038
FXPQ50 PGUM 061832
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
432 AM ChST Mon Jul 7 2025

.Marianas Update...
A lull in surface winds, speed divergence aloft, and ample
atmospheric moisture, is allowing continuously training showers and
thunderstorms to sit just off the coast of the Mariana Islands into
early this morning. As such, this localized instability is expected
to produce sporadic heavy showers and thunderstorms primarily over
Guam and potentially Saipan the rest of today. If showers and
associated clouds clear out later in the morning, island convection
under extensive island heating may develop in the late afternoon
hours. In the long-term, shower potentials continue to remain
elevated throughout the week, as moist, convergent southerlies
develop. The marine and surf forecasts remain unchanged.

&&

.Eastern Micronesia Update...
A broad trough at the leading edge of the Intertropical Convergence
Zone (ITCZ) is generating a large area of unsettled weather across
the Marshalls and parts of Kosrae State this morning. Satellite and
scatterometry data also indicate another area of convergence across
Pohnpei, although the bulk of convection is to the northwest. Saw
support to slightly increase PoPs to 50 percent for Majuro and 40
percent for Pohnpei today based on latest satellite and model trends.
Otherwise, the rest of the forecast remains unchanged. Latest
observations show gentle to moderate winds and seas 3 to 5 feet
across the region.

&&

.Western Micronesia Update...
Overall, no major changes were made to the forecast. A disturbance
over eastern Yap State remains poorly organized, resulting in
showers and cloud cover decreasing over Chuuk Lagoon overnight.
Meanwhile, convergent west-southwesterlies focus convection
northwest of Yap, with only spotty showers over the main islands of
Yap and Palau this morning. Model guidance is picking up on a brief
increase in showers near Palau. Seeing some support on satellite
where an area of scattered showers is seen west of Palau waters.
Reflected this trend in the forecast, with morning scattered showers
decreasing back to isolated by the afternoon.

Scatterometry shows light west-southwesterlies across the main
islands of Yap and Palau, with light and variable winds over Chuuk.
However, this is expected to become more of a light to gentle
southeasterly flow today. Buoy and altimetry show 1 to 3 foot seas
over Palau and Yap, and 3 to 4 feet near Chuuk.

&&

.Prev discussion... /issued 458 PM ChST Sun Jul 6 2025/

Marianas Synopsis...
Satellite and radar imagery are showing mostly cloudy skies with
isolated to low-end scattered showers, mainly over the coastal
waters. Locally buoys are indicating seas around 3 feet.

Discussion...
A 500mb level vorticity maximum sliding down along the eastern edge
of an upper-level high is centered to the west of the islands. This
disturbance, in and of itself enough to bring showers, also prevented
sufficient daytime heating and destabilization for heavy island-
effect showers and thunderstorms to fire off, due to the abundant
mid to high level cloudiness. Any breaks in the clouds have resulted
in some heavier showers developing, with one currently west of Apra
Harbor. Keep scattered showers (Probability of Precipitation (PoPs)
40 percent) through tomorrow as the upper-level disturbance slowly
dives south and a surface trough slides through late tonight into
tomorrow. If enough clearing tomorrow, could see island-effect
showers and thunderstorms firing off as well as winds will be light
to gentle from the southwest. Shower potential will remain elevated
throughout the week (30-40 percent PoPs) as moist, convergent
southerly flow develops.

Marine/Surf...
Light and variable winds this evening will become light to gentle
from the southwest after midnight. Winds will slowly pick up early
next week as the high pressure ridge shifts east and the southerly
flow increases, with winds becoming gentle to moderate on Tuesday,
then decreasing slightly beginning Wednesday. Combined seas of around
3 feet are expected for most of the week, possibly increasing late
week or the weekend as a west-northwest swell emanating from a
distant tropical disturbance to our northwest arrives.

A low risk of rip currents is expected along all reefs for most of
the week. Surf and rip risk could rise late week or next weekend
along north and especially west facing reefs as aforementioned west-
northwest swell arrives

Eastern Micronesia...
Not much has changed from yesterday in the model forecasts or
forecaster thinking. An unsettled pattern continues this afternoon
with a weak circulation south of Chuuk, and an attendant surface
trough stretching northeast through Pohnpei from it. Then we have a
col centered over the western coastal waters of Kosrae, with one
trough departing majuro to the west and another trough located
southeast of Majuro.

These features will help to focus convection over the next several
days, as additional disturbances in the trades are seen approaching
from east of the Date Line. MIMIC water vapor imagery also shows
PWATs (Precipitable Water Values) generally in the 2.4 to 2.9 inch
range, providing ample moisture for convective development, with the
troughs (disturbances) helping to focus any shower and thunderstorm
coverage and intensity. As such, scattered showers and isolated
thunderstorms will be common most of the week. East to occasionally
southeast winds, albeit light, will allow seas to build slightly due
to better fetch length/direction.

Western Micronesia...
Western Micronesia has a complicated wind flow pattern as the monsoon
westerlies interact with the northeast trades. As easterlies have
nosed in near and east of the Philippines now, it may no longer be
proper to call these monsoon westerlies, as their connection to the
Indian subcontinent has been severed. Although most of the winds are
light to gentle, there is still a fair amount of convergence,
especially where easterlies and westerlies directly run into each
other. This is mainly north of Yap though, so the forecast for the
islands themselves is fairly laid back, consisting mainly of
scattered showers, starting Tuesday night at Chuuk, and on Tuesday
at Yap and Koror, Palau. There will be periods of thunderstorms mixed
in though as pockets of convergence flare up.

For the marine forecasts, winds will be light to gentle, except
possibly for gusts near showers and/or thunderstorms. Seas will be 3
to 4 feet at Chuuk and 2 to 3 feet at Yap through Wednesday, then 3
to 4 feet, and 2 to 3 feet at Palau through Tuesday night, then 3 to
4 feet. The only real weather related threat to mariners this week is
lightning, so be ready to head below deck if any starts to occur in
your area.

&&

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

$$

Marianas Update: Montvila
East/West Micronesia Update: Cruz
Marianas: Slagle
East Micronesia: Doll
West Micronesia: Stanko