may decrease
slightly Sunday, but as winds increase around Monday seas will
rebuild and reach up to 10 feet, along with winds around 25 knots,
creating hazardous conditions to small craft. Also, the north-
northeast swell is expected to build around that time so hazardous
surf along east and especially north facing reefs will be possible
this upcoming week.

&&

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

     High Surf Advisory until 5 AM ChST Monday for GUZ001.

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

     High Surf Advisory until 5 AM ChST Monday for MPZ001>003.

Marianas Waters...Small Craft Advisory until 5 AM ChST Monday for PMZ151>154.

&&

$$

Marianas Update: Bowsher
East/West Micronesia Update: Doll
Marianas: Montvila
East Micronesia: Kleeschulte
West Micronesia: Schank