234
AXPQ20 PGUM 160145
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1145 AM ChST Wed Jul 16 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...

TROPICAL AND MONSOON DISTURBANCES...
The Joint Typhoon Warning Center has opened Invest 96W on a
broad circulation in the Philippine Sea, centered near 14N132E,
within the monsoon trough. Scattered heavy showers and isolated
thunderstorms are developing near the center of 96W, with showers
increasing to numerous west of Palau, within the southwest flow
across the Republic of Palau. 96W remains largely disorganized; the
CIMSS Tropical Analysis showing a broad area of vorticity at 850 mb,
centered slightly east of 96W, with the analysis showing two
vorticity lobes at 500 mb, one near 96W and the second further west
and over northeastern Mindanao. Model guidance shows 96W slowly
moving northwest and deeper into the Philippine Sea, exiting the
region as it slowly develops. The potential for development into a
significant tropical cyclone over the next 24 hours is very low.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
The monsoon trough enters the region near 14N130E passing through
Invest 96W, which will become the main feature in the area over the
next few days, ending near Yap at 9N140E. As mentioned above with
96W, scattered heavy showers and isolated thunderstorms are found
along the trough axis around 96W, with showers increasing to
numerous west of Palau. Recent visible satellite imagery shows
outflow boundaries moving at 30 kts (~35 mph) just west of Palau, so
gusty winds at Palau are possible at times today. Near Yap, showers
are isolated this morning, but scattered showers may develop along
the convergent flow along the eastern edge of the monsoon trough. The
monsoon trough will be difficult to distinguish from 96W as it
develops the next several days, but should keep the monsoonal
pattern over the Republic of Palau for some time near the edge of
the showers and thunderstorms that are developing within the flow.
Southwest flow will slowly become more southerly at Palau as 96W and
the monsoon trough move northwest, with winds potentially becoming
variable at Yap as southwest flow weakens and then slowly becomes
more southeast.

NEAR EQUATORIAL TROUGH...
The near-equatorial trough (NET) is turning more into a broad surface
trough at it extends north-northwest from a buffer circulation near
the EQ148E, up into eastern Yap and western Chuuk State before
turning to the northeast and ending near 12N152E. Scattered showers
and isolated thunderstorms are developing along the eastern edge of
the trough, west and north of Chuuk Lagoon, and mainly over the outer
islands of Yap and Chuuk States, between 143E to 150E. This trough
will move northwest, pushing showers towards the Marinas and Yap
Proper over the next few days.

TRADE-WIND TROUGHS...
One trade-wind trough is located east of the Marianas, extending
from 10N151E to 22N155E, under the upper-level divergence associated
with the TUTT cell near the Marianas. Given the upper-level support
of the TUTT, scattered to numerous showers and isolated thunderstorms
extend along the trough axis. Hi-res models show this trough moving
into the Marianas this evening or tonight, helping to generate
scattered showers and isolated thunderstorms over the island chain.

There is a series of trade-wind troughs embedded within the ITCZ,
east of Majuro, from 175E and to the Date Line. Along these troughs,
scattered to numerous showers and isolated thunderstorms are
developing between 3N and 10N. As these troughs push westward,
shower and thunderstorm potential will increase across Majuro Atoll
and other islands in the vicinity Thursday, potentially pushing up
towards Wotje.

TUTT...
The TUTT enters the region 21N180, extending west-northwest to
25N162E before turning southwest and through the main TUTT cell
centered near 20N148E, just east of the Mariana Islands, then ending
near 5N144E. Currently, scattered showers and isolated thunderstorms
are observed near the TUTT cell and the trade-wind trough east of
150E. A couple of thunderstorms are developing to the west of Saipan
as the upper-level environment becomes more favorable for
thunderstorms to develop. The TUTT cell is expected to move across
the Marianas tonight, followed by the surface trough, supporting
scattered showers and isolated thunderstorms over the Mariana
Islands.

...ITCZ...
The ITCZ extends westward from 7N180 and ends west of Kosrae near
6N161E. Across the Marshall Islands and Kosrae, showers are fairly
spotty, but are increasing to between scattered and numerous east of
Majuro, near 175E to the Date Line, where a series of trade-wind
troughs are moving through the ITCZ. As the series of troughs
continue to move west, expect showers and the potential for
thunderstorms to increase the already wet pattern across the
Marshall Islands Thursday, to then follow at Kosrae and Pohnpei late
this week.

$$

Schank