Tropical Depression #18W – Tropical Cyclone Advisory #6: 1200 UTC 20 August 2025

Tropical Depression 18W passing west of Kagoshima, could still briefly become a tropical storm before dissipating by the end of the week.

Author

Will Weaver
August 20, 2025

…Tropical Depression 18W passing west of Kagoshima… …Could still briefly become a tropical storm before dissipating by the end of the week…

Himawari-9 infrared satellite image (Weathernerds)

Current storm information:

  • Position: 31.1°N 128.2°E

  • Movement: NNE at 10 knots (20 km/h)

  • Intensity: 30 knots (55 km/h)

  • Central pressure: 1005 hPa

Trend:

  • Little change in strength is forecast during the next 24 hours, although the depression could very briefly become a tropical storm on Thursday.

Watches and warnings:

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

Hazards affecting land:

  • The depression is likely to produce heavy rainfall in portions of Kyushu beginning on Thursday and continuing through the weekend. This rain could result in flash flooding. For additional information, refer to products from your local weather office. U.S. military interests can find additional information at the Stars & Stripes Pacific Storm Tracker: https://www.stripes.com/theaters/asia_pacific/storm_tracker/

Discussion:

Radar data from Kagoshima in Kyushu, Japan suggests that the circulation of Tropical Depression 18W has become a bit better defined since the previous advisory. Although the convection remains somewhat formless with little in the way of banding features, it has increased in coverage, with fragments of a band wrapping into the very compact circulation center. Scatterometer data indicates that the depression continues to produce a rather wide swath of 25 to 30 kt winds primarily to the east of the center. These observations, combined with Dvorak fixes ranging from T1.5 to T2.0 from the various agencies, result in the intensity remaining 30 kts. 

TD 18W is currently in a marginally favorable environment. Although shear is quite low (5 to 10 kts) and SSTs are actually unusually warm for where it is, these are offset by a relatively dry air mass surrounding the depression. Still, given 18W’s compactness, it is possible that it could strengthen a little during the next 12 to 24 hours or so and briefly become a tropical storm as it gradually turns northeastward under the influence of a ridge centered to the southeast. By late Thursday evening, however, a strong ridge is expected to move into the Sea of Japan, which will dramatically increase easterly shear over 18W. Combined with 18W moving inland over northern Kyushu, this shear will make very quick work of 18W’s small circulation, and the system will likely dissipate outright by Friday evening.

Forecast positions and maximum winds

  • 00 hrs: 31.1°N 128.2°E – 30 kts

  • 12 hrs: 32.3°N 128.4°E – 35 kts

  • 24 hrs: 33.0°N 129.2°E – 30 kts inland

  • 48 hrs: 33.5°N 130.6°E – 25 kts inland

  • 72 hrs: Dissipated

Forecast map