771
FXPQ50 PGUM 100814
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
614 PM ChST Wed Sep 10 2025

.Marianas Synopsis...
Satellite imagery shows partly cloudy skies, radar shows isolated
showers. Buoys show 3 to 4 feet sea heights. Overall, pleasant
weather is expected.

&&

.Discussion...
Fairly pleasant weather is in store for the Marianas. The main
concern through the beginning of next week are isolated showers
produced by weak passing surface troughs, and island effect showers
during the afternoon hours.

&&

.Marine...
Light to gentle trade winds will persist through the beginning of
next week. Combined seas of 3 to 5 feet will persist through the work
week, with the slightest decrease to 3 to 4 feet for the weekend.
There will be a moderate risk of rip currents along north facing
reefs of the Marianas through Thursday night, which could then become
low along all reefs for the weekend. There will also be a moderate
risk of lightning through Friday.

&&

.Eastern Micronesia...
Majuro:
The forecast challenge this afternoon was the widespread convection
from Majuro eastward, which developed along the ITCZ (Inter-Tropical
Convergence Zone), which featured not only great surface convergence,
but it also had good moisture depth through 50k feet and PWATs
(Precipitable Water Values) of 2.7 to 3 inches (locally higher). This
region is also currently in the right entrance region of an upper-
level jet streak. Although cloud top temperature`s are currently
warming, this is expected to be short-lived as this area of
convection has been cyclic the past 36 hours. What`s more concerning
has been cloud top temperatures have consistently pushed -85 deg.
Celsius during this time, with forecast soundings showing winds of
30 to 40 knots just off the ocean surface later tonight into
tomorrow, especially near the eastern atolls. This would potentially
allow for a downburst event or two to occur as entrainment of these
winds get mixed down as the strong ascent creates a favorable
updraft/downdraft couplet for enhanced momentum transfer processes to
occur.

As such, we opted to go with widespread shower coverage, mentioning
locally heavy rainfall, and wind gusts to 30 kt/35 mph. An isolated
gust near 40 mph is not out of the question! This potential looks to
peak during the night (during the diurnal max in the convective
cycle in the tropics), but we carried such wording into the morning
hours to allow for a "buffer zone" temporarily (time-wise). Showers
should become isolated during the afternoon under abundant cloud
cover. Rainfall potential will then decrease Thursday and Friday as
the ITCZ weakens/fragments, with the first portion lifting away from
the region to the north and west. However, another trough in the
trades arrives for your weekend, once again increasing your rainfall
potential.

Pohnpei and Kosrae:
The ITCZ currently extends from near Kwajalein to Kosrae to Nukuoro.
This feature is forecast to lift north and west through the weekend,
weakening as it does so. That spells mainly isolated showers being
the most you can hope for, but a brief period of scattered showers
isn`t totally out of the question as the models sometimes are off on
the timing and strengthen of ITCZ formation/weakening.

Marine wise, look for light to gentle winds to continue outside of
convective influences. Seas of 3 to 5 feet will continue through the
weekend, possibly increasing by a foot or two sometime during the
first half of next week.

&&

.Western Micronesia...
A largely disorganized tropical disturbance embedded within an east-
west oriented trough spanning much of western Micronesia, is expected
to bring a period of heavier showers and thunderstorms to Yap
tonight, and to Palau through Thursday night. Some of these showers
may bring gusty conditions during the heaviest rainfall. Conditions
are expected to improve considerably once the aforementioned
disturbance continues moving west and exits the region, allowing a
ridge to build in and bring isolated to low-end scattered showers
through the weekend. At Chuuk, a drier cycle will ensue the next
several days, followed by a return of patchy showers and some
thunderstorms early next week.

Combined seas of 3 to 5 feet are expected at all three coastal
waters, as multiple weak swells continue to mix in across the region.

&&

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

$$

Marianas: Bowsher
East Micronesia: Doll
West Micronesia: Montvila