940
FXPQ50 PGUM 140830
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
630 PM ChST Mon Sep 14 2026

.Marianas Synopsis...
Visible satellite imagery depicts mostly cloudy skies and scattered
showers. Altimetry indicates combined seas of 3 to 5 ft.

&&

.Discussion...
A surge in moisture has moved over the region which can be attributed
to Invest 90W, the monsoon trough, and a surface trough. Model
guidance indicates showers to continue over the region with a heavier
concentration over Saipan and Tinian tonight and Tuesday, so the
forecast zones were split to account for this spatial and slight
coverage difference from Rota and Guam. Then, depending on Invest
90W`s evolution (discussed in the Tropical Systems section below), a
dry spell may occur over the region should 90W track northwest
toward the northern CNMI. The monsoon trough will follow, bringing
increasing showers and winds possibly this weekend.

&&

.Marine...
Combined seas of 3 to 5 ft will slowly build, possibly peaking up to
7 ft around the latter half of the week. There is a moderate risk of
rip currents along north- and east-facing reefs at least through
Tuesday night. The primary northeast trade swell will persist,
potentially building by a foot for Saipan and Tinian should 90W pass
through the northern CNMI. This will also increase the period of said
swell, so surf along north- and east-facing reefs may build as well.
Then, a secondary southeast swell will reach the region due to the
monsoonal inflow into 90W. This swell may eventually build and shift
to the southwest by the end of the week should the monsoon trough
shift north over the region.

&&

.Tropical Systems...
A developing disturbance, Invest 90W, is centered east of Guam along
the monsoon trough near 13N154E. Invest 90W is currently moving
slowly northwest and has become a bit more organized over the last
24 hours. 90W is now rated medium due to favorable conditions for
development. Medium indicates that development is likely, but not
within the next 24 hours. It is still difficult to identify a good
Low-Level Circulation Center (LLCC), however, satellite shows that a
weak, poorly defined circulation has slowly consolidated over the
past 12 hours. Both deterministic and ensemble model guidance agree
with a slow development over the next 1 to 2 days as it tracks
northwest toward the northern CNMI. Invest 90W will be monitored
closely over the next few days.

For more information on Invest 90W, see bulletins issued by the
Joint Typhoon Warning Center under WMO header ABPW10 PGTW.

&&

.Eastern Micronesia...
A very dry pattern is now in place across eastern Micronesia as
Invest 90W moves more northwest, slowly pulling the monsoon trough
along with it. This dry pattern looks to continue for the next
several days for Pohnpei and Kosrae, with only a brief increase in
POPs (Probability of Precipitation) to around 30 percent on
Thursday, with the dry pattern returning Friday into the weekend.
For Majuro, there will be periods of increased showers as the
monsoon trough continues to affect the Marshalls, with weak
transient circulations passing through and enhancing convection at
times.

For the marine forecast, not much of a change. Seas are expected to
remain between 3 and 5 feet across eastern Micronesia, with mostly
light to gentle winds expected through the week at Pohnpei and
Majuro, and occasional moderate winds midweek at Kosrae.

&&

.Western Micronesia...
Weather in Western Micronesia this week will continue to be dominated
by the monsoon trough. Koror Palau will be getting some much needed
rainfall with scattered showers expected through Wednesday. The
showers will then thin a bit for the rest of the forecast period,
which extends through Saturday. Winds will be from the west or
southwest at 10 to 20 knots for the entire period. Seas will be 5 to
7 feet tonight, then gradually diminish to between 3 and 5 feet by
Saturday. This will make for marine conditions that could be
challenging tonight and Wednesday through Friday, but are expected to
stay just below Small Craft Advisory criteria.

Yap will have scattered showers for the rest of this week, with the
possible exception of Wednesday night, when the showers could
increase to numerous. Winds will be from the west at 5 to 15 knots
most of the period, however they could increase from Wednesday night
through Friday and reach 10 to 20 knots. Seas will be 5 to 7 feet
through Thursday, then build a foot Friday to between 6 and 8 feet,
then diminish back to between 5 and 7 feet Saturday. This will result
in challenging marine conditions Wednesday night through Friday,
while they will be benign through Wednesday and on Saturday.

Chuuk will have southwest winds of 15 to 25 knots through Tuesday,
which makes marine conditions hazardous and has required a Small
Craft Advisory through Tuesday. Also, southeast to southwest swells
of 5 to 7 feet are requiring a High Surf Advisory through Tuesday,
which may need to be extended further, possibly through Wednesday.
Chuuk will have scattered showers tonight and Tuesday night, with
isolated on Tuesday. Isolated showers will then dominate Wednesday
through Friday, then weather could moisten again Saturday. After
Tuesday, winds will be 10 to 15 knots from the southwest, with gusts
to 25 knots possible Tuesday night. Seas of 6 to 8 feet tonight could
build to between 7 and 9 feet Tuesday, then diminish to between 6 and
8 feet again Tuesday night. They could diminish further to between 5
and 7 feet Wednesday night and 4 to 6 feet on Thursday, then remain
at that level through Saturday. This would result in marine
conditions that are hazardous through at least Tuesday, challenging
on Tuesday night and perhaps Wednesday, then becoming benign
Wednesday night.

&&

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

$$

Marianas: Mesa
East Micronesia/Tropical Systems: Kleeschulte
West Micronesia: Stanko