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AXPQ20 PGUM 240145
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1145 AM ChST Sat May 24 2025

Tropical Weather Discussion for the Western North Pacific between
the Equator and 25N from 130E to 180. The following information is
based on recent satellite imagery/data, weather observations, radar,
and meteorological analysis.

...SPECIAL FEATURES...

None.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
There are eight notable trade-wind troughs visible on satellite data
this morning. The first trough enters the region near 3N130E and
extends northeast through the Republic of Palau and ends near Yap
Proper. The second trough is east of Yap Proper, extending from just
south of Sorol to the northeast of Gaferut in Yap State. Together,
these troughs are producing scattered showers and isolated
thundestorms across most of the Republic of Palau and Yap State.
Models show these two troughs morphing into a broad trough/disturbance
across Palau and far western Yap State, producing scattered to, at
times, numerous showers and isolated thunderstorms across the area
through Sunday and then shifting west of the region early this
upcoming week. Weak trade-wind convergence is expected to develop
east of these troughs producing spotty showers over eastern Yap
State.

The third trough extends northward from the northern coastal waters
of Kosrae to 9N164E, producing scattered showers along the trough
axis, with very little lightning detected by the Global Lightning
Detection (GLD) network within the ongoing convection. However, the
leading edge of the convection is moving at around 25 kt (~29 mph),
so some gusty winds and choppy seas are expected within the
convection associated with the trough. Models show this trough
shifting towards Pohnpei later today and into tonight but with a
slight weakening trend, which may limit the potential for scattered
showers, isolated thunderstorms, and gusty winds across Pohnpei State
as this trough moves through.

The fourth trough is located west the northern Mariana Islands, while
the fifth trough is moving in the northern islands. The trough
well west of the Marianas is centered near 19N139E and is mainly in
the open waters of the Philippine Sea, producing a few thunderstorms
with occasional to frequent lightning over the past couple of hours,
according to the GLD network. This is likely due to the upper-level
divergence associated with an upper-level low that is entering the
region near 24N138E. As this trough drifts westward, it will remain
out in the open waters of the Philippine Sea, but it will leave the
support of upper-level divergence of the upper-level low, decreasing
the intensity of thunderstorms within the trough. The trough moving
through the Marianas extends from near Anatahan and up the island
chain ending to the north of Farallon de Pajaros near 22N146E.
Scattered showers and isolated thunderstorms extend across most of
the northern Islands, but do become more spotty near and north of
Asuncion and Maug. As this trough shifts westward, thunderstorms may
increase in coverage and intensity as it moves towards the upper-
level low near 24N138E, that is currently supporting thunderstorm
development in the trough west of the Marianas.

Troughs six and seven are located north-northwest of Wake Island and
east of Wake Island, respectively. The trough north-northwest of
Wake Island is what remains of the surface low discussed in previous
discussions, and does not have much convection associated with it.
This trough is expected to slowly dissipate over the next couple of
days. The final trough extends northward from north of Bikini Atoll,
near 13N166E, and ends near 25N171E. Scattered to numerous showers
and isolated thunderstorms extend along this trough axis, supported
by a TUTT cell located north of the region. This trough will shift
west towards Wake Island, increasing showers and thunderstorms over
the island Sunday and Sunday night.

TUTT...
The Tropical Upper Tropospheric Trough (TUTT) extends from an upper-
level low near 28N168E to another upper-level low near 20N148E and
ending near 15N130E. Scattered showers and isolated thunderstorms are
seen across the Northern Marshall Islands, east of Wake Island, and
the northern CNMI, mainly associated with the upper-level lows and
the trade-wind troughs discussed above. There is another upper-level
low, located near 23N138E, that was north of the region and has
shifted southward. Models have this low slowly morphing with the
upper-level low in the northern CNMI over the next couple of days.
The upper-level lows are expected to slowly shift westward, keeping
the TUTT across the northern portion of the region between 20N and
25N. The greatest potential for thunderstorms will be on the eastern
edge of the upper-level lows where they bisect surface features such
as troughs and trade convergence.

OTHER SYSTEMS...

TRADE CONVERGENCE...
A band of trade convergence extends eastward from east of Saipan
near 16N146E to 14N159E, creating scattered showers and isolated
thunderstorms between 14N and 16N. This area of convergence is
expected to shift westward into the Marianas later this weekend and
into the upcoming week, with models showing the best potential for
showers and thunderstorms from just north of Rota and up to Alamagan,
but this may change depending on any southward or northward shifts
of this area of convergence.

A second area of trade convergence is developing near Majuro and
extends eastward to the Date Line, with spotty to low-end scattered
showers extending along this band of convergence in a broader area
between 3N and 9N. Models shows this area of trade convergence
shifting west-southwest increasing the potential for showers and
even thunderstorms across Kosrae and southern Pohnpei State over the
next couple of days, while Majuro may see a drying trend Sunday night
as convection shifts with the trade convergence and away from the
atoll.

$$

Schank