387
FXPQ50 PGUM 170914
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
714 PM ChST Mon Aug 17 2026

.Marianas Synopsis...
Satellite imagery shows partly cloudy skies and isolated showers
across the region. Latest altimetry indicates combined seas of 4 to 6
ft.

&&

.Discussion...
With Invests 94W to the northwest and 92W to the southeast, the
Marianas are entering a col, meaning gentle westerlies will gradually
ease to light and variable overnight. Due to the buckling of
westerly flow against the easterlies on the western edge of the col,
scattered showers and isolated thunderstorms are forecasted for Guam
and Rota after midnight. There will be a brief lull in shower
activity in the morning for all islands as the col is overhead. Once
the col exits the region to the west, convergence on its eastern
edges could bring increased shower and thunderstorm potential to the
CNMI in the afternoon. Guam, on the other hand, may see island-effect
showers and isolated thunderstorms in the afternoon. Then, bands of
showers are possible due to the surface trough extending from Invest
92W, so shower coverage may remain scattered through midweek. There
is still high uncertainty regarding a potential approach from Invest
92W as it has been quasi-stationary and slow to develop. However,
model guidance should converge on a solution as the week continues,
so Probability of Precipitation (POP) was limited to 40 percent early
next week. This situation will continue to be monitored closely.

&&

.Marine...
A primary westerly swell of 4 ft and secondary north-northeasterly
swell of 3 ft are producing combined seas of 4 to 6 ft, as well as a
moderate risk of rip currents along north- and west-facing reefs
through the week. A long period, elevated northeasterly swell may be
in store early next week should Invest 92W track towards the
Marianas. There is a moderate risk of lightning through the week.

&&

.Tropical Systems...
A largely disorganized tropical disturbance, known as JTWC`s Invest
92W, is currently centered near 9N158E well north of Pohnpei. Most
of the wind field and convection is concentrated in the southern
peripheries of 92W, with recent scatterometer passes and visible
satellite analysis indicating sustained 15-20 kt westerlies carrying
a newly-developing monsoon surge embedded within said wind field
between Chuuk and Pohnpei. This will also allow the system to
further consolidate over the coming days, but not likely to develop
into a significant tropical cyclone over the next 24 hours. As the
system continues to develop, it is expected to begin moving to the
north-northwest around midweek, as a secondary disturbance enhanced
by the aforementioned westerlies builds near Palau and Yap in the
second half of the week. This chain of systems could influence a
large section of the region for an extensive period of time, so do
regularly check the forecasts for more updates as these events
develop over the week. For more information regarding impacts to
Pohnpei and Chuuk, refer to the Special Weather Statement SPSPQ1 for
Pohnpei, and Special Weather Statement SPSPQ2 for Chuuk,
respectively. For more information on Invest 92W, see bulletins
issued by JTWC under WMO header ABPW10 PGTW.

&&

.Eastern Micronesia...
The southwesterly monsoon flow continues across the region, with
Pohnpei seeing over 4 inches on the northwest side of the island, and
additional heavy rainfall continuing at times for Kosrae. Some of the
atolls of the RMI have also seen this, with Mili Atoll showing over
an inch in one hour. A Special Weather Statement remains in effect
for Pohnpei and Kosrae, with Pohnpei looking to have the highest
potential for heavy rainfall and frequent gusts to 30 knots
continuing through the middle of the week. This is due to Invest 92W
continuing to remain weak/slow to develop. This is allowing the
tropical disturbance to linger in the vicinity, with the latest
analyzed position from JTWC (Joint Typhoon Warning Center) having
shifted the position south, with the LLCC (Low-Level Circulation
Center) now centered near 9.2N 157.8E.

The models do show this system lifting off to the north-northwest
towards the weekend. Until then, it looks to remain quasi-stationary
over the coming days. As this occurs, the bulk of the model guidance
shows the west to southwest wind fields increasing in strength over
the next 72 hours, particularly near Pohnpei, as 92W attempts to
become better organized. In the mean time, given satellite trends
and model data, we kept categorical POPs (Probability of
Precipitation) going at Pohnpei and Kosrae for the next 36 hours,
using frequent shower wording, as there will likely be some lulls in
between the heavier rainfall, as the atmosphere temporarily
stratifies (stabilizes) in the low levels. For the latter half of
the week, lingering monsoonal flow along with cross equatorial flow
will keep scattered showers in the forecast for Pohnpei and Kosrae.

Hazardous marine and coastal conditions are ongoing across eastern
Micronesia. For Pohnpei, a Small Craft Advisory was issued this
evening, mainly for frequent gusts tonight and Tuesday, and then
sustained winds and seas Tuesday night through Thursday afternoon. A
High Surf Advisory is in effect along south facing reefs until 3 AM
Thursday for Majuro and 3 AM Friday for Kosrae. This swell is
emanating from two sources in the south Pacific. The first is former
Invest 90P, which continues to produce a cross-equatorial flow from
south of the Equator. The second is from a far more distant low
pressure east of New Zealand and distant high pressure south of
Australia. Marine and coastal conditions will see little improvement
until Invest 92W exits the region and the south swell from the south
Pacific weakens.

&&

.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 continues to keep dry
conditions across Palau and Yap. This dry pattern looks to persist
through Tuesday for Yap and Wednesday night for Palau. Towards the
latter half of the week, a significant flip in the pattern is
expected. The monsoon trough is expected to bridge across the
region, bringing a monsoon surge. Locally heavy rainfall and gusty
winds will be possible towards the end of the week for Palau and Yap.

Scattered showers are currently present across Chuuk, but shower
coverage is expected to increase to widespread tonight. As Invest
92W lifts northwestward, Chuuk will be positioned within the monsoon
tail this week. Widespread locally heavy showers are expected
through Thursday. Additional 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 remain 5 to 7 feet across Chuuk and 3 to 5 feet
across Palau and Yap. Combined seas look to remain benign across
Palau and Yap through Thursday and then look to become choppy on
Friday and going into the weekend. Choppy seas will persist across
Chuuk through the week, making inter-island travel difficult. As the
monsoon surge intensifies south of Invest 92W, winds will increase to
25 kt sustained with gusts to 35 kt late this week across Chuuk.
This will lead to conditions hazardous to small craft by Thursday. A
Small Craft Advisory will likely be needed within the next few
forecast packages.

&&

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

$$

Marianas: Mesa
Tropical: Montvila
East Micronesia: Williams/Mesa
West Micronesia: Williams