371
AXPQ20 PGUM 170112
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1112 AM ChST Fri Oct 17 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...
Invest 96W from JTWC has been upgraded to a medium rating,
meaning tropical cyclone development is likely but beyond 24
hours. The center of the circulation in located near 13N130E,
moving out of Guam`s AOR. Robust convection continues to develop
along its northern through eastern flanks, as the system remains
asymmetric due to moderate upper-level wind shear. This
discussion will be the last mention of 96W in the tropical
discussion.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trade-wind trough stretches from southeast of Eauripik at 5N145E
through Polowat in western Chuuk State before ending northeast of
there at 11N156E. Most of the convection, in the form of scattered
showers and isolated thunderstorms is found from just south of
Polowat along this trough, to near Polowat and Chuuk. Convection
then becomes numerous showers with isolated thunderstorms from 10N
and points northward along the trough axis due to increased
divergence aloft/stronger TUTT interaction.

The models show this trough becoming somewhat less convectively-
active as it heads west the next few days as it loses the upper-
level divergence/TUTT support. However, at least widely-scattered
showers with a few thunderstorms continuing seems probable.

TUTT...
The mid-latitude trough that was mentioned yesterday has
transitioned into a TUTT with one cell developing northwest of
Wake Island near 22N162E with the TUTT axis extending southwest to
another developing cell near 15N157E, with the axis continuing
south-southwest before ending southeast of Chuuk near 6N156E.
Scattered convection is developing near the periphery of the Wake
Island cell. Farther southwest, the northern hall of this cell is
largely void of convection with MIMIC water vapor imagery showing
a pocket of dry air west of Wake Island extending southwest into
the northern half of the cell near 15N157E. Along its (the
southern cell) southern half of the circulation, numerous showers
and scattered thunderstorms are occurring due to much higher PWATs
and divergence aloft aiding updraft intensity. Convection then
decreases to scattered showers and isolated thunderstorms along
the remainder of the TUTT axis (between 6N and 10N).

Looking ahead, the southern cells is forecast to drop further
south to near Chuuk (GFS) or Pohnpei (ECMWF) during the next 36
hours, with the Wake Island cell lifting northeast. this
stretches/elongates the TUTT with the axis reaching the equator
along its southern pint during the next 48 to 60 hours. This
should aloft for deeper moisture entrainment along at least the
southern half of the TUTT with potentially more vigorous
convection developing over the next few days.

$$

Doll