914
FXPQ50 PGUM 031939
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
539 AM ChST Wed Jun 4 2025


.Marianas Update...
Not much change to the forecast were needed. Scattered showers and
isolated thunderstorms are anticipated through the rest of the week.
Showers maybe heavy at times, most notably for today. These showers
and thunderstorms are due to a series of surface-level troughs
passing under a Tropical Upper-Tropospheric Trough (TUTT) cell. The
pattern is expected to bring much needed rain to the Marianas over
the week. Combined seas remain around 4 to 5 feet. Risk of Rip
Currents remain moderate. Seas are expected to be choppier near the
heavier showers.

&&

.Fire weather...
0.14 inches of rain fell yesterday at the Guam International
Airport, which allowed the KBDI to drop at 702. This is in the
high category due to winds remaining below the 20 mph threshold.
Winds and RH are expected to remain below Red Flag Warning criteria,
along with more heavier showers that are likely to bring wetting
rains the next few days. As such, critical fire weather conditions
are not likely to return at this time as we transition toward a
wetter seasonal pattern.

&&

.Eastern Micronesia Update...
The Intertropical Convergence Zone (ITCZ) extends into the region
near 5N, passing south of Majuro and ending southeast of Kosrae.
Spotty showers are seen over Pohnpei and Kosrae, with the least
amount of activity over Majuro. Majuro`s 12Z sounding and satellite-
derived precipitable water amounts still show a relatively dry air
mass, around 1.75 inches. No major changes to the forecast through
tonight.

Buoy and altimetry data show combined seas of 4 to 6 feet across
most of the region and up to 7 feet at Majuro. Scatterometry shows
gentle to moderate winds near Pohnpei and mainly moderate winds
across Kosrae and Majuro.

&&

.Western Micronesia Update...
Overnight scatterometry shows an ill-defined circulation in southern
Yap State, near 6N141E. This is becoming the focal point for the
trade-wind convergence pattern to the east and the developing
monsoon pattern to the west. Latest satellite imagery shows cloudy
skies and scattered to numerous showers near Chuuk, and scattered
showers gradually building into the main islands of Yap and Palau.
Saw support in latest model guidance to trend down numerous showers
to scattered this afternoon for Chuuk, however the enhanced trade-
wind convergence following the disturbance to the west is still
expected to keep high-end scattered showers through at least
tonight. For Yap and Palau, no major changes to the overall forecast
trend, but added in a headline to emphasized possible monsoon pattern
late week.

Buoy data shows combined seas 2 to 4 feet near Yap and Palau and up
to 6 feet near Chuuk. Scatterometry data shows light to gentle
west to southwest winds near Palau and northeast winds near Yap.
Gentle to moderate easterly trades continue near Chuuk.

&&

.Prev discussion... /issued 458 PM ChST Tue Jun 3 2025/

Marianas Synopsis...
Gentle to moderate easterlies prevail. Satellite imagery and Doppler
Radar indicate an unsettled pattern producing scattered showers and
thunderstorms across much of the Marianas. The buoys indicate seas
are around 4 feet.

Discussion...
The northerly upper-level jet on the westernmost side of the tropical
upper-tropospheric trough (TUTT) cell has been interacting with
multiple surface troughs, producing scattered showers and some
thunderstorms across the coastal waters of Guam and the CNMI. After a
lull in showers and thunderstorms early this evening, more patchy
but heavy showers and some thunderstorms will develop through early
Wednesday morning as the TUTT cell continues to move in from the
east. A generally wet pattern will persist for much of the week, with
conditions likely to improve by early next week.

Marine...
Combined seas of 4 to 5 feet will persist the next few days,
dropping a foot during the weekend as trade swell and wind waves
diminish slightly. A moderate risk of rip currents is expected along
east facing reefs for much of the week.

Fire weather...
0.02 inches of rain fell since midnight at the Guam International
Airport, with more showers likely to follow tonight. This will allow
the KBDI to drop, which remains at 713. Winds and RH are expected to
remain below Red Flag Warning criteria, along with more heavier
showers that are likely to bring wetting rains the next few days. As
such, critical fire weather conditions are not likely to return at
this time as we transition toward a wetter seasonal pattern.

Eastern Micronesia...
The Intertropical Convergence Zone (ITCZ) stretches across eastern
Micronesia. The ITCZ is well south of Majuro and isolated trade
showers are expected through tomorrow night. The ITCZ looks to
meander north across the atoll late week and looks to bring an
increased potential for showers through Friday. The ITCZ looks to
dissipate again with by the weekend before redeveloping and bringing
another increased potential for showers early next week. For Pohnpei
and Kosrae, the ITCZ will fluctuate through the period with multiple
trade disturbances traversing the region as well. A potential weak
circulation could develop southwest of Pohnpei and Kosrae by late
week, further enhancing the convergence and shower potential. Both
Pohnpei and Kosrae will see scattered showers and isolated
thunderstorms for most of the period, with POPs bouncing mostly
between 30 and 50 percent. Both locations could see brief periods of
isolated showers.

Winds will generally be gentle to moderate through Thursday. Winds
could occasionally become fresh for Majuro, as well as for Pohnpei
and Kosrae with heavier showers and thunderstorms. Winds look to
become light to gentle for Pohnpei and Kosrae and generally gentle
for Majuro by Friday. Combined seas of 4 to 6 feet for Pohnpei and
Kosrae and 5 to 7 feet for Majuro are expected through Thursday,
becoming 2 to 4 feet by the weekend as wind waves and trade swell
subside.

Western Micronesia...
Satellite reveals a relatively quiet regime over far Western
Micronesia this afternoon with a portion of the subtropical ridge
dipping south into the area. Light to gentle winds and partly cloudy
skies prevail with a col set up just south of Palau, with southeast
to south winds for Palau and northeast winds over Yap. To the east, a
wetter pattern is seen across Chuuk State, with a weak ITCZ fragment
and surface trough located just south of Weno, Chuuk, with another
trough just to the northwest.

Quiet conditions are temporary for Yap and Palau as a monsoon
pattern is expected to develop this week. A broad, weak circulation
has begun to form southeast of the area, out of a broad trade-wind
trough located to the south of Sorol and Eauripik in Yap State. This
circulation makes up a portion of the near-equatorial trough (NET),
which extends east-southeast into the region from over southern
Mindanao. Scattered showers are seen across the area, with a
thunderstorm or two along the disturbance`s northern flank where
convergence is stronger.

Deterministic and ensemble model guidance indicate this disturbance
will shift northwest toward the Republic of Palau and Yap Proper as
the broader NET lifts north over the next day or so, and a gentle to
moderate monsoon flow sets up across the region. This scenario would
bring prolonged unsettled conditions over Palau and Yap in the
latter half of the week into the weekend, including locally heavy
rains, isolated thunderstorms, and a possibility for strong gusts.
Southwest to west winds should begin to develop near Palau late
tonight, arriving later to Yap Proper around Thursday or Friday as
the aforementioned disturbance meanders northwest through the area.
Timing and direction of winds and showers will depend on how the
disorganized disturbance holds together as it moves toward the
Philippine Sea. Winds overall look to remain gentle for the next few
days, becoming more gentle to moderate by the weekend, but strong
gusts will be possible with any convective surges. NWS Guam will
monitor this situation carefully, as significant rains will be
possible over Palau and Yap by the end of the week.

Chuuk will remain in an unsettled weather pattern for the next few
days, with increased convergence associated with a disorganized ITCZ
fragment just to the south of Weno. This convergence looks to lift
slightly north and maintain showers and isolated thunderstorms across
the region through midweek, with locally heavy showers expected at
times.

Benign marine conditions continue. Combined seas of 2 to 4 feet
should persist the next few days near Palau and Yap, with 4 to 6 foot
seas near Chuuk gradually coming down over the next few days. In
response to a developing monsoon pattern, a southwest swell looks to
move in across the Republic of Palau beginning Thursday, arriving
later to Yap around Friday. This has the potential to develop
hazardous surf, mainly along south and west reefs of Palau by the end
of the week, and the situation will be monitored carefully.

&&

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

$$

Marianas Update: Bowsher
East/West Micronesia Update: Cruz
Marianas: Montvila
East Micronesia: Slagle
West Micronesia: DeCou