492
FXPQ50 PGUM 201739
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
339 AM ChST Sat Sep 21 2024

.Marianas Update...
Only minor changes were needed tonight. The main change is for a
passing weak trough that is anticipated to pass during the AM hours.
Showers were increased to scattered and lightning potential
increased to isolated as this trough has produced lightning already.
This may not come to pass as many times showers look promising as
they pass in to the coastal waters, then fizzle out. The other change
was removing the secondary swell from the forecast for tonight
onwards as it has became so minor that it will have no impacts on the
seas and surf.

&&

.Eastern Micronesia Update...
Only minor updates made to the forecast this morning. The ITCZ
(Inter-Tropical Convergence Zone) and embedded troughs continue to
drift northwest across the region, bringing scattered showers and
isolated thunderstorms to Majuro, Kosrae and Pohnpei. The ITCZ and
troughs will shift north and dissipate by late weekend, and a drier
trade-wind pattern expected for most of next week.

Benign marine conditions will continue with combined seas 2 to 4 feet
and light to gentle trade winds into early next week. Seas and winds
could dip slightly around the middle of next week as surface ridging
settles over the region.

&&

.Western Micronesia Update...
Only minor changes were made to the forecast for Yap and Palau.
Scattered showers and isolated thunderstorms possible at times
through the weekend into early next week as another surface trough
slowly lifts northwest through the region.

Scattered showers and isolated thunderstorms possible for Chuuk
today as the ITCZ and surface trough passes through. As the trough
and ITCZ drift northwest, shower and thunderstorm potential diminish
as surface ridging build in.

Benign marine conditions expected with light to gentle winds and
combined seas 2 to 4 feet. Seas look to dip about a foot for next
week.

&&

.Prev discussion... /issued 538 PM ChST Fri Sep 20 2024/

Marianas Synopsis...
Fair weather is seen across the area with some showers seen to the
northwest near an upper-level low. Isolated showers are seen to the
east, so expect continued fair weather for the Marianas tonight and
tomorrow.

Discussion...
The Tropical Upper Tropospheric Trough (TUTT) continues to move west
with isolated thunderstorms associated with it also moving away from
the region. Fair weather will continue tonight and tomorrow as a
ridge passes through the region and we may see a few passing showers,
isolated at most, coming from the narrow band of showers further
east shown on visible satellite. Next period of showers activity is
expected to be around late next week as a monsoon trough develops,
but may it may start affecting the Marianas early next week if the
monsoon trough develops according to the ECMWF model. Showers are
expected to be low-level scattered showers based off the latest model
guidance. Winds are expected to be variable as the trough axis
develops right across the Marianas region.

Marine...
Coastal buoys are reporting 3 to 4 foot seas with west swell
continuing to abate. Expect seas to build slightly to 4 to 5 feet on
Sunday due to a building east swell. Gentle trades are expected
through the weekend. Rip risk remains low for tonight and tomorrow,
possibly becoming moderate on Sunday for east reefs.

Eastern Micronesia...
The ITCZ (Inter-Tropical Convergence Zone) remains the main feature
across eastern Micronesia this afternoon. There are currently two
fragments of the ITCZ, one over the far western portion of the
region, extending eastward from near Chuuk to south of Pohnpei and
Kosrae. The second branch is seen across Kwajalein and Majuro to east
of the Date Line. Along with the ITCZ, there are a few weak trade-
wind troughs interacting with the ITCZ. The first one is just east of
Pohnpei which looks to move over Pohnpei later this evening, pulling
the ITCZ a bit north resulting in increased showers and isolated
thunderstorms developing over the state during the evening. The next
one is seen just east of Kosrae. This trough also looks to bring
increased convection to Kosrae near midnight. The last one is seen
east of Majuro. This is the most robust of the troughs and looks to
bring a period of numerous showers and isolated thunderstorms to
Majuro as it interacts with the ITCZ. As the three troughs progress
and the ITCZ dissipates, Majuro will see the first decrease in
convection. By Saturday night, expect a dry trade-wind pattern to
move in to the Marshalls. model guidance is showing a prolonged drier
pattern over the Marshalls through at least the end of next week.
The drier pattern will spread westward over the weekend, with
Pohnpei see the dry pattern Sunday night. Kosrae will keep scattered
showers the longest as the last trough moves through the state but
turns more northwest, toward the Marianas. By Monday, Kosrae will
also move into the prolonged dry pattern. For those in Pohnpei,
Kosrae and the Marshalls that depend on catchment water, this may be
a good time to consider conserving as much water as possible, maybe
additional storage, if available.

Benign marine conditions will continue through at least the middle of
next week, with mostly light to gentle winds across the region and
seas of 2 to 4 feet. Majuro, however, could see occasional moderate
winds tonight.

Western Micronesia...
Only minor changes were made to the forecast. Scattered showers were
reduced to isolated for Yap and Palau tonight through Saturday. This
was based on the current trough near Yap remaining devoid of
convection as well as guidance showing the leading edge of convection
across eastern Yap State dissipating before approaching Yap Proper.
Scattered showers should return Sunday into Sunday night when the
trough just west of Weno approaches Yap and Palau.

Not much change was made to Chuuk`s forecast. Scattered showers are
expected to continue during the ITCZ flare up tonight and Saturday
before precipitation chances decrease to isolated Saturday night and
into the first half of the week.

Benign marine conditions will continue through the period. Combined
seas will be between 2 and 4 feet for the next several days. Winds
will remain gentle to moderate through much of the week as well.

&&

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

&&

$$

Marianas: Bowsher
Micronesia: Slagle