308
FXPQ50 PGUM 181915
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
515 AM ChST Sat Jul 19 2025

.Marianas Update...
Satellite shows cloudy skies over much of the region, from deeper
convection to the south. This is also bringing light, stratiform
rain over Guam and Rota this morning. The main change was to increase
shower and gust potentials today. Convergence in the trade-wind
pattern and the TUTT to the west, are expected to bring scattered
showers, to at times numerous showers, and isolated thunderstorms
today with gusts to 25 mph near heavier showers.

Combined seas of around 5 feet may increase a foot Monday when
another pulse of west-southwest swell reaches the Marianas. If the
swell comes in a bit higher than projected, seas could rise up to 5
to 7 feet next week, possibly increasing the rip risk to west and
south facing reefs as well.

&&

.Eastern Micronesia Update...
Showers are expected to increase slightly more at Pohnpei and Kosrae
today due to a broad trough slowly moving in from the east, bringing
patchy showers to Kosrae this morning and at Pohnpei in the
afternoon. The Intertropical Convergence Zone (ITCZ) remains the
primary trend-setter for much of the forecast period, with a series
of weak troughs expected to traverse the region as said ITCZ
reinvigorates over the coming days. In addition, the marine forecast
remains unchanged as well.

&&

.Western Micronesia Update...
A leading edge of a significant southwesterly monsoon push has been
observed on satellite imagery and the most recent scatterometer
passes overnight, very strong sustained winds, occasional gale-force
gusts and choppy seas that will be hazardous to small craft until
late morning today in Palau Waters. As such, a Small Craft Advisory
has been issued for Palau waters through late this morning. Winds and
seas are then expected to taper down slightly in the afternoon, but
gusts are expected to occasionally be near gale-force in the early
evening hours, before improving steadily thereafter. Other than that,
only a slight decrease in PoPs was introduced to Chuuk through
tonight, but showers are still expected to remain scattered in nature
throughout the day. The marine forecast remains unchanged for all
three locations.

&&

.Prev discussion... /issued 502 PM ChST Fri Jul 18 2025/

Marianas Synopsis...
Satellite imagery shows overcast skies and radar imagery shows
scattered showers and isolated thunderstorms over the Marianas.
Altimetry shows 4 to 5 feet, and both buoys confirm these seas. Winds
are light to gentle.

Discussion...
A trade-wind convergence zone is interacting with the Tropical Upper
Tropospheric Trough (TUTT) and producing showers and thunderstorms
over the Marianas. The convergence zone is expected to pass by over
the next 24 hours or so. Over the next few days, trade-wind troughs
are expected to provide the support to the TUTT that is needed to
keep showers and thunderstorms in the forecast. This support is
anticipated to diminish by Tuesday. Showers are anticipated to clear
up near the middle of next week.

Marine...
Gentle to moderate east winds will continue through the beginning of
next week. Seas are expected to be around the 4 to 6 feet. Surf
along east facing reefs are 5 to 7 feet, and are producing a moderate
risk of rip currents. Surf along all other reefs are below 5 feet
producing a low risk of rip currents. A west-southwest swell may make
its presence known near the beginning of next week. This may cause
the surf to rise enough to produce a moderate risk of rip currents
along south and west facing reefs.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) has weakened and
fragmented across eastern Micronesia. The main players for the region
over the next couple of days will be a couple of trade-wind troughs
traversing the area. The first of these troughs is approaching Kosrae
and should bring increased convection to the island later this
evening. As this trough passes through, it looks to move south of
Pohnpei, leaving only isolated showers there for the next couple of
days. The next trough is seen east of Majuro. This trough is
interacting with a fragment of the decayed ITCZ, bringing scattered
showers and isolated thunderstorms to Majuro tonight. Latest model
guidance shows the ITCZ reinvigorating over the weekend. This will
bring increased convection across the region into next week.

Little change made to the marine forecast. Light to gentle winds are
on tap for Pohnpei and Kosrae through through the middle of next
week. For Majuro, moderate to fresh winds tonight are expected to
become gentle to moderate over the weekend. Combined seas of 5 to 7
feet at Majuro will slowly subside to between 4 and 6 feet early next
week. For Pohnpei and Kosrae, seas of 3 to 4 feet are expected
through the middle of next week.

Western Micronesia...
Expect an active pattern across western Micronesia through the
weekend as the monsoon trough meanders near Palau and Yap. Moist,
converging westerlies and southeasterlies along the trough will
result in scattered to numerous showers and thunderstorms through
Saturday night for Palau and through Sunday night for Yap. Heavy
downpours and gusty winds will be possible with stronger showers and
thunderstorms. Conditions will slowly improve next week as the
monsoon trough is dragged north and west as the tropical disturbance
Invest 96W creeps towards the northern Philippines and Taiwan, with
surface ridging trying to build in its wake.

For Chuuk, a series of surface troughs will pass through the lagoon
through Saturday, with periods scattered showers and isolated
thunderstorms. A surface ridge passing through late weekend will help
suppress shower development. As next week progresses, moist
southerly flow will bring an increasing potential for showers and
thundestorms.

Combined seas of 4 to 6 feet are expected for Palau and Yap,
comprised of a west to southwest monsoon swell and weaker easterly
trade swell. Winds will be gentle to moderate, with fresh to strong
gusts near heavier showers and thunderstorms. Winds will become light
to gentle and seas will lower to 2 to 4 feet next week as the
surface ridge builds in and the monsoon swell subsides. Combined seas
of 2 to 4 feet are expected in Chuuk waters for much of the forecast
period, driven by the primary trade swell. Light to gentle winds
look to lower and become light by later Sunday.

&&

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

$$

Marianas Update: Cruz
East/West Micronesia Update: Montvila
Marianas: Bowsher
East Micronesia: Kleeschulte
West Micronesia: Slagle