948
FXPQ50 PGUM 250651
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
451 PM ChST Mon Nov 25 2024

.Marianas Synopsis...
Satellite and radar this afternoon show scattered showers and
isolated thunderstorms moving west across Saipan and Tinian coastal
waters. Scatterometry shows east-northeast winds around 16 to 22
knots, and surface observations have shown gusts in the upper 20s at
both Guam and Saipan. Showers are isolated near Guam and Rota with
partly cloudy skies. Ipan, Ritidian, and Tanapag buoy data show
combined seas of around 6 to 8 feet, in agreement with nearby
altimetry data.

&&

.Discussion...
A weak, shallow surface trough is pushing west over the Marianas,
bringing scattered showers and a few thunderstorms over Tinian and
Saipan this afternoon. Showers will taper through the overnight hours,
before the next surface trough begins to nudge into the area from the
south on Tuesday. This will bring higher shower and thunderstorm
chances for Guam and Rota through Tuesday night, while conditions
should remain fairly dry for Tinian and Saipan through Wednesday
night. Come Thursday, a broad area of troughing over western
Micronesia looks to flex north, bringing additional chances for
showers and thunderstorms to the Marianas through the end of the
week. The main concern with any heavy showers will be the potential
for strong gusts, especially as a trade-wind surge continues across
the region. Scatterometry from today and last night reveals moderate
to fresh trades extend across much of the region from 130E to the
Date Line, between roughly 5N and 20N. Trade winds look to increase
slightly over the next day or so near the Marianas, as the
subtropical ridge strengthens north of the CNMI, with wind
potentially sustaining at around 20 knots at times with gusts to
around 30 knots. The ECMWF remains the most aggressive in wind speeds
and in how long winds stay elevated, maintaining the trade surge
through Thursday. Generally, trade winds should begin to relax by the
end of the week as the strong subtropical ridge shifts eastward,
allowing the pressure gradient to relax across the Marianas and
western Micronesia. Surf and rip current risk will remain elevated
for east facing reefs for much of this week given higher trade winds
and swells, with a high risk of rip currents expected to last into
the weekend.

&&

.Marine...
Marine conditions will approach, but look to stay just below Small
Craft Advisory criteria over the coming days. Combined seas of 7 to 9
feet will continue through Friday as the elevated trade swell and
longer period northerly swell pass through the region. Winds will be
moderate to fresh through much of the week as well, with strong gusts
likely at times especially near showers. Elevated winds and trade
swells will maintain choppier, higher seas, which may become
hazardous to small craft at times this week. Winds and seas look to
decrease slightly late week as the trade flow subsides.

&&

.Eastern Micronesia...
A drier pattern than what was previously expected has developed
across eastern Micronesia. The Inter-Tropical Convergence Zone (ITCZ)
that was expected to remain across the region has pretty much
dissipated with only very weak convergence seen mainly north of 8N.
A few weak trade-wind troughs are now the major players across the
area. Troughs are seen near Pohnpei, east of Kosrae and east of
Majuro. These troughs are expected to move slowly westward and
maintain low-end scattered showers and isolated thunderstorms
through the next couple of days across the region, except for
isolated showers tonight at Pohnpei and a short period at Kosrae
Tuesday. Around midweek, models are trying to show the ITCZ re-
establishing across the region along with a trade-wind surge pushing
into Pohnpei and Majuro, remaining north of Kosrae. This will bring
an increase in showers across the region, with POPs Probability of
Precipitation) increasing to around 50% for all three forecast
points. Shower chances then look to decrease over the weekend into
next week as the region becomes a bit more stabilized.

The marine environment looks to become a bit more choppy as we move
through the week. A trade-wind surge will bring increasing winds and
wind waves to the region by midweek. This surge will also be
responsible for a building trade-wind swell. The trade swell, north
swell and wind waves will result in choppy seas Wednesday into the
weekend. Seas could reach as high as 9 feet at Pohnpei and Majuro
for the weekend. Small Craft Advisory conditions are not expected at
this time, however, if the trade swell builds higher than expected,
this could change.

&&

.Western Micronesia...
Trade convergence along with a couple of passing troughs are
producing scattered to numerous showers and isolated thunderstorms
just south of Palau and across the outer islands of Yap and Chuuk
States, while the three main forecast points Palau, Yap Proper and
Chuuk Lagoon are in a lull this evening. As the showers southeast of
Yap Proper and east of Palau continue westward, showers are expected
to become numerous at Palau tonight while occasionally lifting north
into Yap, keeping showers scattered overnight along with the
potential for some isolated thunderstorms. For Chuuk, as this trade
convergence pulls away, the potential for showers will decrease.
However, the troughs left behind by the dissipated ITCZ in eastern
Micronesia will move into Chuuk, and then Yap and Palau, bringing
periods of scattered showers and at times isolated thunderstorms into
the weekend. Sustained winds at Chuuk will start to decrease from 20
mph to 15 mph overnight, while remaining around 20 mph at Palau
through Tuesday, and potentially a little longer at Yap. Higher gusts
will still be possible near heavier showers and thunderstorms, but
there remains no strong signal for widespread or long durations of
gusty conditions above 30 mph (25 kt) within the models or current
atmospheric environment.

Moderate to fresh trade winds will continue at Palau and Yap through
at least Tuesday, with some strong gusts possible, especially near
heavier showers and thunderstorms, creating choppy seas. At Chuuk,
winds have started to decrease slightly and look to be mostly
moderate. Seas look to have peaked at 5 to 7 feet for Chuuk and
Palau coastal waters, while Yap waters are closer to 6 to 8 feet, and
may still hit 9 feet Tuesday. Seas around Palau and Yap are expected
to start to decrease by 1 to 2 feet Wednesday, while Chuuk waters
may start to decrease as early as tonight as winds start to decrease
slightly. However, models are starting to suggest another trade-wind
surge will develop in eastern Micronesia around midweek. This would
start to rebuild the trade swell, affecting Chuuk first later this
week and then Palau and Yap near the weekend. Not expecting
hazardous conditions to develop, but this could keep overall sea
conditions choppy.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through Saturday afternoon for GUZ001.

MP...High Rip Current Risk through Saturday afternoon for MPZ001>003.

Marianas Waters...None.
&&

$$

Marianas: DeCou
Eastern Micronesia: Kleeschulte
Western Micronesia: Schank