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AXPQ20 PGUM 010106
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1106 AM ChST Mon Sep 1 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...
Yesterday`s monsoon trough has lifted north and west and now extends
from 16N130E to 21N141E. To it`s south, southwesterly to southerly
winds in the monsoon flow associated with Invest 95W are leading to
fairly widespread convection north and west of a Koror to Yap
line. These features will continue to lift north and west as both
disturbances continue to slowly pull away from Guam`s AOR over
the next several days.

TRADE-WIND TROUGHS...
The long surface trough near Chuuk yesterday continues it`s
westward journey, now stretching from EQ151E to Onoun in western
Chuuk State, continuing to 19N149E, which is east of Saipan.
Widely-scattered showers continue to develop along the trough from
the equator to 14N, becoming locally widespread between 14N and 19N
from 149E to 151E, where surface convergence is getting a boost of
ascent from the tail of a TUTT that has sagged south, helping to fuel
the convection. This trough is anticipated to continue west the next
several days with scattered convection along it.

Farther east, another trough stretches from west of Nukuoro
through eastern Pohnpei, through Ujae and Utirik in the FSM,
ending near 14N174E. This feature denotes the axis of greatest
moisture concentration per MIMIC water vapor imager, with PWATs
of 2.4 to 2.8 inches common. This also denotes a temporarily
weakening ITCZ, which is discussed in the section below. Look for
this trough to continue west the next several days, potentially
becoming more convectively-active for the latter half of the week
as it approaches Chuuk and the Marianas.

TUTT...
Today the TUTT enters Guam`s AOR at 25N171E, continuing southwest
and then west to east of the CNMI at 20N150E, where a broad cell
is trying to form. The TUTT axis then lifts northwest to a col at
24N144E, before continuing west and exiting the area at 24N130E.
To it`s south is a pair of upper-level highs, centered at 15N180
and west of the 18N135E, with a ridge axis passing through a col
at 13N160E.

Modest to moderate divergence is found along the southern TUTT
axis. Convection is in greater concentration along this southern
axis and near the TUTT cells. The astern upper high cell has
scattered convection along it`s southern half of the circulation,
and west of Guam and the CNMI where very good divergence is found,
as this is more of an inflection point trying to develop into an
area of high pressure.

The models show the TUTT will reorientate this week with a cell
north of Wake Island near 23N175E and a TUTT "tail"/axis extending
to near Guam and the CNMI where it`ll end, as the developing area
of high pressure west of the Marianas strengthens and repositions
west-northwest.

...ITCZ...
The ITCZ is found south of a line from west of Nukuoro, through
eastern Pohnpei, continuing through Ujae (9N 165E) and Utirik
(11N170E) respectively, in the FSM and ending northeast of there.
Trade convergence is found along this feature as is increased
moisture, typical of an ITCZ. However, todays runs show this feature
will continue to weaken over the next 48 hours as it slowly continues
west. Then, a new and more "traditionally-aligned" east-west ITCZ
fragment crosses the Date Line between 4N and 9N, as it catches up to
the previous fragment (just mentioned) by late Thursday, helping to
energize it as it expands westward. By Saturday, another fragment
again surges across the Date Line between 4N and 10N. In short,
bursts of convective activity will continue to occur through he
weekend near any fragment or surface trough interacting with the
fragments.

$$

Doll