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TWDPQ 



Tropical Weather Discussion...UPDATED

National Weather Service Tiyan GU

1248 PM ChST Tue Sep 23 2025



Updated to include the recent issuance of a TCFA for 92W.



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 92W, centered NW of Yap near 10N136E, continues to show signs

of gradual organization. Latest scatterometry data show winds of

20-25 mph near 92W, mainly in the northern periphery. The JTWC has 

increased its development potential to HIGH with the issuance of a

Tropical Cyclone Formation Alert, meaning TC formation is likely

within 24hr. Widespread cloudiness, heavy showers and a few 

thunderstorms span the region from Palau and Yap northward to 15N 

from 133E to 140E. Westerly winds have been limited to 10-20 mph for 

both Yap and Palau with briefly stronger gusts, but heavy rains have 

made their presence known with Yap just reporting over 3 inches of 

rain the past 24hr. Invest 92W will continue to consolidate as it 

treks generally westward, though a number of models hint at a brief 

period of WSW motion between today and Wednesday. Primary concerns 

for the local region will be increasing winds and gusts, increasing 

potential for widespread heavy rains, and rising W swell and surf 

along S and W facing reefs. Winds, seas and surf could approach 

hazardous levels as early as tonight or Wed. For more information on 

92W, see bulletins issued by the JTWC under APBW10 PGTW and NWS Guam 

under WWPQ82 PGUM.



...OTHER WEATHER SYSTEMS...



MONSOON SURGE...

A westerly monsoon surge is seen just W of 130E and is flowing into

the developing 92W near Yap. This N-S oriented line of clouds and

heavy showers is trekking E at 20-25 kt. This surge, and similar

surges will move into western Micronesia waters in the coming days

resulting in quickly-changing choppy sea conditions and gusty winds. 



SURFACE TROUGHS...

A surface trough extends E from 92W to NW of Chuuk near 10N150E.

Showers and thunderstorms are found to the south, and to the north

within convergent SE flow heading into 92W, between 5N and 15N from

140E to 150E. This trough and attendant convection will steadily push

westward in tandem with 92W the next couple of days.



Another trough over the far NW Marshalls is combining with favorable

winds aloft to trigger scattered showers and thunderstorms over the

northern RMI atolls between 10N and 14N from 159E to 166E. As the

surface trough shifts west and weakens and the upper-level influence

wanes, showers and thunderstorms will diminish in the region. 



CIRCULATIONS...

A new circulation has formed within the surface trough that was N of

Wake Island 24hr ago. Heavy showers and thunderstorms are present NW

of Wake Island N of 20N between 162E and 166E. ASCAT data also

indicates winds of 25-35 mph in the eastern periphery of this

circulation. Models show little notable additional development of 

this circulation as it speeds to the NW and toward TY Neoguri

spinning near 31N153E.



UPPER-LEVEL LOWS...

Upper-level lows are found just SW of Wake Island near 18N166E and

west of the far northern CNMI near 21N139E. The first is aiding

convective development over the northern RMI, while the second has

aided development of convection west of the Marianas and north of

92W. The two upper lows will soon disconnect from their low-level

convective features, gradually reducing the coverage of showers and

thunderstorms.



OTHER SYSTEMS...



...ITCZ...

Showers and thunderstorms are developing along the ITCZ and stretch

eastward from Kosrae across Majuro to beyond the date line at 9N.

Majuro recently reported a little over an inch of rain the past 24hr.

Satellite imagery shows mainly scattered showers and a few 

thunderstorms with ASCAT data indicating winds of 10-15 mph. Model 

guidance continues to suggest this convective flare up will be short-

lived, likely decreasing by Wednesday evening as convergent E-SE 

winds become easterly and eases.



...LARGE NORTH SWELL...

TY Neoguri continues to spin up near 31N153E, well N of the AOR.

However, it has moved little and with its interaction with a nearby

cold front, the extent of a strong northerly wind has greatly

increased with a large region of 20-30 kt winds between Neoguri and

Japan with a smaller region of 30-70 kt winds closer to Neoguri.

These winds will continue to push large, long-period, N swell into 

the region in the coming days causing surf to rise to near hazardous

levels for many locations. 



$$



Aydlett