Tropical Depression 21W (ex-Kiko) – Tropical Cyclone Advisory #3: 1200 UTC 3 September 2025

Subtropical depression transitions into Tropical Depression 21W as it continues northward.

Author

Will Weaver
September 03, 2025

…Subtropical depression transitions into Tropical Depression 21W as it continues northward…

Himawari-9 infrared satellite image (Weathernerds)

Current storm information:

  • Position: 27.2°N 131.6°E

  • Movement: N at 17 knots (30 km/h)

  • Intensity: 30 knots (55 km/h)

  • Central pressure: 1002 hPa

Trend:

  • Some slow strengthening is possible during the next 24 hours, and the depression could become a tropical storm later tonight or on Thursday.

Watches and warnings:

  • There are no land-based watches or warnings in effect.

Hazards affecting land:

  • Interests in Japan should monitor the progress of the depression. Heavy rain and gusty winds are possible in Kyushu beginning Thursday, before spreading over Shikoku and Honshu on Friday. U.S. military interests can get additional information from the Stars & Stripes Pacific Storm Tracker: https://www.stripes.com/theaters/asia_pacific/storm_tracker/ 

  • Interests in the Aleutian Islands should monitor the progress of this system.

Discussion:

The subtropical depression located east of Okinawa has gotten quite a bit better organized since the previous advisory. The depression now has a more classic tropical appearance, with convective banding wrapping fully around a much better defined circulation center. Although the system remains embedded underneath an upper-level trough, it now has a much less stretched appearance, and there are hints of a formative inner core on both satellite and radar imagery. Given these developments, along with scatterometer wind measurements of 25 to 30 kts and Dvorak fixes of T1.5 to T2.0, the system is now a tropical depression.

TD 21W remains embedded in southerly wind flow associated with an upper-level ridge to its east, and it is expected to continue on a northerly trajectory for another day or so. The environment is marginally favorable for strengthening with strong shear offsetting warm SSTs, but 21W is likely to become a tropical storm before it makes landfall in southern Kyushu late Thursday. After landfall, 21W should turn sharply east-northeastward as it rounds the northwestern periphery of the ridge. Although many of the ensembles (GFS, ECMWF, and Google DeepMind) and operational models show 21W continuing to the northeast and becoming an extratropical low, it appears more likely that 21W will be absorbed by another non-tropical low pressure system which is currently forming just to the east of Kyushu. Because of this, the forecast track ends after 48 hours, as this merger will likely happen late Friday as 21W moves off the eastern coast of Honshu.

Forecast positions and maximum winds

  • 00 hrs: 27.2°N 131.6°E – 30 kts

  • 12 hrs: 29.5°N 130.7°E – 35 kts

  • 24 hrs: 31.6°N 131.0°E – 35 kts inland

  • 48 hrs: 35.2°N 140.0°E – 35 kts inland

  • 72 hrs: Absorbed by extratropical low

JMA forecast map