814
FXPQ50 PGUM 201956
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
556 AM ChST Mon Sep 21 2026

.Marianas Update...
Scattered showers will reign across the Marianas today, and through
most or all of the coming week. The current forecast had that well
covered so no changes were needed. There is an interesting
bifurcation near the end of the week though. After reducing waves by
a foot, the ECMWFwave then reduces them further, while the GFSwave
starts whipping them higher again. Tune in tomorrow...

&&

.Tropical Systems...
The new invest area, 91W, is located near 11.9N and 144.1E, or south
of Guam. It is currently rated as having a "sub-low" chance of
becoming a significant tropical cyclone within the next 24 hours,
which means development is not currently expected, but it is being
monitored for when that might start to change.

&&

.Eastern Micronesia Update...
Eastern Micronesia is also being dominated by the monsoon trough.
Based on satellite trends, introduced little change at Pohnpei,
raised PoP`s at Kosrae, and lowered PoP`s at Majuro. Pohnpei has
scattered coverage, much like that in yesterday`s forecast, Kosrae
has showers moving through it, so it was raised to scattered, and
most of the showers are staying south of Majuro, so it was reduced to
isolated.

&&

.Western Micronesia Update...
The weather in Western Micronesia is being dominated by the monsoon
trough, and little change was needed in the forecasts from last
night. Palau will get scattered showers blowing off from the
thunderstorms to their northeast. Yap is likely to be right in the
thick of it, and could have categorical showers much of today and
tonight. Right now they are between two bands, that could change
fairly quickly though. Chuuk has scattered lines of showers moving
through.

&&

.Prev discussion... /issued 552 PM ChST Sun Sep 20 2026/

Marianas Synopsis...
Mostly cloudy skies with isolated showers and light to gentle winds
prevail across the Marianas. Altimetry shows seas of 4 to 6 feet
west of the waters.

Discussion...
Latest satellite and radar data show mostly cloudy skies with
isolated showers across the region. increasing convection is seen
east of the coastal waters and will approach the islands during the
evening, ushering in increased showers and thunderstorms later this
evening, near midnight. Overall, an unsettled pattern looks to
continue across the Marianas through the next several days, with
the islands seeing mostly POPs (Probability of Precipitation) in the
30 to 50 percent range through the week. Tinian and Saipan will see
some brief periods of 20 percent POPs early in the week. Meanwhile,
Guam and Rota will see periods of locally heavy showers Tuesday
into Tuesday night as a weak disturbance drifts by south of Guam.

Marine...
Not much change in the marine forecast. A mix of swells from varying
directions along with small wind waves will make for some choppy
seas, though seas will slowly fall through the week from 4 to 6 feet
down to around 3 to 4 feet later in the week. Winds will remain
mostly light to gentle through the week.

Eastern Micronesia...
A weak, low pressure system is still located north of Kwajalein this
evening with gentle to moderate westerlies across Pohnpei and Kosrae,
becoming light to gentle upon reaching Majuro. Scattered showers and
isolated thunderstorms will be possible at all forecast points
tonight. A dryer trend will begin for Kosrae tomorrow and by Tuesday
night for Pohnpei with only isolated showers expected. Gentle to
moderate west winds will continue into Monday at Pohnpei and Kosrae
with winds easing to light to gentle by Tuesday as the monsoon flow
lifts northward. Southwest to west winds at Majuro may briefly
increase to gentle to moderate tomorrow before dropping back down and
becoming light and variable towards the end of the week. Combined
seas of 4 to 6 feet will continue through early this week at all
forecast points before possibly decreasing.

Western Micronesia...
A special weather statement has been issued for Yap State. Heavy
showers and thunderstorms are expected through the middle of next
week, and gusty winds at times near these heavy showers.

For Palau, scattered showers and isolated thunderstorms will persist
for the next few days. The monsoon pattern that is currently over
Yap State is expected to move in to Palau around Wednesday. Showers
are expected to be scattered through Thursday as the monsoon pattern
moves into the Philippine Sea. Seas are expected to remain 3 to 5
feet with winds light to moderate.

For Yap, there will be widespread locally heavy showers and isolated
thunderstorms. Winds near these heavier showers may be gusty at
times. Models indicate a potential circulation that may develop as
the pattern moves westward. Showers may begin to wane as early as
Wednesday. Rain totals are anticipated to be 1 to 2 inches a day.
Seas are expected to be 5 to 6 feet through Wednesday before
tapering down to 3 to 5 feet for the latter half of the week.

For Chuuk, A surface trough interacting with some mid-level
convergence is producing sporadic scattered showers around the
coastal waters. These showers are anticipated to fill in and bring
rain to the island through Tuesday. Once this trough move westwards,
fairly benign weather conditions are expected to return for the
remainder of the week. Seas are expected to be 4 to 6 feet through
about Wednesday, then drop by a foot for the later half of the week.

&&

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

$$


Marianas/East and West Micronesia and Tropical Update: Stanko
Marianas: Kleeschulte
East Micronesia: Ogle
West Micronesia: Bowsher