267
AXPQ20 PGUM 290144
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1144 AM ChST Tue Jul 29 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 CYCLONES AND MONSOON SURGE...
The monsoon trough is located mainly north of Guam`s Area of
Responsibility (AOR), linking TS Co-may, located northeast of Taiwan
near 27N125E, and TS Krosa, located north-northeast of Iwo To near
28N143E. The monsoon trough dips south into the AOR between these
tropical systems, with its southernmost point located near 23N136E.
Although TS Krosa and TS Co-may are located well north of the AOR,
their effects are felt within the region.

South of the monsoon trough, the overnight scatterometry reveals a
broad area of strong to near-gale southwest winds, extending from
beyond 130E to roughly 145E, and from 15N to 20N. A band of
convergence along the leading edge of this strong monsoon flow is
generating numerous showers and scattered thunderstorms west-
northwest of the Marianas, supported by strong upper-level westerlies
which are enhancing divergence aloft. To the northeast, a secondary
band of scattered to numerous showers and isolated thunderstorms is
seen feeding directly into TS Krosa, extending along the southern
portion of the monsoon trough just south of Iwo To toward
Minamitorishima. Latest altimetry data in the region show elevated
seas of 10 to 15 ft associated with the broad monsoon surge, from
around 138E to 146E and 19N to 23N, with some data points suggesting
hazardous seas exceeding 15 ft may be felt within this area north of
the CNMI.

Model guidance indicates that fresh to strong monsoon flow and
elevated seas will continue for much of the week, within the region
to the west and north of the Marianas. As Krosa lingers to the north
of Iwo To, the strongest winds look to gradually narrow in areal
extent and weaken through end of the week, while seas gradually
relax as well.

For more information on TS Krosa and TS Co-may please refer to
bulletins from the Joint Typhoon Warning Center under WMO header
WTPN31 PGTW and WTPN33 PGTW, respectively.

...OTHER WEATHER SYSTEMS...

TRADE-WIND AND SURFACE TROUGHS...
A series of trade wind troughs is seen across the region extending
east from north of Chuuk State through eastern Micronesia. A robust
surface trough is seen to the north of Chuuk Lagoon with its axis
roughly oriented east to west, along 150E from 10-12N. Model
streamlines and CIMSS 850-700 mb vorticity imply some low to mid-
level cyclonic rotation here, but this isn`t well seen in the latest
visible satellite loop. Scattered to numerous showers are seen within
this trough. To the east, a robust southwest to northeast-oriented
trough is seen within the ITCZ to the northeast of Pohnpei, with
scattered to numerous showers along the axis. Several more such
troughs are seen within the ITCZ further east, over the northern RMI
passing over Kwajalein, and to the east of Majuro extending northeast
to the Date Line. Scattered to numerous showers are seen across the
region covering much of the RMI, with isolated thunderstorms seen
south of Majuro and northeast of the RMI. The trough north of Chuuk
looks to shift northwest with little development and weaken over the
next few days. The troughs across eastern Micronesia look to shift
west along with the ITCZ over the next few days, increasing showers
mainly near Majuro, Pohnpei, and Chuuk.

TUTT...
The TUTT extends north-northeast from 13N171E through a TUTT low
centered east of Wake Island near 22N176E, continuing north-northeast
through 25N178E. Scattered showers and patchy clouds are seen near
Wake, with scattered showers and isolated thunderstorms seen
northeast of the Marshall Islands along the southern edge of the TUTT
low where there is a weak trough at the surface. The TUTT will remain
quasi-stationary through the week as it extends further southwest
across Wake Island to the north of Chuuk and Pohnpei States.

OTHER SYSTEMS...

...ITCZ...
The ITCZ extends west-northwest into the region near 5N180, across
the Marshall Islands passing near Majuro and Kwajalein, then curves
west across northern Pohnpei State to around 10N155E. Scattered to
numerous showers, isolated thunderstorms, and extensive cloudiness
are seen along the ITCZ, particularly where there are trade-wind
troughs intersecting. Convection is mainly focused over and east of
Majuro, west to northwest of Kwajalein, and north-northeast of
Pohnpei. A weaker band of convergence is seen further south,
extending west of the southern RMI, passing to the south of Kosrae,
Pohnpei, and Chuuk Lagoon. Patchy showers and clouds extend across
this weak convergence band as well. The ITCZ looks to become more
fragmented over the next few days as a series of trade-wind troughs
across eastern and central Micronesia, then organize once more by the
weekend.

LOW-LEVEL RIDGE...
A broad low-level ridge extends across the region from 25N165E,
passing south of the Marianas and continuing just south of Yap and
Palau in far western Micronesia. Within the ridge, drier conditions
prevail over and east of the Marianas, and near and southwest of
Palau, but embedded troughing and convergence is generating scattered
showers across much of Yap State east of Yap Proper. This ridging
pattern looks to continue for much of the week.

$$

DeCou