655
AXPQ20 PGUM 050043
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1043 AM ChST Sat Jul 5 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...

MONSOON TROUGH...
A weakening southwesterly monsoon flow extends from between 12N
and 18N at 130E to the northeast, becoming more southerly near
22N150E, with slight veering/backing ~150 miles to either side of
this meridian. No significant convection is found until you get
near Pagan in the CNMI, where infra-red satellite imagery has a
convective signature of a mature MCC with very good poleward
outflow from the southern through western flanks, aided by the
upper-level flow. Continuing north, convection is located in an
arcing (almost like an occluded front) to the east of an axis that
bends westward to an Asymmetric weakening tropical storm located
well to the east of southern Japan.

TRADE-WIND TROUGHS...
The first in a series of surface troughs in the trade flow
centered between Majuro and the Date Line. Here, decent convective
coverage with cloud tops occasionally pushing -75 deg.C is noted
on the infra-red satellite imagery loop. Convection is getting a
boost ascent-wise as it`s sandwiched between a TUTT cell to the
north and an upper-level high to the east of Majuro. This storm-
top ventilation is allowing for widespread cloud cover and showers
to continue, with the occasional thunderstorm mixed in as well.

Heading west, the next trough bisects Majuro and Kosrae. This
feature is fairly pronounced in the latest streamline analysis
(model), but, very little convection has been observed with just
recent attempts of convection development over a more
"significant" area noted east of Kosrae.

The third and final trough extends from EQ145E to near eastern Yap
State at 6N145E where it intersects a col, before continuing
northward through the spine of Guam and the CNMI to near Pagan,
before becoming northeast slightly, then gradually back to the
northwest near 25N as it continues to a weakening tropical storm
well east of the southern tip of Japan.

The first two troughs mentioned above will continue westward, with
the surface wind flow south of 10N and west of 145E modulated by
the trough axis and col. As the Meridional trough near 145E
begins to feel the effects of the approaching Kosrae trough, the
models show some semblance of a weak circulation developing
southwest of Chuuk by 6Z July 7th. It remains disorganized as it
continues west in a weak form, as does the Majuro trough
(continues to move westward). The wind flow will be dictated by
whether this weak circulation forms or not, but, seasonably-high
PWATs and weak shear should allow convection to become more
widespread near any weak circulation that may develop.

Light winds near Guam and the southern half of the CNMI along with
respectable surface convergence and moisture quality/depth will
allow for episodic convection to continue to develop, aided by
orographics during daytime heating along the southern and western
sides of the islands, and nocturnally at night for the next
several days.

Finally, given good moisture quality and weak shear, the Majuro
trough will stay convectively-active despite outrunning the
divergence aloft currently situated over it, as it affects the
remainder of Eastern Micronesia over the next few days.

TUTT...
An upper-level low is located just outside of Guam`s AOR at
27N180. extending west-southwest is a TUTT axis that turns more
southwesterly northeast of Wake Island at 25.0N 171.6E, extending
southwest as it bypasses Wake Island ~100 miles to its east, with
this TUTT axis continuing southwest before ending south of Chuuk
at 4.3N 151E. Divergence aloft between this and an upper low, and
an upper-level high due east of Majuro along the Date Line is
helping foster decent convective coverage across much of the RMI.

...ITCZ...
The fragmented ITCZ mentioned yesterday is no longer apparent with
relevant convection tied to surface troughs in the trade flow, as
mentioned above.

$$

Doll