913
FXPQ50 PGUM 212057
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
657 AM ChST Fri Nov 22 2024

.Marianas Update...
No meaningful changes were needed for the forecast. Overnight a
fairly quiet night. Only quick moving, short lived isolated cells of
showers could be found in the Marianas waters. There is a weak trough
moving towards the Marianas, however, it may rain itself out before
it gets here. Seas are expected to continue to gradually climb over
the weekend and may build to advisory (10 foot small craft and 9
foot for surf) for levels before falling back down again.

&&

.Eastern Micronesia Update...
No changes were needed to the forecast this morning. Low end
scattered showers are seen at all 3 forecast zones, with a higher
concentration between Majuro and Kosrae, but that is not affecting
the forecast.

Winds of 10 to 20 knots will dominate eastern Micronesia through next
Tuesday. The exception could be Pohnpei Saturday and Saturday night,
where winds could get up to 25 knots, so put in a headline for
possible small craft advisory conditions. It was too early to put out
a full advisory because it`s in the 3rd period. Also, the chance of
small craft advisory winds is only about 20 percent. For waves,
Majuro 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.

&&

.Western Micronesia Update...
No changes were made to the forecast this morning. Low end scattered
showers are seen at Chuuk, moderate at Koror, and isolated showers at
Yap. Overall though, there is good potential for a wet week to build
back in after this brief interlude (at least for Yap).

10 to 15 knot winds will dominate for the most part at Koror and
Chuuk. The exception is Tuesday, where Koror will be 10 to 20 knots
and Chuuk will be 5 to 10 knots. Meanwhile, at Yap, winds will be 10
to 20 knots, so at Yap and Koror, winds will be challenging. In the
Chuuk Waters, seas will be 4 to 6 feet for the period (today through
Tuesday). In the Koror Waters, seas will be 3 to 5 feet, increasing
to between 4 and 6 feet. At Yap, seas will start at 4 to 6 feet and
increase to between 7 and 9 feet. There will be about a 20 percent
chance of a small craft advisory within Yap Waters Monday night
through Tuesday night. Late next week there could be a slightly
higher chance within the Chuuk Waters.

&&

.Prev discussion... /issued 518 PM ChST Thu Nov 21 2024/

Marianas Synopsis...
Just a few clouds and spotty showers are crossing the region, and
these showers are very small in size, typically lasting 5 minutes at
most. Seas have increased into the 6 to 8 foot range, and the water
temperature is 85 degrees at all of the buoys.

Discussion...
The majority of the forecast is quiet, and free of any real forecast
challenges for the forecast, aside from the marine section which does
pose a couple of minor challenges. Overall, look for a dry season-
like pattern to continue with just spotty, light showers crossing the
region. These showers are very small in size and moving at a good
clip (rate of speed), so it may be hard to have even a 5 minute
duration when they pass overhead.

Of course, we`ll see our typical nocturnal influences which could
affect this somewhat, but given abundant dry air above 7000 feet seen
in the time height series and our radiosonde data (weather balloon
data), greatly limiting any growth/intensity potential. This looks to
double (or slightly more) Friday afternoon into the nighttime hours,
as the northern extension of a surface trough passing through Chuuk
gives us a slight moisture boost.

The real "excitement" will be watching model trends, when a building
ITCZ surges northward as it reaches Chuuk and Pohnpei, crossing the
Marianas. The GFS also hints at one or two minor circulations riding
the trough in tandem as they move through. However, both the GFS and
ECMWF ensembles don`t show anything of concern, and the MJO (Madden-
Julian Oscillation) will only be starting to move into sector 5
(which is the Bay of Bengal/Indian Ocean) near Thanksgiving. Thus,
the MJO won`t be in position to give any weak circulation any
"boost". Thus, it looks like while we`ll see increasing rain
potential, it`s nothing too significant and may only last a few days
in terms of increased potential.

Marine...
Seas have increased a foot or so as expected, and they look to hold
in the 6 to 8 foot range through the weekend. The models do show
increasing trades next week, which will help kick-up the wind-driven
waves, allowing seas and surf to increase some, augmented by a
northeasterly and northerly swell. This may allow high surf, high rip
risk, and small craft concerns to develop. However, we still have
plenty of time to observe model trends. Winds will remain in the
gentle to moderate range through Saturday night, becoming moderate to
fresh next week.

Eastern Micronesia...
ASCAT Analysis indicates a weak troughing pattern stretches from
southwest of Pohnpei across northern Kosrae State and eastward over
the Marshall Islands to beyond the Date Line. Satellite images show
that weather conditions are relatively drier today. Models still
indicate a weak ITCZ, along with a westward moving trough arriving
from the east, will trigger patchy showers at times for Pohnpei,
Kosrae and especially for Majuro over this weekend.

A moderate trade-wind flow is gradually developing across the region
and this will cause some increase in winds and waves over the next
few days.

Western Micronesia...
Satellite imagery this evening shows the trough that affected Palau
this morning is now west of 130E and moving towards the Philippines.
There is some weak trade convergence to the south of Yap and just
east of Palau, generate some scattered showers, so expect scattered
showers to move into Palau tonight and lingering into most of the day
Friday, with the greatest potential for some isolated thunderstorms
looking to be Friday. Meanwhile, Yap will remain north of this
convergence, so partly cloudy skies and isolated showers will
continue through Friday night. At Chuuk, satellite shows partly
cloudy skies and isolated showers across most of the state and
extending back towards Pohnpei.

Model streamlines suggest there is a subtle trough just east of
Chuuk, and though polar satellite scatterometer data missed the area,
Himawari visible satellite imagery shows some counter-clockwise
curvature in the movement of the cumulus cloud field between Chuuk
and Pohnpei, suggesting the potential for a subtle trough. However,
there been little vertical growth within the cumulus clouds so far
today, so showers have been spotty east of Chuuk. Since model data
still supports an uptick in showers tonight, supported by the
nocturnal increase in showers that typically happens as the air aloft
cools faster than the ocean and air just above the ocean, decided to
leave scattered showers in the forecast after midnight, but did
remove isolated thunderstorms from tonight`s forecast due to the lack
of upper-level support for deep convection.

As the trough continues westward and increases showers at Palau and
Yap Saturday, models continue to show increasing trade convergence
and moisture extending from eastern Micronesia into Chuuk around
Saturday and then into Palau and Yap around Sunday or Monday. This
pattern will increase the potential for showers and thunderstorms
across the region through the middle of the upcoming week.

Moderate winds will generally prevail for the period, occasionally
becoming fresh at times as wind increase around troughs and trade
convergence and associated showers and thunderstorms. Combined seas
across the region are around 4 to 6 feet, driven by the primary
northeast trade swell. Seas will begin to rise over the weekend as
multiple long-period north swells pass through the region and the
east-northeast trade flow increases. Seas are expected to become 5
to 7 feet around Chuuk by the weekend and by early next week for
Palau. Yap waters could feel more of an impact from the swells, with
seas possibly rising to 7 to 9 feet. Depending and the strength and
how far south the elevated northerly swells penetrate into western
Micronesia, surf could become hazardous, reaching up to 9 feet, and
seas could become hazardous to small craft at around 10 ft. Right now
wave models keep surf and seas just below hazardous levels, but it
will be a trend to watch through the weekend.

&&

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

$$

Marianas: Bowsher
Micronesia: Stanko