813
AXPQ20 PGUM 180101
TWDPQ

Tropical Weather Discussion
National Weather Service Tiyan GU
1101 AM ChST Mon Aug 18 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 continues to remain rated as "sub-low" by the JTWC.
Abundant cloud cover makes it difficult to tell if a low-level
circulation center is trying to form, and we`re awaiting the
latest scatterometer pass to aid in this analysis. That said, the
new ECENS went "gonzo" (really shows) a rapidly-developing LLCC as
it heads west-northwest, passing south of Guam. In general, the
GEFS shows a similar track but doen`t develop a LLCC for another
24 hours, and when it does so it`s south of Guam along a track
"error cone" that matches up with the ECENS nicely. We suspect the
GEFS is "late to the game" and is attempting to "play catch up"
given the amount of persistent convection near 90W. Either way, a
developing circulation looks to be in the cards as it enters the
Philippine Sea with questions remaining with regard to strength
and to some extent timing.

The convection associated with a monsoon-like trough mentioned
yesterday has moved west, out of Guam`s AOR.

...OTHER WEATHER SYSTEMS...

TRADE-WIND TROUGHS...
A trade-wind trough stretches from Koror northeast to near the
northern tip of the CNMI at 21N146E. Most of the convection with
this feature is found from near Koror to 15N139E, generally along
and ahead of the trough. That said, MIMIC water vapor imagery
shows only a slight drop off in PWATs and would expect at least
scattered convective coverage, locally higher, as this feature
continues west the next few days.

The next trough in the trades is located from well south of
central Yap State near 5N145E northeast through western Chuuk
State as it intersects 90W at 8.9N 151.8E, with the trough
continuing to 13N152E. Widespread cloud cover, showers, and a few
thunderstorms are occurring. The models show the trough
continuing westward and possibly extending further north/south as
90W develops. Significant disagreement exists with how fast a LLCC
develops with 90W, making for a "low confidence forecast" in
terms of trough positioning and the strength of the wind fields as
a tropical cyclone eventually develops. In general, a further
increase in convective coverage and intensity seems probable over
the next few days.

Finally, a trough in the trades extends from near Kwajalein
northeast to near 14N174E. Very little convection is occurring
with this feature currently, but MIMIC imagery shows PWATs
increase from ~1.6 inches to over 2 inches, with the models
showing increasing convective coverage the next few days as it
continues its westward journey.

TUTT...
A TUTT enters Guam`s AOR north of Wake Island at 25N165E to a
TUTT cell west of Wake Island at 20N170E before exiting Guam`s AOR
at 25N144E. The models show this feature flattening and lifting
north somewhat in the next 2 to 3 days.

...ITCZ...
The ITCZ has mainly dissolved with any relevant convection tied to
surface troughs in the trade flow. With that said, the models show
a redevelopment of this feature mid week. It remains unclear how
long the redeveloped ITCZ maintains integrity though. Stay tuned.

$$

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