281
FXPQ50 PGUM 031938
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
538 AM ChST Fri Jul 4 2025

.Marianas Update...
Satellite and radar observations show partly cloudy skies and
isolated showers across the Marianas. Ritidian and Ipan buoys show
combined seas between 2 and 4 feet.

Overall, only minor edits were made with this update. The main
change was to scale back showers for tonight to isolated across the
zones and most of the coastal waters. Scattered showers and isolated
thunderstorms will be possible across the northern coastal waters of
Saipan and the southern coastal waters of Guam. Both the GFS and
ECMWF have delayed the onset of showers for the islands until
Saturday with perhaps Sunday and Monday being fairly wet. This is
reflected in the Time Heights where the better deep layer moisture
starts to arrive Saturday night.

No changes were made to the marine forecast with this package.
Combine seas of 2 to 4 feet look to continue through the weekend
before increasing a foot or so as a southwesterly swell potentially
moves into the region.

&&

.Eastern Micronesia Update...
A trade-wind trough is approaching Majuro and will bring scattered
showers and isolated thunderstorms this afternoon. This forecast is
bringing the showers in a little earlier. A second trade-wind trough
is generating scattered showers with little or no thunderstorm
activity near and north of Kosrae and near and east of Pohnpei.
Little change was made at Kosrae, where wet today and drying out
tonight looked good. Also little change at Pohnpei, where wet both
today and tonight also looked good.

Seas are 4 to 6 feet at Majuro and 3 to 5 feet at Pohnpei and Kosrae.
This difference is largely due to stronger trades near Majuro,
getting weaker as you move westward. 10 to 15 knots at Majuro becomes
5 to 10 knots at Pohnpei and Kosrae.

&&

.Western Micronesia Update...
Chuuk has weak ridging moving in between two trade-wind troughs.
Therefore reduced the showers and eliminated the thunderstorms today.
Made little change tonight as the weather near Pohnpei could be
moving in by then. Not much change at Yap where they`re mainly
getting high clouds blowing off the convection to the south.
Convection has filled in some near Palau, so retained the scattered
wording, but raised the PoP`s by 10 percent both today and tonight.

Winds are 5 to 10 knots throughout Eastern Micronesia, at Chuuk they
are trades from the east and southeast. In Yap and Palau, they are
monsoon winds from the south, southwest and west. In the area between
the convergence is producing a great many showers and thunderstorms,
and possibly a weak circulation is beginning to spin up. It would be
a few days before it presented any problems, if even then. Seas at
Chuuk are 3 to 5 feet, similar to Pohnpei. Seas at both Yap and Palau
are 2 to 3 feet.

&&

.Prev discussion... /issued 552 PM ChST Thu Jul 3 2025/

Marianas Synopsis...
Gentle southerlies prevail, with satellite imagery and Doppler radar
indicating a few shallow cells on the outskirts of Guam and Rota
waters. The buoys indicate seas are around 3 feet.

Discussion...
A ridge has formed on the lee side of the monsoon trough shifting
northward, allowing a drier regime to return to the Marianas
overnight. Afterwards, showers and thunderstorms will begin to return
to the region as Tropical Storm Mun (formerly Tropical Depression
04W) southeast of Japan, continues to induce a strong monsoon pattern
across much of Micronesia immediately west of the Marianas. This, in
turn, will produce an unsettled weather pattern over the islands this
weekend.

Marine...
Combined seas of 3 to 4 feet are expected through much of the
weekend, before picking up another foot early next week. A moderate
risk of rip currents is expected along east facing reefs of the
Marianas for much of the week, with potential for the risk to become
moderate along west facing reefs once a secondary westerly swell
arrives in the first half of next week.

Eastern Micronesia...
There are a few major features across eastern Micronesia. The first
feature is near the Date Line, a trade-wind trough. This feature is
bringing scattered showers and isolated showers. The trough is
expected to make its way to Majuro in the next day or two.

The second feature is the persistent trade-wind trough that extends
from northern RMI south to Kosrae. This one is most convectively
active in the northern RMI, over Kwajalein, Wotje, Utirik, Ujae and
Rongelap islands and atolls. These showers are further being enhanced
by upper-level divergence associated with the Tropical Upper
Tropospheric Trough (TUTT). The showers near Kosrae are being
enhanced by increased convergence along the southern portion of the
trade-wind trough. This feature will gradually move westwards over
the coming days. Behind this on the time scale of 3 to 5 days out,
the trade-wind trough currently located near the Date Line is
anticipated to arrive at Kosrae.

The third area of interest is over Pohnpei. Surface level convergence
of both speed and direction is producing isolated to scattered
showers in the area. This will make way for the troughs mentioned
above, which look to arrive over the weekend and later next week
respectively.

Altimetry shows combined seas of 4 to 6 feet over the region. Winds
are expected to be light to moderate overall, with stronger winds
near heavier showers. Seas are expected to remain benign over the
forecast period.

Western Micronesia...
A mostly gentle westerly monsoon flow persists across Palau this
evening, with occasional moderate to fresh gusts from nearby showers.
Himawari visible satellite shows isolated to scattered showers
developing in the area, mainly to the west of Koror and near
Sonsorol, with patchy high-altitude cloud debris seen over much of
the region. To the east, a surface ridge is seen over Yap State,
currently located near Sorol and slowly shifting west toward Yap
Proper. Only isolated showers and partly cloudy skies are seen near
Yap Proper this evening, but showers are expected to increase
overnight. Model guidance points to increasing convergence within the
monsoon flow over far western Micronesia leading to a build-up of
showers overnight, mainly just west of Yap Proper over the Republic
of Palau. The increase from isolated to scattered showers was kept in
Yap`s forecast for tonight, and Palau`s Probability of Precipitation
(PoP) increases from 30 percent this evening to 50 percent after
midnight. A mostly gentle monsoon flow will persist into next week
across the region, but Palau and Yap can expect a relatively drier
weekend as a weak ridging pattern sets up across the area.

Chuuk can expect a mostly gentle trade flow through the weekend with
periods of scattered showers, associated with convergence along the
westernmost periphery of the ITCZ. Chuuk Lagoon currently sits along
a convergence boundary just east of a weak disturbance located over
Eauripik in Yap State, with scattered showers just to the south of
Weno. Quieter conditions are expected around Sunday as the ITCZ
retreats further east of the area.

Overall benign marine conditions continue. Despite mostly gentle
winds in the forecast, some fresh gusts will possible near heavier
showers and thunderstorms through the weekend. Combined seas of 3 to
5 feet across the region will come down a foot or so through the
weekend with swells and wind waves relaxing slightly.

&&

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

$$

Marianas: Williams
East/West Micronesia: Stanko