160
FXPQ50 PGUM 241907
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
507 AM ChST Mon Nov 25 2024

.Marianas Update...
Only slight edits to the forecast this morning. Decreased showers
overnight as the arrival of the trade-wind trough has been delayed
to today. Expect scattered showers through tonight as the trough
passes through the region. With the higher mid to upper-level
moisture and upper-level support look to bring potential for
isolated thunderstorms. Drier air will push into the northern
Marianas, with isolated showers for Tinian and Saipan. However,
lingering moisture and convergence could keep low-end scattered
showers and a few thunderstorms over Guam and Rota. Starting
Wednesday, a surface trough and higher moisture will drift north
through the Marianas and bring an increased potential for showers and
thunderstorms through the end of the work week.

Marine conditions will approach, but look to stay just below Small
Craft Advisory criteria over the coming days. Combined seas of 5 to 8
feet will rise to 7 to 9 feet today and continue through Thursday 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. Winds and seas
look to decrease slightly late week as the trade flow subsides. The
elevated trade swell and longer period northerly swell could keep a
high rip risk for east reefs and a moderate risk for all other reefs
into late week.

&&

.Fire weather...
Guam airport received no rain yesterday and the KBDI rose to 282,
which is still in the low category but is approaching the moderate
category. An increased potential for showers will begin today and
there will be a potential for a wetting rain at times this week,
especially Thursday.

&&

.Eastern Micronesia Update...
Only minor changes were made to the weather forecast. Upped shower
coverage slightly across all three forecast points through tonight,
due to developing showers upstream observed on satellite imagery that
may linger just a little longer. Other than that, the marine forecast
remains unchanged.

&&

.Western Micronesia Update...
An active fragment of an Inter-Tropical Convergence Zone (ITCZ)
upstream is expected to bring higher shower coverage to Yap today and
to Palau through tonight. On-and-off showers continue to be expected
at Chuuk in the short-term. Otherwise, the marine forecast remains
unchanged at all three forecast points.

&&

.Prev discussion... /issued 541 PM ChST Sun Nov 24 2024/

Marianas Synopsis...
Satellite this afternoon shows mostly clear skies and just a few
light, stray showers passing over coastal waters. Moderate showers
pushed along by a weak outflow boundary south-southeast of the
Marianas may pass near Guam later this evening. East of the CNMI, a
broad area of isolated to scattered showers are seen within a weak,
shallow trade-wind trough. Surface observations show moderate to
fresh winds with a few strong gusts, aligning with scatterometry
winds seen just east and west of the islands. Ipan, Ritidian, and
Tanapag buoy data show combined seas of around 5 to 7 feet across the
Marianas, in agreement with nearby altimetry data.

Discussion...
Mostly dry conditions will continue across the Marianas through the
evening. A shallow, westward-moving trade-wind trough will increase
showers in the area beginning late overnight through Monday,
possibly bringing a thunderstorm or two. Trade winds look to see a
slight increase over the next few days as the subtropical ridge
strengthens north of the CNMI. Sustained winds look to stay just
below small craft criteria, but higher gusts in the mid-20s may
become frequent at times, leading to higher, choppier seas which
could become hazardous to small craft this week. Showers will
increase for the latter half of the week, as a surface trough lifts
northwest through the area beginning sometime Wednesday. Recent model
guidance has backed off on how quickly the trough pushes through,
keeping most of the showers south of Guam until Thursday and Friday
as the wave gradually crests the region. Drier conditions look to
resume next weekend into early next week, as trade winds remain
somewhat elevated.

Marine...
Marine conditions will approach but look to stay just below Small
Craft Advisory criteria over the coming days. Combined seas of 5 to 8
feet will gradually rise to 7 to 9 feet through at least Tuesday as
the trade swell increases and longer period northerly swell passes
through. Winds will be moderate to fresh through much of the week,
with strong gusts possible at times.

Eastern Micronesia...
An Inter-Tropical Convergence Zone (ITCZ) extends westward across
eastern Micronesia from the Date Line to Pohnpei. A series of trade-
wind troughs moving across the ITCZ are churning up periods of
scattered showers across the region. This unsettled pattern looks to
continue through the week, with POPs (Probability of Precipitation)
varying from 30% to 50% through the week as the ITCZ meanders north
and south over the next several days.

Marine conditions will remain fairly consistent through most of the
week, Gentle to moderate trade winds are expected to continue through
Friday. Combined seas, though not considered hazardous, will be a bit
choppy through the week. This is due to the combination of a
northeast and north swell and modest wind wave. Seas are expected to
be between 5 and 7 feet through the week, with seas reaching as high
as 8 feet for Majuro on Friday.

Western Micronesia...
Earlier today, a trough passed through Palau and brought some gusty
showers and thunderstorms to the Republic for a couple of hours this
morning, with the airport on Koror reporting a gust around 32 mph
(28 kt) around 0728LST (0828ChST), while an automated station at
Kayangel reported a preliminary gust of 58 mph (50 kt) around the
same time. Gusts quickly dropped off to 23 mph (20 kt) or less after
0900LST (1000ChST), once the trough and cluster of showers and
thunderstorms moved off to the west. Increasing trade convergence
continues to produce scattered showers and isolated thunderstorms
across Palau and eastward, mainly between 4N and 9N, all the way to
Chuuk Lagoon. Yap Proper is still just north of this convergence, so
showers have remained fairly isolated today. The axis of the trade
convergence is expected to lift northward, while trade-wind troughs
within the ITCZ in eastern Micronesia start to move into the region
over the next few days. This will continue to produce periods of
scattered showers and isolated thunderstorms across Chuuk and Palau
through most of the week, while also lifting showers and
thunderstorms into Yap Proper Monday, promoting a wetter pattern at
Yap through most of the week. Sustained winds are expected to remain
around 20 mph over the next couple of days and then start to
decrease slightly to 15 mph as the moderate trade-wind surge weakens.
This will occur as the ridge north of the Marianas moves off to the
east, decreasing the pressure gradient over the region. Higher gusts
will still be possible near heavier showers and thunderstorms, but
there is currently no strong signal for widespread or long durations
of gusty conditions above 30 mph (25 kt) within the models or
current atmospheric environment. The most recent scatterometer data
still shows the overall wind flow across the region at around 15 to
20 kt (17 to 23 mph) over the open ocean.

Moderate to fresh trade winds with some strong gusts will be
possible, especially near heavier showers and thunderstorms. Models
continue to hold steady with sustained winds around 20 kt or less,
which matches current scatterometer data showing winds across the
region at around 15 to 20 kt, so there are no small craft advisories
in effect at this time. Seas are also nearing the expected peak of 5
to 7 feet for Chuuk and Palau coastal waters, while Yap waters are
still expected to peak around 7 to 9 Monday or Tuesday, staying just
below hazardous levels of 10 feet for small craft. After Tuesday
night, models have winds and seas diminishing slightly as the trade-
wind surge weakens.

&&

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

MP...High Rip Current Risk through late Tuesday night for MPZ001>003.

Marianas Waters...None.

&&

$$

Marianas Update: Slagle
Micronesia Update: Montvila