666
FXPQ50 PGUM 092008
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
608 AM ChST Wed Dec 10 2025

.Marianas Update...
A shear line is descending into the far northern Marianas, and is now
about down to Agrihan. The shear line will bring some enhanced winds
to Guam and the southern CNMI the next few days as it sinks a little
farther south. As the winds increase, thought about issuing a Small
Craft Advisory, but have held back based on the less than
enthusiastic GEFSwave guidance. The chance of Small Craft Advisory
conditions only reaches 30 or 40 percent, and not until Saturday or
Sunday. Regarding the possibility of shear line weather, the
inherited forecast restricts this to Tinian and Saipan, which is a
good guess for the first shear line of the season, it`s going to hang
up somewhere. With a good forecast in place, no changes were needed
overnight.

&&

.Marine...
Seas are currently 5 to 7 feet. Over the next few days, they are
expected to rise to between 7 and 9 feet within the Marianas Waters.
From the Tinian Waters northward, combined seas could reach 8 to 10
feet, just touching Small Craft Advisory criteria, as mentioned
above. That`s the main forecast problem for the Marianas right now.

&&

.Eastern Micronesia Update...
Near and south of Kosrae, trade winds are converging into the near-
equatorial trough. A trade-wind trough arches northward near Pohnpei.
In the Marshalls, an upper-level low that looks like it wants to be a
TUTT (Tropical Upper Tropospheric Trough) is enhancing the showers,
although coverage remains isolated. This was all covered well in the
inherited forecast so no changes were needed.

&&

.Western Micronesia Update...
The near-equatorial trough lies south of the main forecast points,
however trade-wind troughs will move through Chuuk, Yap and Koror,
bring a mix of isolated and scattered showers. The only possible
issue is timing the showers, which would be difficult at best. The
inherited forecast has a good guess at that in place, so no changes
were needed overnight.

&&

.Prev discussion... /issued 607 PM ChST Tue Dec 9 2025/

Marianas Synopsis...
Gentle to moderate northeasterlies are bringing light showers to
eastern waters of Guam and Rota. Buoys show seas are 6 to 8 feet.

Discussion...
A southward propagating shearline is expected to bring periods of
light rain and windy conditions to Tinian and Saipan Thursday and
Thursday night, with some chance of moving into the weekend if the
shearline takes longer to dip south. Once the shearline situates
itself over the islands, a compact zone of diffusion may form just
200 miles southward of the shearline axis, allowing Guam and Rota to
observe drier, albeit breezier conditions until the weekend.

Marine...
Gentle to moderate easterlies will become moderate to fresh beginning
Wednesday, to then become strong near Tinian and Saipan as a
shearline finally moves in from the north. This may potentially bring
conditions hazardous to small craft in Tinian and Saipan coastal
waters for much of the second half of the week. Combined seas of 6 to
7 feet will slightly increase by a foot or two toward the weekend,
meanwhile 6 to 7 foot seas near Tinian and Saipan may potentially see
at least 10-foot seas during the shearline passage.

Eastern Micronesia...
The main forecast challenge was adjusting downward model POP
(Probability of Precipitation) values based on satellite imagery.
This was mainly done (forecasts adjusted downward) for the next 36
hours (tonight through Wednesday night) at all three locations.
Thereafter, there was still some concern if model forecasted POPs are
too high based on upstream satellite imagery (180 to 160W). We
decided to keep the model forecasts for now during this latter time
period and will re-evaluate during the next 2 forecast packages.

Otherwise, look for mainly gentle to moderate winds to persist at
Kosrae and Majuro. For Pohnpei, light to gentle winds will increase
into the gentle to moderate range by the weekend. Seas will remain in
the 6 to 8 foot range the next few days.

Western Micronesia...
A fairly quiet trade-wind pattern continues. The Near-Equatorial
Trough (NET) looks to have shifted slightly further south of Palau
and Yap, maintaining an area of scattered showers to the south and
east of coastal waters. Yap saw scattered showers briefly today with
drier conditions now just upstream, but showers look to increase
again overnight as a shallow trough shifts west-southwest into the
region, propagating along the northern periphery of the NET. Showers
then look to increase near Palau tomorrow as this feature moves past
Yap Proper and into the area, and the NET axis flexes slightly
northward. This looks to maintain low-end scattered (30 percent
chance) showers near Palau through Thursday night, but models still
keep most of the showers south of coastal waters. Showers will then
remain isolated to scattered across far western Micronesia through
the rest of the forecast period, with the occasional increase owing
to weak, transient features moving through the region along the
northern edge of the NET.

Further east, satellite imagery reveals very dry conditions over and
upstream of Chuuk, with bands of scattered showers seen to the south
of Weno coastal waters, oriented along the NET axis. Chuuk looks to
remain mostly dry through the rest of the week, with models
indicating a wetter pattern beginning to set up on Sunday through
early next week, as a more robust trough moves west into the area
from over Pohnpei and Kosrae.

Buoy data indicates combined seas of 4 to 6 feet across much of the
region, increasing to around 7 feet just north of Yap and Chuuk
waters. The marine forecast remains fairly steady through the week
as the northeast trade swell remains dominant with a gradually
diminishing background north swell. Seas look to increase by a foot
or so this coming weekend with a slight strengthening of the trade
swell. Winds will be light to moderate for Palau and Chuuk
throughout the forecast period, staying mostly moderate for Yap.

&&

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

$$


Marianas/East and West Micronesia Update: Aydlett
Marianas/East and West Micronesia Update: Stanko
Marianas: Montvila
East Micronesia: Doll
West Micronesia: DeCou