159
FXPQ50 PGUM 171953
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
553 AM ChST Wed Jun 18 2025

.Marianas Update...
Only a few changes were made to the Marianas forecast, the main
change being the removal of thunderstorms. The radar shows only
isolated showers over the islands and associated coastal waters.
Pleasant weather is anticipated to remain through the beginning of
next week.

The gentle trade-winds will build to moderate overnight and into
Thursday morning. As the trade-winds build, so too will the trade
swell. The swell is expected to build to between 2 and 4 feet, which
will allow the surf to build to between 3 and 5 feet along east
facing reefs, allowing the risk of rip currents to increase to
moderate along said reefs. Winds and seas are expected to diminish
over the weekend.

&&

.Eastern Micronesia Update...
Due to observed increase in convection upstream, upped the showers
for Pohnpei beginning this afternoon, and for Majuro throughout the
day, potentially lasting overnight. These sporadic developments are
also likely to develop a thunderstorm or two as well. Meanwhile,
Kosrae`s weather forecast remains unchanged. Across all three coastal
waters, the marine forecast remains unchanged, with seas expected to
remain in the 4 to 6 foot range before tapering down during the
weekend.

&&

.Western Micronesia Update...
Delayed the showers at Palau to this afternoon, as it looks like
significant convection is not likely in the general vicinity this
morning. A speed divergence zone has situated itself over Yap,
allowing some showers and thunderstorms to develop sporadically
throughout the day, persisting as such through tonight. In addition,
the forecast also remains unchanged at Chuuk, with patchy showers to
taper down in the afternoon. The marine forecast remains unchanged at
all three locations.

&&

.Prev discussion... /issued 439 PM ChST Tue Jun 17 2025/

Marianas Synopsis...
A surface trough is pushing through the Marianas this afternoon with
showers near Guam and Rota, and drier conditions across Tinian and
Saipan. A few thunderstorms were seen on satellite today, primarily
south of Guam. A TUTT cell remains west of Guam, near 140E, with its
peripheral effects waning across the Marianas. Combined seas are
around 2 to 3 feet at the Ipan and Ritidian buoys.

Discussion...
A surface trough pushing through the Marianas today will move west
of the islands overnight, with moisture trailing behind it a little
longer. Shower coverage will taper with a drier end of the week.
Winds the next few days should keep daytime island-heating showers
near Guam to a minimal, or displaced just over the western coastal
waters. The TUTT cell remains in the vicinity west of Guam along
140E, but its peripheral effects are decreasing. Moderate trades the
next few days will subside this weekend. Longer-range models indicate
a bit of a pattern change for next week with lighter winds, more
moisture and a still-active TUTT pattern across the CNMI. While no
large scale features are present in the long range, conditions across
the Marianas could feel more appropriate for the wet season.

Marine...
Marine conditions will remain benign for the remainder of the week,
with only a small increase in seas the next few days. Combined seas
of 2 to 3 feet will build to between 3 and 5 feet by Thursday as the
trade winds and swell increase for the last half of the week. Winds
and seas will subside again this weekend. There will be a moderate
risk of rip currents along east facing reefs Thursday and Friday.

Eastern Micronesia...
Convection has decreased significantly across eastern Micronesia as
the Inter-Tropical Convergence Zone (ITCZ) became fragmented, with
little convergence seen over the forecast points. Latest model
guidance continues the trend of a weakening ITCZ as it slowly drifts
west. There are a few trade-wind troughs moving through the region.
These troughs will bring periodic scattered showers and isolated
thunderstorms to Majuro tonight and to Kosrae tonight and Wednesday.
Otherwise, a fairly dry pattern looks to be in store for eastern
Micronesia through the end of the week. Latest guidance does show
another ITCZ developing across the region over the weekend, bringing
increased showers to all three forecast points. Due to the
uncertainty of the position and strength of this ITCZ, kept
probabilities of showers in the 30% range.

Fairly benign marine conditions will continue through the weekend.
Combined seas of 4 to 6 feet for Kosrae and Pohnpei will subside to
between 3 and 4 feet for the weekend. Seas of 5 to 7 feet for Majuro
will also subside, reaching 4 to 5 feet for the weekend. Gentle to
moderate winds will become light to gentle for Kosrae and Pohnpei
Wednesday night and for Majuro Thursday night.

Western Micronesia...
Benign conditions are expected tonight for Palau, however, scattered
showers and isolated thunderstorm will be possible for Yap as a
trade trough passing to the north may clip the island, with the
Tropical Upper-Tropospheric Trough (TUTT) cell to the north and west
enhances lift across the region. Otherwise, isolated trade showers
expected for Yap in the trough`s wake on Wednesday. Showers and
thunderstorm chances increase beginning Wednesday for Palau and
Wednesday night at Yap as a Near-Equatorial Trough (NET) develops
near to over the main islands of Palau, turning the flow slightly
south and enhancing the moisture, convergence and lift over the
region through the weekend. Showers could become high-end scattered
to numerous and locally heavy for Palau Wednesday night through
Thursday night.

Over towards Chuuk, the Inter-Tropical Convergence Zone (ITCZ) is
becoming fragmented. A weak trade disturbance along the ITCZ could
bring low-end scattered showers through Wednesday morning, with
isolated trade showers then expected through Thursday. Model guidance
shows the ITCZ re-organizing across the region toward the end of the
week as it lifts north over Chuuk, enhancing the convergence and
lift and bringing wetter conditions beginning Thursday night and
continuing through the weekend.

Combined seas of 2 to 4 feet over Yap and Palau waters and 3 to 5
feet near Chuuk will continue for the next couple of days, increasing
a foot or so around Wednesday night or Thursday as trade swell
builds slightly, the lowering 1 to 2 feet towards the weekend as the
swell subsides. Gentle to moderate winds for Yap and moderate winds with
fresh to at times strong gusts for Palau will decrease and become
light to gentle for Palau by Thursday and generally gentle for Yap by
Thursday night as the NET develops creeps north. Meanwhile, gentle
to moderate winds across Chuuk will become light to gentle by the
weekend as the ITCZ creeps north.

&&

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

$$

Marianas Update: Bowsher
East/West Micronesia Update: Montvila
Marianas: Aydlett
East Micronesia: Kleeschulte
West Micronesia: Slagle