692
FXPQ50 PGUM 221803
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
403 AM ChST Sat Nov 23 2024


.Marianas Update Synopsis...
A few convergence driven showers pop up over Rota and Tinian waters
overnight. These showers were fairly short lived. Overall no
meaningful changes were needed to the forecast. The main concerns
for the Marianas is the incoming north swell and trade-wind swell.
These increased swells will bring choppier seas which may build to
advisory levels for both Surf and Small Crafts. Winds are expected to
be moderate to fresh.

&&

.Eastern Micronesia Update...
Only minor edits to the forecast this morning. Did bump up shower
coverage slightly through tonight based off current satellite and
model trend. The ITCZ is expected to be active through the weekend,
with multiple surface troughs traversing through it as well, bringing
scattered to at times numerous showers and isolated thunderstorms
for Pohnpei, Kosrae and Majuro. Gusty winds and heavy downpours
possible near stronger showers and thunderstorms. For next week, the
models are hinting at drier conditions as the ITCZ diminishes, but
multiple trade troughs and trade convergence look to keep an elevated
chance of showers.

Elevated winds and seas will continue through the weekend into next
week. Seas rise to 6 to 9 feet for Pohnpei and Majuro, 5 to 8 feet
for Kosrae, comprised of a higher trade swell and longer period
northerly swells. Winds will be moderate to fresh with some strong
gusts possible, especially near heavier showers and thunderstorms.
Surf will be elevated along east facing reefs of Kosrae, up to 7
feet, but should stay below advisory criteria.

&&

.Western Micronesia Update...
No major changes to the forecast this morning. Scattered showers and
isolated thunderstorms expected for most of the period with elevated
trade flow and multiple trade troughs pass through western
Micronesia. Showers could become numerous at times for Chuuk late
Sunday and Monday as the ITCZ and surface creep north and west over
the lagoon.

Moderate to fresh trade winds with some strong gusts possible,
especially near heavier showers and thunderstorms. Seas will rise
over the weekend as multiple elevated northerly swells pass through
the region and the east-northeast trade flow increases. Seas rise to
5 to 7 feet for Chuuk by late weekend and for Palau by early next
week. Yap waters could feel more impacts from the swells, with seas
possibly rising to 7 to 9 feet early next week.

&&

.Prev discussion... /issued 542 PM ChST Fri Nov 22 2024/

Marianas Synopsis...
Fairly quiet conditions persist across the region with few features
to speak of. Satellite and radar this afternoon show mostly clear
skies over Saipan and Tinian with just isolated showers far upstream.
To the south, widely scattered showers are seen crossing Guam and
Rota coastal waters, moving along the back side of a very subtle,
shallow surface trough. Scatterometry data this morning shows an area
of fresh trade winds over Guam and near Rota, with moderate trades
further north. Guam surface observations reveal a few gusts to around
20 knots (~23 mph). Ipan, Ritidian and Tanapag buoy data show
combined seas of around 5 to 8 feet, which is in agreement with
nearby altimetry data.

Discussion...
Conditions remain quiet across the Marianas this afternoon other
than the increase in showers near Guam and Rota, which is likely a
result of locally-enhanced wind speed convergence. These showers
look to diminish overnight as the area of trade-wind convergence
shifts west of the islands. Trade winds should see a slight increase
tonight, looking to remain steady with moderate to fresh speeds this
weekend. Winds may increase by another few knots Sunday night through
Tuesday night as a trade wind surge builds across the region, due to
a strengthening subtropical ridge to the north. Winds may sustain at
around 20 knots to the low 20s at times, contributing to higher,
choppier seas which may be hazardous to small craft at times early
next week. Showers will also likely see a boost from time to time,
due to locally stronger surface convergence owing to the surge in
trade winds. Overall, conditions remain fairly dry until the middle
of next week, when a sharp surface trough lifts northwest across the
area. This trough looks to break off from a segment of the
Intertropical Convergence Zone (ITCZ) early next week as it extends
westward toward Chuuk. Expect wetter conditions for the latter half
of next week, lasting possibly into the weekend.

Marine...
Altimetry data shows 6 to 8 foot seas well east of the
Marianas and 5 to 7 foot seas to the west, which is in good agreement
with local buoy observations. Seas may increase by another 1 to 2
feet early next week due to an increasing trade swell and
strengthening winds, possibly becoming hazardous to small craft at
times.

Eastern Micronesia...
A surface trough just west of Majuro is producing scattered showers
and isolated thunderstorms across the Marshall Islands from about
Ebon Atoll, up through Majuro, and into Kwajalein and Wotje. Showers
and thunderstorms have been increasing to the southeast of Kosrae as
the trough moves westward and are starting to lift northwest into
Kosrae this evening. At Pohnpei, skies are partly cloudy with
isolated showers, but as the trough continues to drift west, expect
scattered showers and isolated thunderstorms to move into Pohnpei
sometime after midnight, with the best chance of rain looking to be
after sunrise on Saturday through Sunday night. Watching for the
potential for gusty winds this weekend as an upper-level trough is
located just north of the region and is slowly moving eastward. Not
seeing a lot of support for widespread gusty winds as the upper-
level trough is expected to pull away to the northeast Saturday
night, but the GFS is the outlier showing small pockets of 30 mph
gusts developing just north of Majuro Sunday morning and then
progressing westward towards Pohnpei late Sunday night. Gusty winds
are always possible around showers and thunderstorms, but confidence
is not high that such winds will be widespread and it is difficult to
pinpoint exact locations and timing for such localized winds. As the
surface trough continues westward, the GFS and ECMWF show a weak
ITCZ building east of the trough and extending westward as it follows
the westward progression of the trough. This will keep scattered to
at times numerous showers and isolated thunderstorms in the forecast
for Majuro, Kosrae, and Pohnpei through the weekend.

Around Monday or Tuesday, the GFS and ECMWF show the southeast flow
associated with the ITCZ diminishing, decreasing convergence and the
overall potential for showers and thunderstorms across the region.
The GFS is currently trending slightly drier through Wednesday while
ECMWF depicts a trade-wind trough crossing the Date Line around
Tuesday, followed by increased trade-wind convergence across the
region. The GFS eventually shows increasing trade-wind convergence
across the region but this is delayed until Thursday.

Winds of 10 to 20 knots will continue eastern Micronesia through
at least the middle of the upcoming week. The previous forecast
mentioned the potential for 25 kt winds at around Pohnpei Saturday
and Saturday night, but the potential was around 20 percent. This
potential has not changed much within the GEFS wave guidance, so
while gusts to 25 kt are included to note gusts near showers, winds
are expected to remain around or below 20 kt through the weekend. For
waves, Majuro Coastal Waters will start at 5 to 7 feet and increase
to between 7 and 9 feet. Kosrae will start at 4 to 6 feet and
increase to between 6 and 8 feet. Pohnpei will start at 4 to 6 feet
and increase to between 7 and 9 feet Saturday, then start to
gradually diminish as the primary northeast and secondary north swell
slowly decrease.

Western Micronesia...
Satellite shows fair weather over Chuuk and Yap today while patchy
showers were moving across The Republic of Palau, mostly just south
of Koror. ASCAT Analysis indicates a weak surface trough causing the
showers over Palau, and light to occasionally moderate trade winds
were seen over most of Western Micronesia. Models indicate patchy
showers will eventually arrive from the east, moving to near Chuuk
by late in the weekend, and toward Yap and perhaps Koror as next week
progresses.

Moderate to fresh trade-wind flow is gradually developing across
Micronesia, especially northern parts of Micronesia, and this will
cause some increase in winds and waves over the next few days. Marine
conditions may become choppy at times for Chuuk and Yap by next week.

&&

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

$$

Marianas: Bowsher
Micronesia: Slagle