883
FXPQ50 PGUM 010746
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
546 PM ChST Fri Aug 1 2025

.Marianas Synopsis...
Satellite and radar imagery is showing increasing clouds and showers
across the Marianas as a surface trough approaches from the east.
Latest altimetry and local buoys are indicating seas of 4 to 5 feet.

&&

.Discussion...
A broad and weak tropical disturbance southeast of Guam within a
large area of surface troughing will continue to slowly push west
across the region through Saturday night. Expect scattered showers
and isolated thunderstorms, with the better coverage expected across
the southern Marianas as the circulation looks to pass near to south
of Guam. The elevated potential for showers and thunderstorms will
continue on Sunday and into next week due to moist, converging south
to southeast flow along the backside of the departing disturbance,
followed by another surface trough and embedded disturbance lifting
northwest out of eastern Micronesia by midweek.

&&

.Marine/Surf...
Light to gentle northeasterlies will turn more southeasterly through
the weekend as a tropical disturbance passes across the southern
Marianas. Winds could become moderate north of the disturbance across
the CNMI. As the disturbance passes through, elevated showers and
thunderstorm chances will persist. Combined seas of 4 to 6 feet,
comprised mainly of a lingering west-northwest swell, will continue
through the weekend, then decrease next week as said swell slowly
subsides. A moderate risk of rip currents will continue along west
and north facing reefs as the elevated west-northwest swell persists.
A strengthening secondary trade swell will likely allow a moderate
risk current risk to develop along east facing reefs by Saturday
night.

&&

.Tropical Systems...
Tropical Storm Iona out in the Central Pacific is expected to cross
the Date Line by Saturday evening as it pushes off to the northwest.
TS Iona looks to pass northeast of Wake Island sometime Monday as a
tropical depression or weak tropical storm, staying well to the
north of the Marshall Islands. A larger swell emanating from TS Iona
could bring higher seas and surf across the Marshalls beginning
Sunday, but likely staying below any hazardous thresholds.

&&

.Eastern Micronesia...
The pattern is looking more interesting today, the persistent
surface trough from the past few days that stretched from north of
Chuuk and east-northeast to west of Bikini Atoll has changed
orientation. It now stretches from a col north-northwest to north of
Pohnpei where it arcs west, then southwest to a circulation southeast
of Guam. Another surface trough extends northeast from the col
through Kosrae to Majuro, where it turns east and intersects the
ITCZ.

Both of these features will continue to foster scattered shower and
isolated thunderstorm development over the next several days as they
move west. A light northwest swell will continue through Saturday
morning, with a southeast light swell also developing as the surface
wind flow veers behind the trough passage. Mainly light to gentle
winds will prevail.

&&

.Western Micronesia...
A somewhat messy ridge-like pattern continues across far western
Micronesia. Satellite this afternoon shows moderate to deep
convection developing over western Yap State, mainly just east to
northeast of Yap Proper, and in an east-to-west band located just
south of Ngulu. For Palau, stratifying island showers are seen just
off the western coastline of Babeldaob and Koror, with scattered
showers and isolated thunderstorms building further south, near and
east of Sonsorol. These showers continue to be supported by very
strong upper-level east-northeast winds increasing divergence aloft.
To the east, numerous showers are stratifying over much of eastern
Yap State and western Chuuk State, with just remnant upper-level
cloud cover over Chuuk Lagoon.

The broad anticyclonic flow over Yap and Palau will gradually shift
north over the next few days, and showers will increase from time to
time this weekend through early next week. As the high pressure
begins to depart, a broad, weak trough and embedded circulation just
southeast of the Marianas will very gradually nudge west into the
area over the next few days, eventually passing to the north of Yap.
For Chuuk, this will make way for a drier ridging pattern for much of
the weekend. The next more robust trough looks to arrive over Chuuk by
Monday, bringing a few more rounds of showers early next week.

Benign marine conditions continue across the region. Recent altimetry
and Babeldaob buoy data indicate combined seas of around 2 to 3 feet
near Palau, 2 to 4 feet for Yap, and 3 to 5 feet near Chuuk. All
three areas continue to see a mixed swell pattern comprised of a
weakening north-northwest swell and the weak background trade swell.
By early next week the north-northwest swell will subside and the
trade swell will be the primary swell across the region.

&&

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

$$

Marianas: Slagle
East Micronesia: Doll
West Micronesia: DeCou