557
FXPQ50 PGUM 070933
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
733 PM ChST Tue Oct 7 2025


.Marianas Synopsis...
Satellite imagery shows cloudy skies, while radar shows isolated to
scattered showers across the region, increasing in coverage to the
northwest. Buoy data shows sea heights of about 6 feet. Altimetry
suggests a bit higher seas at 6 to 7 feet.

&&

.Discussion...
Invest 95W continues to move away from the Marianas to the northwest.
Scattered showers and isolated thunderstorms are expected to linger
tonight. However, pleasant weather is expected for much of the week,
save for one caveat for Thursday. Showers are expected to make a
brief return as a broad surface trough (coming from Yap State)
provides the lift needed to bring showers back to the region. Showers
may be the most dense near Guam and least near Saipan.

&&

.Marine...
Combined seas of 4 to 6 feet are seen over the coastal waters, with
the highest seas in Saipan`s waters and the lowest in Guam`s waters.
Similar scenario for the winds, with gentle to fresh winds across
Tinian and Saipan and light to moderate winds across Guam and Rota.
As Invest 95W pulls farther away from the Marianas, sea conditions
will improve quickly. Over the weekend a north swell is anticipated
to bring sea conditions back up to 5 to 7 feet. There is a moderate
risk of rip currents along north and east facing reefs while south
and west facing reefs remain low. The surf is expected to continue to
diminish through the workweek. Looking towards the weekend, wave
models show a long-period north swell entering the region, likely
generated by Typhoon Halong. Currently, wave models have the swell
increasing to 5 feet on Sunday, causing surf to be slightly elevated
along north facing reefs this weekend, up to around 8 feet.

&&

.Tropical Systems...
Invest 95W is located near 16N143E and has been upgraded to HIGH,
meaning significant tropical cyclone development is likely within 24
hours. This system is about 200 miles northwest of Guam and 190
miles west-northwest of Saipan. Maximum sustained winds are around 18
to 23 knots, and 95W is showing signs of becoming better organized
with deep convection building along the southwest and northern
sectors. Model guidance indicates 95W will continue moving north-
northwestward, away from the Marianas, and continuing to develop over
the next 48 hours, although maintaining a somewhat asymmetrical wind
field, with stronger winds on the eastern sector.

&&

.Eastern Micronesia...
A broad area of low pressure looks evident north of Kosrae. This
region is also an inflection point on the model-derived wind fields.
It`s not out of the realm of possibilities that this broad
circulation may attempt to organize somewhat as the GEFS indicates,
with the ECENS showing no development at all. Even if you sided with
the GFS ensemble (GEFS) it too washes out any development in 3 to 4
days, so aside from a short period of increased cloud cover and
slightly higher rainfall potential at Pohnpei and Kosrae, I wouldn`t
expect much with this feature.

The other item of interest is the lack of a clearly-defined ITCZ
(Inter-Tropical Convergence Zone) in the hand analysis (somewhat
better indication) or the model forecasts. This relegates any
increase rainfall potential in the day 3 through 7 portion of the
forecast tied to embedded surface troughs in the trade flow. The GFS
GDI (Galvez-Davison Index) suggests this theme quite nicely as well.
Thus, rainfall potential was "capped" at 40 percent for the
forecast.

As for marine conditions, light to gentile winds will prevail
through the forecast. Seas of 3 to 5 feet will also continue through
Saturday, before increasing for the first half of next week as a
northerly swell arrives and increases.

&&

.Western Micronesia...
Daytime ASCAT analysis did show stronger winds over Palau, so bumped
up the winds tonight, however showers and gusts are expected to
trend down overnight becoming scattered on Wednesday. Included a
headline for locally heavy showers with gusts and choppy seas for
tonight, then convection within the moist southwesterly flow
gradually lessens in western Micronesia as the trough, extending from
Typhoon Halong (northwest of Iwo To) and Invest 95W (near the
Marianas), shifts northwest. For Yap, the bulk of showers are to the
north and northeast, although continue to expect scattered showers
and isolated thunderstorms through Wednesday and Wednesday night.
Around Thursday, southwesterlies weaken and a trade-wind pattern
begins to push in from the east, possibly bringing another period of
scattered showers Thursday night and Friday.

For Chuuk, scattered showers build back in tonight. Satellite imagery
shows patch showers along a weak trade-wind trough approaching Chuuk
this afternoon, but showers are anticipated to increase to high-end
scattered Wednesday night and Thursday as an ITCZ fragment develops.
Models are beginning to hint at a weak trade-wind disturbance over
the weekend, possibly prolonging scattered showers through at least
Sunday.

Scatterometry and altimetry data indicates moderate to fresh
southwest to west winds over Palau and Yap, light to gentle trades
near Chuuk and seas 3 to 5 feet across the region. Choppy seas are
expected near Palau tonight, from stronger outflow boundaries from
heavier showers to the southwest. Winds are expected to decrease back
down to light to gentle late week and over the weekend. A pulse of
southwest swell builds into Palau waters and reaches Yap by Thursday,
driven by a developing monsoon-like pattern. This may lead to surf
along west-facing reefs to build up to 6 or 7 feet along west-facing
reefs Wednesday night or Thursday. This will also cause seas to build
to 4 to 6 feet over the next couple days. Longer- period northerly
swell is expected to move into the region late week and over the
weekend, emanating from Typhoon Halong to the distant north. This
will cause surf to build along north-facing reefs, first to Yap and
Palau, then to Chuuk around Sunday. No marine and surf hazards are
expected at this time.

&&

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

$$

Marianas: Bowsher
Tropical: Bowsher/Cruz
East Micronesia: Doll
West Micronesia: Cruz