543
FXPQ50 PGUM 032111 AAA
AFDGUM

Area Forecast Discussion...UPDATED
National Weather Service Tiyan GU
711 AM ChST Sat Oct 4 2025

.Update...
Converging inflow toward Invest 94W is generating scattered showers
and isolated thunderstorms across the region. Most of the convection
remains just east of the islands and over the eastern waters.
Convection continues to develop over the waters and will reach the
islands very soon.

&&

.Prev discussion... /issued 538 AM ChST Sat Oct 4 2025/

Marianas Update...
Weather radar shows isolated showers within the Marianas Waters, with
scattered showers just to the east. The scattered showers have been
creeping closer. If they get too close they will choke off the
sunlight for the island convection; in that case though, everyone
will have scattered showers. That, in a nutshell, is the forecast
problem of the day. For now maintained continuity with the island
convection favoring previous package, because the high res models
still lean that way. It`s going to be close though.

Tropical Systems...
Invest Area 94W is shown by ASCAT data to be near 22N and 145E, or
almost directly north of Guam (well north). 94W is slowly
consolidating, and is generally well liked by the models in the
medium to long term. Therefore the Joint Typhoon Warning Center has
upgraded it to a Low probability of becoming a tropical cyclone
within the next 24 hours. This means that development is expected,
but will most likely take longer than the 24 hour time span. For
further information on 94W, please refer to the Significant Tropical
Weather Advisory from the Joint Typhoon Warning Center at WMO header
ABPW10 PGTW.

Eastern Micronesia Update...
Trade-wind troughs and a fragmented ITCZ continue to affect Eastern
Micronesia. The forecast was holding up well, so no changes were
needed.

Western Micronesia Update...
A trough extends down from Invest Area 94W toward Yap and Koror,
Palau. Chuuk will be affected by the same trade-wind trough that is
affecting Pohnpei in Eastern Micronesia. This was all handled well in
the previous package, so no updates were needed.

Prev discussion... /issued 624 PM ChST Fri Oct 3 2025/

Marianas Synopsis...
Satellite imagery shows partly cloudy skies, while radar imagery
shows isolated showers over the Marianas. Altimetry shows combined
seas of 2 to 4 feet, while buoy data shows sea heights of about 2 to
3 feet.

Discussion...
Island convection is expected to be the main concern for the next few
days due the the light and variable winds that are expected. This is
expected through the weekend until the trade-wind trough that is
currently north of Pohnpei Island moves into the region. This trough
is expected to bring scattered showers and isolated thunderstorms to
the region. The arrival time of this trough is around the beginning
to middle of next week. Pleasant weather may return once this trough
passes.


Marine...
Light winds and combined seas of 2 to 4 feet are expected through
Wednesday. Winds will become light to gentle Monday. An approaching
TUTT cell is expected to increase the risk of thunderstorms across
the waters over the next couple of days. Island heating could give
rise to thunderstorms near Guam for Saturday and Sunday afternoons.
There will be a low risk of rip currents along all reefs of the
Marianas through the end of next week. There will also be a moderate
risk of lightning on Saturday through Tuesday for Guam.

Tropical Systems...
There is a weak circulation within a broad, elongated trough centered
near 20N147E just north-northwest of the northern CNMI, which is
being monitored by the Joint Typhoon Warning Center (JTWC) as Invest
94W. 94W is categorized as a sub-low, meaning development into a
significant tropical cyclone is not expected within the next 24
hours. There is a broad area of enhanced 850 mb vorticity co-located
with the disturbance, but the overall system remains highly
disorganized. Numerous heavier showers are seen within the area of
convergence along 94W`s eastern flank, with just isolated to
scattered showers seen near the center, mainly just to its north. 94W
looks to gradually shift westward over the next day or so as it
morphs into a broader cyclonic turning over the eastern Philippine
Sea, merging with a weaker circulation currently centered near Yap.
Invest 94W and the emerging pattern over the Philippine Sea will
continue to be monitored for development over the next few days.

Eastern Micronesia...
An active pattern is seen across eastern Micronesia this afternoon. A
fragmented Inter-Tropical Convergence Zone (ITCZ) is seen across the
region, stretching from Pohnpei, across Kosrae to end south of
Kwajalein. Two robust trade-wind troughs are interacting with the
ITCZ to generate numerous showers and isolated thunderstorms across
Kosrae and widespread showers and isolated thunderstorms across
Pohnpei. Kosrae is currently on the eastern edge of the numerous
showers, with convection expected to decrease through the evening,
becoming scattered by midnight, then isolated Saturday afternoon.
Pohnpei looks to keep widespread showers through the night, with
coverage becoming scattered by Saturday morning, then isolated by
afternoon. These changes are due to the troughs moving out of the
region and the ITCZ drifting northward and weakening. For Majuro,
isolated showers this afternoon look to increase to scattered with
isolated thunderstorms during the evening as a weak trough that
crossed the Date Line approaches the atoll. Increased convection is
seen to the east, approaching the atoll. All three points then look
to remain dry for a short time. Then, a series of weak troughs will
bring increased convection to the region Sunday into next week.
Majuro looks to begin to dry out early next week, with Kosrae
following suit by midweek.

Benign marine conditions look to continue into the middle of next
week, with combined seas at or below 5 feet and mostly light to
gentle winds across the region.

Western Micronesia...
The trough moving northwest across far western Micronesia yesterday
has merged with a broad, very weak circulation currently centered
near Yap at around 10N137E. An elongated trough extends far north-
northeast from this feature, passing west of the Marianas where it
connects with Invest 94W at around 20N147E, north-northwest of the
northern CNMI. The circulation near Yap is convectively quiet this
evening. Satellite shows isolated to scattered showers across the
area including over Yap and Palau coastal waters, but most of the
convection is well northwest of the circulation center where
convergence is strongest. Models show little strengthening of this
feature over the next few days as it begins to morph into a much
broader cyclonic turning over the eastern Philippine Sea, where
Invest 94W looks to make up the northern periphery of the broader
circulation. This will support the strengthening of a southwest
monsoon pattern over Yap and Palau early next week, leading to wetter
conditions Monday through Wednesday. Showers will become numerous at
times, mainly for Yap, with locally heavy showers possible. In the
meantime, just isolated to scattered showers will continue through
the weekend.

To the east, widespread cloudiness is seen across Chuuk State
extending across much of eastern Micronesia, with the highest cloud
tops and heaviest showers well east of Chuuk Lagoon and adjacent
waters. Showers are expected to remain scattered for Chuuk overnight
with numerous showers further east. This weekend, a tropical
disturbance looks to develop just east of Chuuk, shifting northwest
across the area through early next week as it passes near the
Marianas. Model trends have been keeping Chuuk along the periphery
of the developing disturbance, but locally heavy showers will be
possible through the weekend. Scattered showers will continue through
early next week as a fragment of the ITCZ lifts northwest into the
area.

Benign marine conditions continue. Altimetry data indicates combined
seas of around 2 to 4 feet across the region, comprised of a primary
northeast to east trade swell. There is little change expected
heading into the weekend. Early next week, a pulse of elevated
southwest swell looks to build across Palau waters, driven by a
developing monsoon-like pattern, but no marine or surf hazards are
expected at this time. Winds will remain mostly light to gentle
through the weekend, becoming moderate at times early next week as
the monsoon-like pattern strengthens.

&&

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

$$

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