555
FXPQ50 PGUM 161955
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
555 AM ChST Tue Jun 17 2025

.Marianas Update...
A few changes were needed to the overnight forecast. The TUTT cell
moved slightly to the north to about 13N140E, which is well west of
Guam. This positioning will help enhance upper-level divergence over
the Marianas. Light winds and daytime heating will make island
enhanced showers and thunderstorms more likely along west coasts of
the islands. An incoming surface trough has moved past 150E, and will
pass overhead later today. Satellite imagery and the radar show a
multitude of quick-moving shower cells over the region and to the
east of our waters. For these reasons, the Probability of
Precipitation (PoPs) was increased to scattered showers for Guam and
Rota for today, and all of the Marianas for tonight.

Altimetry shows combined seas of 2 to 3 feet and both Ritidian and
Ipan buoys confirm these heights. Winds are expected to be light to
gentle. These conditions will allow benign seas to continue. The risk
of rip currents remains low along all reefs and beaches through
Wednesday. The trade swell is expected to strengthen around the
middle of the week. This will bring the east swell up by about a foot
and allow the risk of rip currents to become moderate along east
facing reefs.

&&

.Eastern Micronesia Update...
Little change has been made to Pohnpei and Majuro forecasts, with
low-end scattered showers still expected through tonight. Meanwhile
at Kosrae, the leading edge of a trade-wind surge has moved
sufficiently west. As such, this allows shower coverage to drop
significantly, with only patchy showers expected through tonight.
Other than that, the marine forecast remains unchanged across all
three forecast locations.

&&

.Western Micronesia Update...
A generally unsettled weather pattern remains in store for western
Micronesia. Increased the PoPs a little at Palau, Yap and Chuuk, as
convective activity is expected to persist and remain patchy through
tonight. Meanwhile, the marine forecast remains unchanged for all
three forecast locations.

&&

.Prev discussion... /issued 527 PM ChST Mon Jun 16 2025/

Marianas Synopsis...
Satellite and radar imagery show fair weather across Guam and the
CNMI late this afternoon with isolated showers across the region.
Widespread showers and thunderstorms are found south of Guam closer
to 10N while a TUTT cell is departing the region, now just west of
Guam. Ritidian and Ipan buoys show combined seas between 2 and 4
feet.

Discussion...
A quiet weather pattern across the Marianas will remain in place
through the weekend. The forecasts were updated around midday today
to add a zone of scattered showers and isolated thunderstorms due to
daytime heating over Guam. This led to a few hours of showers and
thunderstorms near Guam`s Orote Point, and the coastal waters to the
west and southwest. A TUTT cell sat nearly overhead of Guam early
this morning providing the extra atmospheric dynamic to produce the
short period of thunderstorms. That TUTT cell is drifting slowly west
and its influence over Guam will likely diminish. Isolated
thunderstorms remain in the forecast for Guam, primarily associated
with island convection potential, but also for peripheral effects of
the TUTT. Otherwise, the forecast for the week ahead is for
prevailing drier, sunnier weather with only isolated showers across
the region. The TUTT will remain in the region for the next 1 to 2
weeks at least, likely slipping northward along 20N and meandering
there.

Marine...
Expect marine conditions to remain benign for the week ahead.
Combined seas of 2 to 3 feet this evening will persist through
Wednesday morning, then build to between 3 and 5 feet by Wednesday
night as trade wind swells build by 1 to 2 feet. There will be a low
risk of rip currents along all reefs and beaches through Tuesday
night, with a moderate risk along east facing reefs by Wednesday.
Seas and surf will subside 1 to 2 feet this weekend.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) remains active across
eastern Micronesia this afternoon. The ITCZ continues to strengthen
and now extends into western Micronesia, though it remains south of
Majuro and Pohnpei. A series of weak trade-wind troughs are seen
across the region as well, that are interacting with the ITCZ in
various locations. As these troughs move through, convection is
expected to flare up along the interaction points, though Kosrae is
expected to see the most activity. There is currently a lull in the
action over Kosrae as one of the troughs is exiting the area,
approaching Pohnpei. However, convection looks to increase as
another trough is approaching Kosrae from the east. The latest CIMMS
MIMIC Precipitable Water (PWAT) product shows increasing PWATs
approaching all three locations, with greatest influx of moisture
seen approaching Kosrae. Therefore, maintained scattered showers and
isolated thunderstorms for Kosrae tonight, with widespread, locally
heavy showers moving in Tuesday morning as the increased moisture
and next trough arrives. The trough now moving west of Kosrae looks
to brush Pohnpei tonight, bringing scattered showers and isolated
thunderstorms to the island for a brief period after midnight.
Farther east, a trough moving into the Marshalls looks to increase
convection at Majuro later tonight as well. The ITCZ is expected to
meander around the area over through the week, bringing periods of
increased convection to all three forecast points.

Other than gusty winds with the showers and thunderstorms, fairly
benign marine conditions are expected through the week and into the
weekend. Combined seas will remain at or below 6 feet for Kosrae and
Pohnpei, at or below 7 feet for Majuro. Gentle to moderate trade
winds will become light to gentle for Pohnpei and Kosrae Tuesday and
around Thursday for Majuro.

Western Micronesia...
A broad disturbance southeast of Yap Proper continues to generate a
fairly unsettled weather pattern over much of Yap State, with
showers beginning to build into the main islands of Palau this
afternoon. South of Chuuk, satellite shows a band of enhanced
convection along the leading edge of the Intertropical Convergence
Zone (ITCZ). Model guidance indicates that the disturbance near Yap
and Palau will gradually open up into a trough overnight, but will
still generate scattered showers and isolated thunderstorms for Yap
through tonight and for Palau through late Tuesday morning. Then, a
period of quieter conditions occurs through Tuesday night or
Wednesday, before a disturbance begins to develop southwest of Palau,
increasing showers through the rest of the week.

For Chuuk, nearby ITCZ activity is expected to keep low-end
scattered showers in the forecast through Tuesday night. The ITCZ
pattern is expected to weaken around Chuuk Wednesday and Wednesday
night, then model guidance shows the ITCZ re-organizing across the
region toward the end of the week as it lifts north over Chuuk,
bringing wetter conditions by 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 days, increasing a
foot or so around Wednesday night or Thursday as trade swell builds
slightly. Palau may experience light southwest swell through Tuesday
night, driven by monsoon-like flow further south. Light to gentle
winds across Palau and Yap increase to light to moderate by Tuesday
night. Meanwhile, gentle to moderate winds across Chuuk, slightly
subside to light to gentle by the weekend.

&&

.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: Cruz