Tropical Weather Discussion
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Tropical Weather Discussion
National Weather Service Tiyan GU
1038 AM ChST Wed Aug 20 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 90W remains disorganized and has been downgraded to "Low"
by JTWC, as it`s now located north of Koror near 11N135E. The
models show this feature remaining weak as it continues west, with
no real organizing, exiting Guam`s AOR by the weekend.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trough in the trades extends north from near Kapingamarangi to
just east of Chuuk, ending near 21N152E. Convection is widely
scattered along and ahead of this feature, which looks to be the
case as it continues west the next few days.

Another surface trough in the trades has strengthened more than
the models suggested it would, while also stretching both
southwest and northeast, which wasn`t anticipated. It now
stretches from southeast of Kosrae at 3N165E, to just east of
Majuro, to 10N175E. Scattered showers and isolated thunderstorms
are occurring along this feature, which looks to continue in the
latest model forecasts as it heads west the next several days.

Finally, a third trough is quickly following on the heels of the
Kosrae/Majuro trough. It`s a sharp but compact trough approaching
the Date Line. This feature will cross it tomorrow, bringing
additional convection to the region the next several days as it
continues west in the trade flow.

TUTT...
The TUTT has become more defined today and stretches from 25N180
westward to a cell northwest of Wake Island at 25N160E, then
extends southwest to 20N155E where another cell is trying to form,
continuing west to a cell west of the northern most part of the
CNMI at 20N140E. Most of the convection is associated near the
TUTT cells and to the south of the TUTT axis where better
divergence is present. The models do show the cell near 20N155E
developing, becoming a dominant feature by Friday, as it helps to
expand the TUTT westward to near 130E by the weekend while
maintaining a similar orientation.

...ITCZ...
A weak ITCZ stretched from south of Pohnpei to east of the Date
Line, centered between 4N and 10N. Widely scattered convection is
occurring with this feature, locally enhanced by surface troughs
in the trades. The ITCZ is forecast to expand westward and
gradually intensifies through the weekend, perhaps lifting
northward slightly as well.

$$

Doll