504
FXPQ50 PGUM 160803
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
603 PM ChST Sun Aug 16 2026

.Marianas Synopsis...
Scattered showers and isolated thunderstorms are visible across the
Marianas, and increasing in coverage around Guam and Rota. Gentle
winds are prevailing. Models and observations show combined seas of 4
to 6 feet.

&&

.Discussion...
A convergence zone between the monsoon westerlies and east trade
winds is setting up right over the Marianas tonight as widespread
showers and isolated thunderstorms are now expected over Guam with a
potential for locally heavy rainfall. Precipitation chances will
decrease north of Guam, remaining scattered over Tinian and Saipan.
The convergence zone is expected to move out of the area by tomorrow
morning and be replaced with scattered showers and isolated
thunderstorms. Lower cloud coverage and light winds over Tinian and
Saipan could allow for island effect showers and thunderstorms over
the southern portion of Saipan. Light and variable winds Tuesday
morning will allow for island effect showers and thunderstorms to
develop over Guam, Tinian, and Saipan, likely pushing south as a
north wind begins to move into the area. Depending on the track and
intensity of Invest 92W, another convergence zone may develop Tuesday
night. Afterwards, scattered showers and isolated thunderstorms are
expected most days for the rest of the forecast period. However, a
fair amount of uncertainty remains due to 92W.


&&

.Marine...
Gentle southwesterlies are expected across the Marianas tonight
before decreasing to light to gentle tomorrow, and then light and
variable by Monday. A faster weakening of the monsoon trough to the
west has dropped combined seas slightly to 4 to 6 feet and this is
expected to remain steady before possibly decreasing slightly by
Tuesday. A moderate risk of rip currents continues for the next few
days along south, west, and north-facing reefs. There is a moderate
risk of lightning through the week. A surge of moisture from the
east bring widespread showers and isolated thunderstorms for Guam
coastal waters with shower coverage decreasing to the north and
becoming scattered over Tinian and Saipan. More bands of scattered
showers and isolated thunderstorms will be possible throughout the
week depending on the development and track of Invest 92W in eastern
Micronesia. This system will continue to be monitored closely.

&&

.Tropical Systems...
A developing disturbance, Invest 92W, is centered north-northeast of
Pohnpei near 10N157E. The invest lies within a broad west to east
oriented trough. Latest satellite data shows a weak Low-Level
Circulation Center (LLCC) with some convection near the center. The
strongest convection lies along the trough to the west and within a
band of convergence south of the trough and invest across Chuuk,
Pohnpei and Kosrae States to south of Majuro. Guidance shows the
system moving slowly west-northwest, then turning northwest toward
the far northern CNMI late in the week. There is a large degree of
uncertainty with Invest 92W. However, the general consensus is for
gradual development as 92W moves toward the northern CNMI. The Joint
Typhoon Warning Center (JTWC) has rated Invest 92W as low, meaning
development is unlikely during the next 24 hours. Residents of the
Marianas should continue to monitor forecasts for any changes to the
expected evolution of Invest 92W.

For more information on Invest 92W, see bulletins issued by JTWC
under WMO header ABPW10 PGTW.

Another weak circulation, newly formed Invest 94W, is centered well
north of Yap near 18N136E. Although 94W is currently rated sub-low,
meaning no development is expected over the next few days, model
guidance has shown this region is favorable for development. invest
94W is not expected to affect the Marianas or Micronesia as it moves
easst-northeast to northeast over the next few days.

&&

.Eastern Micronesia...
Invest 92W remains and the associated trough remain active across
eastern Micronesia today. Latest 925mb analysis shows that this
trough is very close to becoming the primary monsoon trough, with
weak troughing now seen from Invest 93W (north of 25N) to Invest 92W.
92W has become a bit more organized, resulting in it being upgraded
from sub-low to low. As the trough strengthens and replaces the
monsoon trough farther north, this will feed more energy into
Invest 92W as it moves northwest, with strong convergence continuing
south of the trough where a southerly push will continue to cross the
Equator and converge with the monsoonal flow. This will maintain an
active pattern across the region for the next several days. Kosrae
and Pohnpei can expect brief periods of little or no showers with
periods of numerous to widespread locally heavy showers and isolated
thunderstorms through the middle of the week. Heavy rainfall capable
of producing flash flooding and mudslides remains a threat for the
next few days. By the end of the week, Kosrae, then Pohnpei, can
expect to see a drier pattern for a couple of days.

For Majuro, the developing monsoon trough will be the main player,
bringing a couple periods of numerous locally heavy showers and
isolated thunderstorms to the Marshalls Monday into Monday night.
Convection will begin to decrease Tuesday, though POPs (Probability
of Precipitation) will remain in the 30 to 50 percent range through
the end of the week.

For the marine forecast, south swell produced by a southern
hemisphere system will continue to produce hazardous surf along
south facing reefs through Tuesday afternoon. Seas will then begin
to subside a bit. For Pohnpei, increasing south to southwest swell
could result in hazardous surf along south facing reefs, though it
appears that surf will remain just below hazardous levels for now.
The Small Craft Advisory for Pohnpei was allowed to expire as winds
and seas have subsided. However, depending on the development of the
monsoon trough and Invest 92W, seas and wind could increase again
around midweek, requiring another Small Craft Advisory. Benign seas
and light to gentle winds will continue for Majuro.

&&

.Western Micronesia...
Satellite observations show partly cloudy skies across Palau and
Yap, and mostly cloudy skies across Chuuk. Altimetry shows combined
seas between 3 and 5 feet across Palau and Yap, and 5 to 7 feet
across Chuuk.

Ridging between the two monsoonal patterns remains in place across
Palau and Yap. The dry monsoonal flow looks to continue through
Tuesday night for Yap and Wednesday night for Palau. Guidance has
begun to converge on a solution that would send Invest 92W north of
the Marianas, allowing for a convergent part of the monsoon pattern
to establish itself over Palau and Yap late this week. Heavy
rainfall and gusty winds will be possible.

Scattered showers are currently present across Chuuk, but shower
coverage is expected to increase to numerous tonight. As Invest 92W
lifts northward, Chuuk will be positioned within the monsoon tail
this week. Widespread locally heavy showers are expected Monday
night through Thursday. Rainfall amounts between 4 and 8 inches will
be possible, which may lead to flash flooding and mudslides. At this
time, Invest 92W looks to remain disorganized until it moves well
north of Micronesia. Gusty winds up to 30 knots will remain possible
near heavier showers.

Winds and seas have fallen below small craft criteria across Chuuk
today, allowing the Small Craft Advisory to expire. Combined seas are
between 5 and 7 feet for Chuuk and will remain choppy through the
week. Seas could become hazardous to small craft towards the end of
the week as the monsoon tail moves over Chuuk. Benign seas of 3 to 5
feet are expected across Yap and Palau through the next several
days.

&&

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

$$

Marianas: Ogle
East Micronesia: Kleeschulte
West Micronesia: Williams