801
FXPQ50 PGUM 261942
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
Issued by National Weather Service Honolulu HI
542 AM ChST Fri Jun 27 2025

.Marianas Update...
Showers have trended significantly downward across the Marianas
overnight, with radar showing some stratiform remnants over mainly
Rota coastal waters and westward. Surface observations reveal mostly
gentle to moderate southeast flow across the islands, with frequent
fresh gusts over Guam. Overnight scatterometry shows a relatively
narrow band of fresh southeast winds extending out from Guam and
Rota toward the northwest. Given radar, satellite, and latest model
trends, Probability of Precipitation (PoP) was decreased to 40%
across the Marianas for today, but increased back up to 60% for Guam
and Rota and 50% for Tinian and Saipan tonight, as Invest 97W helps
maintain a moist, somewhat convergent southeast to south flow across
the area as it moves further away. A wet pattern will continue
through the weekend and a Flood Watch remains in effect through late
Sunday night, but the potential for widespread heavy rainfall looks
to be diminishing.

&&

.Marine Update...
There was little change in the overnight marine forecast. A gentler
south to southeast flow will prevail across the Marianas through
Saturday as Invest 97W, centered west of the Marianas near 16.0N
140.1E, shifts further away. Combined seas of 4 to 6 feet for Guam
and Rota, and 5 to 7 feet for Tinian and Saipan, look to build late
weekend into early next week as a monsoon swell begins to build into
the region. This looks to be in response to another possible
disturbance developing east of the Marianas, leading to a moderate to
fresh southwest flow, but there is still significant disagreement
between models. ECMWFwave keeps the stronger monsoon swell energy
just further west of the Marianas, which would instead maintain a
steadier east to southeast swell through early next week.

&&

.Hydrology Update...
Yesterday`s heavy, widespread showers led to rainfall totals of 5.37
inches recorded at the Guam International Airport. Showers have
since greatly diminished across the Marianas overnight, but an
overall wet pattern will continue over the next few days as Invest
97W helps maintain a moist southeast to south flow across the
islands. Another inch or two of rain is possible through the weekend
with locally heavy showers possible, but the threat for flooding
across the islands looks to be diminishing as 97W weakens. Residents
in the Marianas, especially those in flood-prone areas, should
continue to monitor for updates.

&&

.Tropical systems Update...
Invest 97W is currently located near 16N140E, west of the Marianas.
97W is currently rated low by the Joint Typhoon Warning Center (JTWC),
meaning that development into a significant tropical cyclone is
unlikely within the next 24 hours. Moderate to deep convection is
occurring near the center and within the convergent southeasterly
flow to the southeast, with most of the convection focused west of
Guam coastal waters. 97W has shifted further west and north of the
Marianas with little discernible organization at the surface, and
model trends have it developing slower and further to the northwest,
increasingly away from the Marianas.

&&

.Eastern Micronesia Update...
There was little change in the overnight update. An Intertropical
Convergence Zone (ITCZ) disturbance has been flaring up just east of
Kosrae with moderate to deep convection building west-northwest over
the area. Meanwhile, a broad embedded trough within the ITCZ is
maintaining a band of showers over much of Pohnpei State further
west. For Majuro, satellite and GLD network data reveal showers and
thunderstorms building nearby within a region of enhanced
convergence. PoPs of 50 percent were maintained at Pohnpei and Kosrae
with 40 percent for Majuro today as these features gradually shift
west through the area, with decreasing showers over the next few days
as the ITCZ dissipates. Gusty winds will be possible at times near
heavier showers, especially in the morning near Kosrae and Majuro.

Seas across the region remain a mixture of trade swell and
southeasterly swell, with buoys showing combined seas of around 4 to
6 feet for Pohnpei and Kosrae, increasing to around 7 feet further
east near Majuro.

&&

.Western Micronesia Update...
Little change to the forecast. A mostly gentle southwest monsoon flow
prevails across Palau and Yap, with isolated to scattered showers
across the region, mainly within an area of weak troughing near and
north of Yap Proper. Shower potential increases later in the weekend
as the monsoon pattern strengthens across far western Micronesia, to
the south of a slowly developing Invest 97W. This may lead to
moderate to fresh southwest flow by around Sunday, but in the
meantime, winds will be light to gentle, with 2 to 3 foot seas near
Palau and Yap. To the east, scattered to numerous showers are seen
within an ITCZ disturbance centered north-northeast of Chuuk Lagoon.
This disturbance looks to maintain at least scattered showers near
and north of Chuuk Lagoon over the next day or so before shifting
further away to the north. 3 to 5 foot seas will continue near Chuuk
for the next few days, decreasing slightly later in the weekend as
the trade swell diminishes slightly.

&&

.Prev discussion... /issued Issued by National Weather Service Honolulu HI/

Marianas Synopsis...
Satellite and radar are showing cloudy skies and numerous showers
over the Marianas. Rainfall reports of 3 to 5+ inches were
commonplace today. Nearby buoys are indicating seas of 4 to 6 feet.

Discussion...
Moist, convergent flow along the eastern edge of the monsoon trough
and developing tropical disturbance (Invest 97W) will persist over
the Marianas. Latest deterministic and ensemble model guidance have
trended towards 97W developing slower and tracking further west of
the Marianas. While this casts doubt on the potential for wind
hazards, the continuing expectation is for a very wet period to
continue through the weekend. High-end scattered to numerous showers
and isolated thunderstorms are expected, with locally heavy downpours
possible. A Flood Watch remains in effect through Sunday night. Into
next week, models differ quite a bit, but the general trend is for a
monsoon flow to develop over the Marianas, with a increased chance
of showers and thunderstorms continuing.

Marine...
Gentle to moderate winds for Guam and Rota tonight, and moderate to
fresh for Tinian and Saipan, will diminish and become more southerly
Friday. Through the weekend, a tropical disturbance, Invest 97W, is
expected to develop west of the Marianas, bringing heavier showers
the next few days. Combined seas of 3 to 6 feet for Guam and Rota and
4 to 7 feet for Tinian and Saipan, look to build late weekend into
early next week as the monsoon swell builds into the region as 97W
departs. Winds also look to become southwest moderate to fresh.

There will be a moderate risk of rip currents along east and south
facing reefs of the Marianas for the next few days. Surf could rise
along south and west facing reefs late weekend into early next week
with the potential for an elevated southwest monsoon swell.

Hydrology...
The monsoon trough and developing tropical disturbance, Invest 97W,
are expected to bring widespread showers through the weekend.
Rainfall amounts today have totaled 3 to 5+ inches already. Total
rainfall amounts of 5 to 10 inches are expected through the weekend,
with locally heavy amounts possible, mainly across Guam and Rota.
This rainfall is expected to produce minor flooding across the
islands, with flash flooding possible in the areas of heavier
rainfall.

Residents in the Marianas, especially those in flood-prone areas,
should monitor this developing weather pattern closely as advisories
and warnings could be issued late this week.

Tropical Systems...
Invest 97W is west of the Marianas, centered near 16N142E. 97W is
currently rated low by the Joint Typhoon Warning Center (JTWC),
meaning that development into a significant tropical cyclone (TC) is
unlikely within the next 24 hours. Moderate to deep convection is
occurring near the center and to the north and east where convergent
southerly and easterly flow meet, including over the Marianas. Much
uncertainty in the track and development of Invest 97W still
persists, but latest deterministic and ensemble model guidance have
trended towards 97W developing slower and tracking further west of
the Marianas.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) has drifted north over
Pohnpei and Kosrae to just south of Majuro. Have increased showers
coverage to numerous and locally heavy for Pohnpei and Kosrae
tonight. Showers expected to increase in coverage for Majuro tonight
as the ITCZ lifts north, but keep coverage scattered. Scattered
showers and isolated thunderstorms are expected through Friday night
with probability of precipitation (PoP) of 40 to 50 percent. Gusty
winds will be possible at times near heavier showers. The ITCZ is
expected to dissipate, and mainly isolated to low-end scattered
showers are expected over the weekend. Showers and thunderstorm
chances increase early next week as the ITCZ looks to re-establish
itself over eastern Micronesia.

Regional seas will remain a mix of trade and SE swell. Seas will
range between 4 and 6 feet for Pohnpei and Kosrae. Slightly higher
trade swell is likely for well-exposed waters around Majuro, with
seas up to 7 feet through Friday. Aside from some fresh winds tonight
at Majuro, winds will generally be gentle to moderate the next few
days. Winds look to increase and become moderate to fresh beginning
Sunday at Majuro and early next week for Kosrae and Pohnpei as the
trade flow strengthens. Residents should be aware of the large tides
the next several days due to the new moon phase despite the fact no
notable swells are currently forecast.

Western Micronesia...
Chuuk remains under a surface trough serving as the boundary between
easterly trades to the east, and west to northwest flow to the west.
This feature will likely trigger bursts of showers and thunderstorms
at times through Friday night. Chuuk conditions will be quite
changeable over the weekend into early next week as the broader
synoptic pattern evolves in response to 97W as it lifts northwestward
the next few days, but generally lower coverage of showers and
thunderstorms expected. Winds will be light to gentle. Seas 3 to 5
feet look to decrease slightly by the weekend as the trade swell
subsides.

Further west, modest monsoon flow will result in scattered showers
(PoPs 30-40 percent) and isolated thunderstorms for Yap and Palau
through Friday. Over the weekend into early next week, the west to
southwest monsoon flow is expected to increase as the a potential
tropical disturbance (Invest 97W) looks to develop west of the
Marianas, but likely staying well north of Yap and Palau, with
showers and thunderstorm potential trending higher. Seas of 2 to 3
feet and light to gentle winds look to continue through the end of
the work week. Winds and seas will trend up through the weekend into
early next week as the monsoon flow increases. Moderate to fresh
winds and seas of 4 to 6 feet are expected by the weekend. Surf also
looks to rise along south and west facing reefs. Residents should be
aware of the large tides the next several days due to the new moon
phase.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...Flood Watch through late Sunday night for GUZ001.

MP...Flood Watch through late Sunday night for MPZ001>003.

Marianas Waters...None.
&&

$$

Marianas Update: DeCou
East/West Micronesia Update: DeCou
Marianas: Slagle
Micronesia: Slagle
Tropical: Slagle