754
FXPQ50 PGUM 211903
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
503 AM ChST Sat Feb 22 2025


.Marianas Update...
A Fire Weather Watch, A Small Craft Advisory, A High Surf advisory
and a High Risk of Rip Current statement remain in effect.

No meaningful changes were needed to the forecast. Satellite imagery
shows increased to mostly cloudy skies over the region. Scattered
showers are anticipated for the islands. Altimetry shows combined seas
remaining around 8 to 10 feet. Winds are also expected to remain
fresh with gusts up to near-gale. The Fire Weather Watch maybe
upgraded to a Red Flag Warning if Guam does not get enough of the
showers that are anticipated over the weekend.

&&


.Eastern Micronesia Update...
Pohnpei:
The main change to the forecast was to hoist a High Surf Advisory and
Small Craft Advisory for Pohnpei from 3 PM this afternoon through 3
PM Monday. The combination of a long period (~12 seconds) increasing
north swell, and increasing trade winds, are thanks in part to an
area of high pressure/sub-tropical ridge sliding east (which kicks up
the winds and waves) look like "a solid bet" to occur.

Kosrae and Majuro:
Kosrae will also see increasing winds, seas, and surf for Sunday into
early next week, so advisories are a possibility there with the next
forecast package or two. This is less certain at Majuro though as
the trade surge and pressure gradient may weaken by the time it gets
to you early next week, but it remains a possibility.

&&

.Western Micronesia Update...
The main change to the forecast was to drop the Small Craft Advisory
at Yap. The pressure gradient has weakened enough to allow seas to
subside, which is what altimetry also shows.

Otherwise, no significant changes were made as the previous forecast
remains in line with forecaster thinking with support from analysis
and good model continuity.

&&

.Prev discussion... /issued 516 PM ChST Fri Feb 21 2025/

Marianas Synopsis...
Latest satellite imagery is showing partly cloudy skies and spotty
light showers over Guam and Rota, with mostly cloudy skies and
isolated to low-end scattered showers over Tinian and Saipan.
Local buoys and latest altimetry data are indicating seas of 8 to 10
feet across the coastal waters. Winds are moderate to fresh with
strong gusts.

Discussion...
The weakening boundary that dropped south into Saipan and Tinian
today continues to wash out with showers diminishing. Convergent flow
along a shear line southeast of the Marianas will drift northwest
into Guam and Rota and bring scattered showers late tonight into the
weekend, but likely staying south of Tinian and Saipan. For next
week, mainly isolated showers expected with brief periods of low-end
scattered showers possible with passing trade disturbances. Gusty
winds are expected over the coming days. This, along with the dry
conditions, will result in fire weather concerns and a Fire Weather
Watch is in effect through Sunday afternoon. More information can be
found below in the Fire Weather Section.

Marine/Surf...
Winds and seas are expected to be hazardous to small craft through
the weekend and likely into next week. Fresh winds with strong to
near-gale gusts with a strong subtropical ridge to the north and
multiple shear lines passing through the Marianas. Combined seas will
be 8 to 10 ft as a larger northerly swell, trade swell and wind
waves impact the region. Winds and seas are expected to increase
further early next week.

The north swell has come in a bit larger and a high surf and high
risk of rip currents continues through Saturday night. A moderate
risk of rip currents is also expected for west and east facing reefs.
As the northerly swell subsides on Sunday, the east-northeast trade
swell is expected to increase. The rip risk is expected to become
high for east facing reefs. In addition, the surf and rip risk could
stay high for north facing reefs.

Fire Weather...
A few showers brought 0.02 inches of rain yesterday, which
allowed for the KBDI to rise to 651. Winds will be quite gusty
through the weekend. However, a moistening trend with high relative
humidity values and an increased potential for showers is expected
through the weekend, which could result in reduced fire danger
threat. The Red Flag Warning has been allowed to expire, however, the
Fire Weather Watch is still in effect from this evening through
Sunday afternoon.

Eastern Micronesia...
Eastern Micronesia is now looking a bit drier than previous
forecasts. Latest satellite imagery shows only spotty showers across
the region north of 5N, with low-end scattered showers seen to the
east of Kosrae, south of 5N. A weak trough along with a band of
trade-wind convergence looks to move into Kosrae on Saturday,
bringing low-end scattered showers to the island Saturday and
Saturday night. Otherwise, eastern Micronesia can expect a dry trade-
wind pattern with little rainfall over the next several days.

Meanwhile, changes are in store for the marine environment. Latest
altimetry data, along with the Pohnpei buoy, shows seas of 5 to 6
feet. Farther northwest, high winds behind a strong low pressure
system are generating an increasing long-period northerly swell that
is expected to move into eastern Micronesia over the weekend. Along
with the increasing northerly swell, high pressure moving eastward
from Japan will spread a trade-wind surge across the region. This
will bring fresh winds with strong gusts and an increasing trade
swell to the region. These factors look to combined to bring Small
Craft Advisory level seas and wind to the islands. A Small Craft
Advisory may be issued, starting as early as Saturday night.

Western Micronesia...
Satellite imagery shows showers have remain spotty across Chuuk
State as a dry trade-wind pattern continues to be the main weather
pattern across Chuuk. Over by Yap and Palau, the trade-wind surge
discussed yesterday is not as impressive today as the area of high
pressure producing the pressure gradient and stronger winds is moving
eastward and starting to move further away from Yap and Palau.
Satellite scatterometer data still shows smaller pockets of 20 to 25
kts winds mainly near Yap and north of Palau and along the shear line
fragment east of Yap and just south of the Marianas. Convergence
along the shear line fragment and weakening trade-wind surge is
creating mostly cloudy skies over Yap and Palau, with some scattered
showers starting to move into Palau this evening. There has been some
short-lived thunderstorms recorded by the Global Lightning Detection
(GLD) network well east of Palau and south of Yap, so added a slight
chance of thundestorms to the coastal waters forecast of Palau for
tonight to highlight that there is a slim chance that a thunderstorm
could develop near Palau. As the area of stronger winds continues to
move eastward, winds are expected to decrease slightly at Yap and
Palau through Sunday, while becoming breezy at Chuuk around Sunday.
Due to the limited moisture across the region, a fairly dry trade-
wind pattern is expected to continue across the region through the
weekend and into next week, with showers limited to along the shear
line fragment near the Marianas and any trade-wind troughs moving
through the region. A similar increase in winds near Yap and Palau is
looking more likely for next week as a cold front/shear line drops
south towards the Marianas and winds increase ahead of the frontal
system as another area of high pressure pushes off of mainland Asia.

Altimetry shows seas have increased slightly to around 5 to 6 feet
at Chuuk this evening, while the buoy near Palau is reporting seas
between 7 and 9 feet. Altimetry shows seas are still around 7 to 10
feet at Yap, primarily driven by the pockets of stronger winds around
20 to 25 knots seen around Yap and north of Palau on scatterometer
data, so the Small Craft Advisory (SCA) for Yap remains in effect
through early Saturday morning. As the weakening trade-wind surge
continues eastward, seas will build at Chuuk to around 8 feet later
this weekend, but the highest seas and strongest winds are expected
to be around or north of 10N, so still not expecting hazardous marine
conditions at this time. Winds around Yap and Palau should relax
Saturday and Sunday allowing seas to drop 1 to 2 feet, and allowing
the SCA to end at Yap Saturday morning. Palau`s buoy shows most of
the north to northeast swells are short period (less than 10 seconds)
or a mix of swell and wind waves, so surf will be elevated along
north and east facing reefs, but should remain below high surf
criteria of 12 feet along east reefs and 9 feet along north reefs
through the weekend. A similar pattern to the last couple of days
looks to develop again early next week as a cold front/shear line
drops south towards the Marianas and winds increase ahead of the
frontal system as another area of high pressure pushes off of
mainland Asia. This may cause marine conditions to become hazardous
at Yap and even Palau around Monday or Tuesday as winds increase up
to around 22 knots and seas build back up to around 10 feet. This
could spread to Chuuk later in the week, so continue to monitor the
forecast to see how this pattern evolves.

&&

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

     High Surf Advisory until 5 AM ChST Monday for GUZ001.

     Fire Weather Watch through Sunday afternoon for GUZ001.

MP...High Rip Current Risk through late Sunday night 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: Bowsher
East/West Micronesia: Doll