011
FXPQ50 PGUM 021936
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
536 AM ChST Sun Aug 3 2025

.Marianas Update...
Little change has been made to the forecast. Patchy showers and some
thunderstorms will continue to develop across the Marianas as the
disturbance overhead continues to move away to the west, allowing a
ridge to settle in to bring much more pleasant weather Monday. After,
a broad east-west oriented trough emanating from the aforementioned
disturbance will bring back a wetter regime for the first half of the
week. In the meantime, the marine forecast remains unchanged. A
moderate risk of rip currents is expected along west, north, and
east facing reefs of the Marianas for at least the next several days.
As east swell overtakes the west swell by Monday night, rip current
risk is likely to drop to low along west facing reefs.

&&

.Tropical Systems Update...
Tropical Depression Iona crossed the Date Line and entered the
western Pacific late yesterday evening, centered near 18N177E well
east of Wake Island. Iona is expected to weaken as it moves northward
into the sub-tropical ridge and eventually dissipate. The Joint
Typhoon Warning Center (JTWC) and National Weather Service (NWS) in
Tiyan will continue to monitor Iona for any changes in the forecast.

For more information on TD Iona, please refer to bulletins issued by
JTWC under WMO header WTPN33 PGTW and by the NWS under WMO header
WTPQ33 PGUM.

JTWC is monitoring the surface trough across Pohnpei State and the
weak embedded circulation south-southwest of Pohnpei as Invest 94W.
Most model guidance keeps this circulation week, and eventually
opening back up into the trough, so the potential 94W to develop into
a tropical cyclone over the next 24 hours is very low.

&&

.Eastern Micronesia Update...
A broad surface trough extends across Pohnpei State, with a weak
circulation embedded within the trough south-southwest of Pohnpei,
is developing scattered showers and isolated thunderstorms across
the State. JTWC is monitoring this circulation as Invest 94W, but
most model guidance keeps this circulation weak, and eventually
show it opening back up into the trough. A drier pattern extends
across Kosrae and Majuro this morning, with trade convergence
currently north of the two islands, across the northern RMI,
including Kwajalein and nearby atolls. A weak trade-wind trough is
east of Majuro and will be moving through Majuro this afternoon and
then move towards Kosrae tonight, increasing showers slightly.
Otherwise a drier trade-wind pattern is expected for the first half
of the week for the region, with some upticks in showers as weak
trade-wind troughs pass near the islands.

Altimetry and buoy data shows seas are around 3 to 5 feet and seas
are expected to remain fairly benign over the next several days.
Mostly light to gentle winds are expected through the week at Kosrae
and Majuro, with occasional moderate winds possible at Pohnpei today,
mainly associated with showers and thunderstorms.

&&

.Western Micronesia Update...
The weak disturbance west of the Marianas is expected to pass north
of Yap over the next couple of days and is currently generating
scattered showers and isolated showers across the State, mainly north
of 7N. Models show the convection lifting north tonight before
redeveloping over Yap by Tuesday as the main trough axis moves
through. Palau is far enough south that showers are expected to
remain isolated through Monday, before increasing Tuesday and
Wednesday as the aforementioned trough moves through Yap and then
Palau. The broad surface trough and weak circulation, monitored by
JTWC as Invest 94W, is slowly drifting westward and will be producing
scattered showers and isolated thunderstorms across Chuuk State
today and tonight. The circulation associated with 94W is currently
not expected to develop but instead open back up into the trough,
pulling west of Chuuk Monday which should allow a brief period of
drier weather before the next series of weak troughs move through the
region, supporting scattered showers and isolated thunderstorms
around the middle of the week.

Benign sea conditions continue, with little change expected over the
next several days. Altimetry and Babeldaob buoy data continue to
show combined seas of around 2 to 3 feet near Palau, 2 to 4 feet near
Yap, and 3 to 5 feet near Chuuk. The weak north-northwest swell will
continue to recede over the next day or two as the trade swell
becomes more dominant.

&&

.Prev discussion... /issued 310 PM ChST Sat Aug 2 2025/

Marianas Synopsis...
Satellite and radar imagery are showing scattered showers and
isolated thunderstorms across Guam and Rota, with isolated showers
across Tinian and Saipan. Latest altimetry and local buoys are
indicating seas 4 to 5 feet over the waters.

Discussion...
A broad and weak tropical disturbance within a large area of surface
troughing is currently centered just east of Guam. This disturbance
will continue to slowly push west across the Marianas tonight.
Expect scattered showers and isolated thunderstorms, with the better
coverage over the southern Marianas as the circulation center looks
to pass over Guam. The elevated potential for showers and
thunderstorms will continue through Sunday night due to moist,
converging south to southeast flow along the backside of the
departing disturbance. A brief lull in activity is expected on Monday
with a surface ridge and drier air working through the region.
Another round of active weather is expected to return by Tuesday as a
surface trough and embedded disturbance lift northwest out of
eastern Micronesia and towards the Marianas.

Marine...
Light to gentle winds this afternoon will turn more southeasterly
and become gentle to moderate through Sunday as a tropical
disturbance passes across the southern Marianas. Combined seas of 4
to 6 feet, comprised mainly of a lingering west-northwest swell, will
continue through the weekend, to then decrease slowly next week as
said swell 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 bring a moderate rip
current risk along east facing reefs beginning tonight.

Tropical Systems...
Iona, now a Tropical Depression, remains just east of the Date Line
this afternoon and looks like it will cross the Date Line later this
evening. Iona looks to continue to move west-northwest with little
change in intensity over the next couple of days. Iona looks to pass
northeast of Wake Island sometime Monday, staying well to the north
of the Marshall Islands. Swell from TD Iona could bring higher seas
and surf across the Marshalls Sunday, but given the weakening trend
of Iona, models keep seas and surf below hazardous levels.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) extends east-southeastward
across the Date Line, passing just north of Majuro, across
Kwajalein, north of Kosrae and ending at a circulation centered
southeast of Pohnpei and southwest of Kosrae. The circulation and
ITCZ are producing scattered showers and isolated thunderstorms
across Pohnpei and Kosrae this afternoon, with only isolated showers
seen across Majuro as the ITCZ remains north of the atoll. The ITCZ
is expected to slowly drift west while it dissipates over the next
couple of days. For Majuro, a trade-wind trough near the Date Line
will move through the Marshalls, pulling the eastern end of the ITCZ
far enough south to allow increasing convection over the atoll
through Sunday night. By Monday, a dry trade-wind pattern looks to
move in and continue through most of next week. As the ITCZ
dissipates, convection will decrease across Kosrae and Pohnpei, with
the dry trade-wind pattern over Majuro expected to move into the
region Monday. Near the end of next week, a weak trade-wind trough is
expected to move into the region, bringing a slight increase in
convection to Pohnpei and Kosrae.

A benign marine pattern is expected to continue through the end of
next week, with seas of 4 to 5 feet dropping about 1 to 2 feet at
Pohnpei and about 1 foot at Kosrae and Majuro. Seas will then build
about 1 foot around the middle of next week at Majuro. Mostly light
to gentle winds are expected through the coming week at Kosrae and
Majuro, with occasional moderate winds possible at Pohnpei through
Monday.

Western Micronesia...
The broad anticyclonic flow and ridging pattern over far western
Micronesia will gradually shift north of the region through the
weekend. Satellite this afternoon shows just partly cloudy skies and
isolated showers near Yap and Palau, with some island-effect showers
developing over Babeldaob. Similarly, further east, a dry ridging
pattern prevails across Chuuk and much of Yap State, with only
isolated showers seen near Chuuk Lagoon. Northwest of Chuuk, a large,
weak circulation sits near the Marianas with its center just east of
Guam, with showers and thunderstorms building along its southeastern
flank. This system will very gradually nudge west into the region
just north of Yap Proper through early next week as the ridge pulls
further away. This will allow for better shower and thunderstorm
chances for Palau and mainly for Yap, primarily from Sunday through
the middle of next week. For now, although surface forcing is
limited, any convection with sufficient depth will be supported by
strong easterlies aloft.

A weak trough is beginning to push west into Chuuk, with visible
satellite showing a line of showers beginning to increase along its
axis. This will be the first of a series of troughs to move through
the area over the next day or two, maintaining scattered showers and
isolated thunderstorms for the remainder of the weekend and early
next week.

Benign sea conditions continue, and there was very little change to
the marine forecast. Recent altimetry and Babeldaob buoy data
continue to show combined seas of around 2 to 3 feet near Palau, 2 to
4 feet near Yap, and 3 to 5 feet near Chuuk. The weak north-northwest
swell will continue to recede over the next day or two as the trade
swell becomes more dominant.

&&

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

$$

Marianas Update: Montvila
East/West Micronesia Update: Schank
Marianas: Slagle
East Micronesia: Kleeschulte
West Micronesia: DeCou