153
FXPQ50 PGUM 170731
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
531 PM ChST Thu Jul 17 2025

.Marianas Synopsis...
Satellite and radar imagery show showers building into the eastern
Marianas waters. Altimetry shows combined seas of 4 to 5 feet and the
buoys confirm this.

&&

.Discussion...
A trade-trade wind trough is interacting with the Tropical Upper
Tropospheric Trough (TUTT). This is producing a line of showers and
thunderstorms just outside of the eastern coastal waters. This line
is expected to move westward over tonight and tomorrow. Once this
line passes, passing trade-wind troughs are expected to bring
scattered showers off and on through the rest of the forecast period.
To reflect this, the probability of precipitation (POPs) is
anticipated to be on the line between isolated and scattered
showers or between 20 and 30 percent.

&&

.Marine...
Gentle to moderate east winds will continue through the 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...
A fairly quiet pattern is in place across eastern Micronesia this
afternoon. The main feature across the region is a weakening Inter-
Tropical Convergence Zone (ITCZ) that stretches eastward from south
of Chuuk eastward to end southwest of Majuro. The ITCZ looks to
remain fairly weak through Friday, with transient trade-wind troughs
responsible for anything beyond isolated showers. Currently, one of
the troughs is moving past Pohnpei, resulting in scattered showers
and isolated thunderstorms decreasing to isolated showers during the
evening as the trough exits the area. Latest model guidance does
indicate that another weak trough will brush Pohnpei Friday,
bringing another round of increased convection to the island.
Another trough is expected to move into the Marshalls Friday,
bringing increased convection to Majuro. After this point, a series
of weak troughs will traverse the area as the ITCZ begins to
reinvigorate over the region. This will result in an overall
unsettled pattern across the region.

Light to gentle winds are expected for Pohnpei and Kosrae through the
beginning of next week. For Majuro, gentle to moderate winds will
continue through the beginning of next week. Combined seas of 3 to 5
feet at Pohnpei and Kosrae will slowly subside to between 3 and 4
feet over the weekend. Majuro will see seas of 5 to 7 feet through
the beginning of next week, when seas will drop around 1 to 2 feet.

&&

.Western Micronesia...
Palau remains on the eastern edge of the southwest flow that is
flowing up towards Invest 96W, which is outside of our region. The
heaviest showers remain off to the west, but they continue to
produce outflow boundaries that move across Palau, creating
occasional gust around 25 kt and scattered showers that will continue
through tonight. Yap Proper saw isolated showers today as weak
subsidence aloft, generated by a weak mid-level ridge, helped to
suppress shower development despite low-level convergent southeast
flow. Now that the mid-level ridge has moved northwest of Yap,
scattered showers is starting to develop and should continue through
the night. A broad surface trough, currently over the outer islands
of Yap State, is lifting west-northwest towards Yap and Palau and
will continue to support the development of scattered showers and
isolated thunderstorms across the region through the weekend and
early next week.

Meanwhile at Chuuk, a gentle to moderate trade-wind flow extends
across the State, with trade-wind troughs bringing scattered showers
as they pass through. One such trough is moving through western Chuuk
State, allowing showers to decrease across Chuuk Lagoon this evening.
The next trade-wind trough is exiting Pohnpei and will reach Chuuk
Friday. This overall pattern will continue through the weekend.
Models show a weak ridge developing near Chuuk State early next week
which will make winds light across Chuuk and help to suppress shower
development on Monday.

Combined seas of 4 to 6 feet are expected near Palau and Yap the
next few days, driven by the mixture of southwest monsoonal swell
and the easterly trade swell. Gusty winds from showers and outflow
boundaries may make seas choppy at Palau at times through Saturday.
Seas are expected diminish to between 3 and 5 feet by early next week
as the southwest swell decreases. Combined seas of 3 to 5 feet are
expected in Chuuk waters for much of the forecast period, driven by
the primary trade swell.

&&

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

$$

Marianas: Bowsher
East Micronesia: Kleeschulte
West Micronesia: Schank