073
AXPQ20 PGUM 200120
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1120 AM ChST Mon Jul 20 2026

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...
Numerous heavy showers and thunderstorms extend across much of
western Micronesia within a developing monsoon pattern, surging
across Palau and near Yap Proper. These showers and thunderstorms
have produced strong to near-gale gusts, and are expected to
continue across the area over the next few days as a broad
circulation begins to form nearby within the monsoon trough,
discussed in its own section below. Latest guidance shows the
disturbance developing to the north of Yap and Palau over the next
few days as the overall pattern shifts northwest, which could lead to
more intense showers, thunderstorms, and gusty winds over the islands.
This feature will dominate the weather pattern over far western
Micronesia for much of this week. For more information, please see
the latest Special Weather Statement for Palau and Yap issued by WFO
Guam.

...OTHER WEATHER SYSTEMS...

MONSOON TROUGH...
A broad monsoon trough extends across much of Micronesia, entering
the region near 10N130E where it stretches east-northeast, passing
to the north of Yap and Palau, south of the Marianas, then curving
east-southeast to extend north of Chuuk, Pohnpei, and Kosrae, before
crossing the Marshall Islands where it meets a weak surface
circulation near 5N174E. The trough then extends northeast toward
another weak circulation just east of the Date Line, exiting the
region at 9N180. Numerous heavy showers and thunderstorms extend
along and south of the monsoon trough axis over western Micronesia,
including over Yap and Palau. To the east, the trough is convectively
quiet, and most of the showers seen are associated with the two weak
circulations mentioned above, and an area of convergent westerlies
and northwesterlies seen over Pohnpei and Kosrae, which extend toward
a buffer circulation south of the trough axis. The portion of the
monsoon trough over western Micronesia looks to lift gradually north
to northwest over the next few days as a broad disturbance develops
within it, maintaining a very wet pattern over Yap and Palau. This
western portion of the trough will then break off from the broader
trough across central and eastern Micronesia, which looks to remain
fairly stationary over the next few days.

SURFACE TROUGHS...
A surface trough is seen west to north-northwest of Wake Island,
extending southwest into the region from 25N167E to 16N158E, from a
broad mid-latitude low-pressure system farther north of the region.
Isolated to scattered showers are seen along the trough axis. Model
guidance shows this trough gradually shifting west over the next few
days as it begins to interact with a remnant cold front or shearline
boundary, producing showers over the northern CNMI around midweek.

UPPER LEVEL TROUGHS...
A broad, weak, upper-level trough extends southwest into the region
from 25N150E, passing west of the Marianas and into far western
Micronesia to the west of Palau, near 7N133E. This upper trough is
interacting with a broad, convergent monsoon pattern over western
Micronesia to produce numerous heavy showers and thunderstorms across
Yap and Palau. This upper-level feature looks to shift west over the
next few days, exiting the region around midweek.

Another upper-level trough is seen to the east of the Marianas,
extending south-southeast from around 17N150E to near Chuuk at
7N152E. This trough will shift westward, and may help to support deep
convection within the developing monsoon pattern over western
Micronesia, around the middle to latter half of this week.

An upper-level trough is also seen over and northeast of the
Marshalls, extending southwest into the region from 18N180E, to south
of Majuro near 6N170E. This feature is interacting with a pair of
weak surface circulations in the area, to produce isolated
thunderstorms and scattered showers, east to northeast of Majuro, and
farther northeast across the Date Line. This upper-level trough will
shift westward across eastern and central Micronesia throughout the
week and may support showers and thunderstorms associated with the
monsoon trough and any transient weak surface features.

OTHER SYSTEMS...
A shearline boundary extends west-southwest into the region at
25N146E, connecting with the eastern periphery of a weak surface low
just west of Iwo To, near 25N140E. A line of heavy showers and
thunderstorms extends along this boundary. This feature looks to very
gradually drop south to southeast over the next few days with little
change in strength.

$$

DeCou