234
FXPQ50 PGUM 061940
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
540 AM ChST Sat Jun 7 2025


.Marianas Update...
There were no significant changes made to the forecast overnight.
Showers and thunderstorms are expected to build over for the Marianas
today. Model guidance suggests that the Tropical Upper Tropospheric
Trough (TUTT) will remain in the area for a bit, while the surface
level convergence and troughs will diminish. This is anticipated to
bring a drier weather pattern for Sunday onward. However, with the
TUTT remaining in the area it won`t take much to bring scattered
showers back into the forecast. Altimetry shows combined seas are 3
to 4 feet, and both Ipan and Ritidian buoys confirm these heights.
The risk of rip currents remains moderate along east facing reefs and
low on all other reefs.

&&

.Fire weather Update...
2.21 inches of rain fell yesterday at the Guam International
Airport, which allowed the KBDI to drop to 405, allowing the fire
danger to drop to moderate. As such, critical fire weather
conditions are not likely to return at this time as we transition
toward a wetter seasonal pattern.

&&

.Tropical Systems Update...
Invest 93W is still rated sub-low, unlikely for development, but
continues to be monitored. It is difficult to define on satellite
and scatterometry data, but the recent coordinates on 93W places it
near 12.6N and 137.7E, north of Yap. 850mb vorticity shows this
feature has shifted northwest slightly. Latest model guidance not
showing much development of 93W and conveys a possibility of getting
absorbed into 92W near the Philippines. There is currently a high
level of uncertainty with 93W. This system will be monitored closely
over the next few days.

.Eastern Micronesia Update...
Satellite shows patchy showers across the region this morning. A
disturbance southwest of Pohnpei is generating a little more showers
nearby. Kept scattered showers for Pohnpei, but decreased showers to
isolated for Kosrae, increasing to scattered this evening.
Convection along a trough northeast of Majuro is showing signs of
weakening, so only isolated light showers expected for Majuro today.

Benign marine conditions continue. Buoy and scatterometry data shows
combined seas are 3 to 5 feet and light to gentle winds.

&&

.Western Micronesia Update...
The monsoon trough and embedded disturbances continues to usher in a
monsoonal moisture into the Yap and Palau. The deepest convection is
currently west of Palau, although model guidance shows periods of
enhanced convergence over the islands the next couple days. Only made
minor edits to the forecast to convey a mixture of scattered to
numerous locally heavy showers today. Meanwhile at Chuuk, a decent
area of showers is building to the southeast, however, the
disturbance to southwest is expected to undergo a weakening trend
today. Chuuk will still see scattered showers today, but may expect
see showers start to trend down in the afternoon/evening time.

Scatterometry data shows light and variable winds near Yap and Palau,
with moderate to fresh winds indicated near heavier showers. Light to
gentle winds are seen over Chuuk Lagoon, with an area of moderate
winds southeast of coastal waters.

&&

.Prev discussion... /issued 628 PM ChST Fri Jun 6 2025/

Marianas Synopsis...
Latest satellite imagery shows mostly cloudy skies across the
Marianas, with scattered showers just east of Tinian and Saipan, and
isolated showers over Guam and Rota. A surface trough is evident to
the south of Guam, moving north-northwest toward the islands. Buoys
show seas between 3 and 5 feet.

Discussion...
Guam saw scattered to numerous showers earlier today associated with
the Tropical Upper Tropospheric Trough (TUTT) and a band of
convergence associated with a weak trade-wind trough west of the
islands. This trough has moved out of the area and convection has
decreased significantly across Guam this afternoon. A small band of
scattered showers is also seen just east of Tinian and Saipan this
afternoon and is expected to move through both islands tonight.
Later this evening, another trough, currently south of Guam, will
move toward the islands, bringing increased convection to Guam and
Rota tonight, and to all the islands and waters Saturday. Due to the
unstable conditions associated with the TUTT, thunderstorms remain a
possibility. An unsettled pattern will then remain across the
Marianas for a couple of days as the TUTT remains over the area along
with weak troughs moving through.

Marine...
Marine conditions look to remain fairly benign, other than expected
convection. Gentle to moderate winds will subside to mostly gentle
for Guam and Rota Saturday, and for Tinian and Saipan Sunday night.
Combined seas of 3 to 5 feet will subside to around 4 feet Saturday
for Guam and Rota, and continue between 3 and 5 feet through the
middle of next week for Tinian and Saipan. A west to southwest
monsoon swell will arrive in the Mariana waters early next week.

Fire weather...
Wetting rains have greatly decreased the fire weather threat for Guam
over the last few days. The KBDI is currently sitting at 620 and will
drop significantly again on Saturday, since Guam International
Airport received 2.20 inches of rain so far, with more rain expected
overnight. The KBDI will drop well into the moderate category,
reaching at least 404, lower if more rainfall is received overnight.

Tropical systems...
The weak tropical disturbance, Invest 92W, is now west of 130E,
moving toward the Philippines. Another weak disturbance, Invest 93W,
is centered near 12N138E. This is a broad disturbance at this time
and is not expected to strengthen much, if at all, over the next day
or two. Latest model guidance differs on the expectations for 93W.
The GFS shows 93W becoming more organized late in the weekend into
the beginning of next week, while the ECMWF maintains the system as a
trough with little or no development through the coming week. There
is currently a high level of uncertainty with 93W. This system will
be monitored closely over the next few days.

Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) has dissipated and shower
coverage has diminished significantly for Pohnpei and Kosrae.
However, a broad buffer circulation to the south will slowly drift
west along the Equator through the weekend. This will help increase
convergence along its northern and eastern periphery, with low-end
scattered showers possible for Kosrae through Saturday night and
through Monday for Pohnpei. For Majuro, isolated trade showers are
expected through Sunday. Next week, all three forecast points could
see a chance of showers (probability of precipitation 30 percent) and
a slight chance of thunderstorms as the ITCZ or trade convergent
zone builds into eastern Micronesia, beginning Sunday night at
Majuro, Monday night at Kosrae, and Wednesday at Pohnpei.

Light to gentle winds should prevail through the weekend. Winds could
become moderate with fresh gusts near showers tonight for Pohnpei as
the weak circulation passes to the south. Combined seas of 2 to 4
feet continue through Monday as wind waves and trade swell have
subsided. Winds and seas look to rise beyond Monday as the trade
flow and a background southerly swell increase.

Western Micronesia...
An unsettled weather pattern remains in store for Palau and Yap for
this weekend, as a series of southwesterly monsoon surges will
continue to pummel both Palau and Yap.

Now that Invest 92W has left the region to the northwest, a seasonal
southwesterly monsoon trough has settled across Palau and Yap.
Heavier weather is still expected through Saturday at Palau, and
through Saturday night at Yap, with occasionally very strong gusts
expected near these showers. Conditions are expected to improve
considerably thereafter, with a return to patchy showers and gentler
winds for much of early next week. At this time, mudslides continue
to be unlikely; however, if soils become saturated, any additional
rainfall may quickly become runoff and increase mudslide risks,
especially at Palau.

At Chuuk, patchy showers and some thunderstorms brought by gentle to
moderate trades are expected through Saturday, followed by a period
of drier weather in the first half of next week.

While trade swells have weakened, localized wind waves and a
developing southwest swell will continue to produce choppy seas in
Palau and Yap coastal waters through at least the first half of next
week. Surf will continue to increase along south and west facing
reefs of Palau and Yap, but are not likely to become hazardous at
this time. For now, expect 3 to 5 foot seas for the next few days,
occasionally being a foot or two higher through the weekend.
Meanwhile at Chuuk, seas of 3 to 5 feet will persist for much of next
week.

&&

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

$$

Marianas Update: Bowsher
East/West Micronesia Update: Cruz
Marianas/Tropical: Kleeschulte
East Micronesia: Slagle
West Micronesia: Montvila