Tropical Storm Nari (#06W) – Tropical Cyclone Advisory #6: 1500 UTC 13 July 2025

…Nari strengthens as it rockets northward… …Forecast to pass just off the eastern coast of Honshu later today…

Current storm information:

• Position: 30.2°N 143.4°E

• Movement: N at 22 knots (35 km/h)

• Intensity: 50 knots (95 km/h)

• Central pressure: 994 hPa

Trend:

• Little change in strength is forecast during the next 24 hours.

Watches and warnings:

• Gale, thunderstorm, and high surf advisories are in effect for portions of the Kanto Plain and the southeastern coast of Honshu.

• Yokosuka Naval Base is under TCCOR Storm Watch.

Hazards affecting land:

• Interests along the eastern coast of Honshu and in the Aleutian Islands should monitor the progress of this system.

• U.S. military interests can get additional information from the Stars & Stripes Pacific Storm Tracker: https://www.stripes.com/theaters/asia_pacific/storm_tracker/

Discussion:

Nari is beginning to undergo some structural changes as it continues accelerating northward away from the Ogasawara Islands. The tropical storm has begun to interact with a mid- to upper-level low that has closed off over it, and its convection has started wrapping broadly around the surface center. There is a rather substantial tongue of dry air also wrapping into the circulation from the south and west, with signs of frontogenesis (the formation of cold and warm fronts) beginning to occur to the south, and the system as a whole is beginning to resemble an extratropical low rather than a tropical cyclone. Since the center is continuing to generate deep convection and still has a warm core, it is still a tropical cyclone for now. The intensity is increased to 50 kts, which is ahead of all the estimates and is based on an ASCAT pass from 1208 UTC that showed a large swath of 45 to 50 kt winds to the east of the center.

Nari is forecast to continue accelerating during the next 12 to 24 hours, as the system is caught up in strong southerly wind flow associated with an upper-level trough to the west and an unseasonably strong subtropical ridge to the east. Baroclinic influences and relatively warm SSTs could allow for a bit more strengthening today as Nari approaches Honshu. By late tonight, however, Nari will move over colder waters, and it should rapidly become a post-tropical cyclone as it turns northeastward near Hokkaido. The post-tropical cyclone should race eastward before exiting the basin near the Aleutian Islands on Thursday.

Forecast positions and maximum winds

• 00 hrs: 30.2°N 143.4°E – 50 kts

• 12 hrs: 34.4°N 142.6°E – 55 kts

• 24 hrs: 39.1°N 142.9°E – 50 kts Post-tropical/extratropical

• 48 hrs: 48.5°N 147.0°E – 40 kts Post-tropical/extratropical

• 72 hrs: 48.5°N 162.0°E – 30 kts Post-tropical/extratropical

• 96 hrs: 47.5°N 177.5°E – 35 kts Post-tropical/extratropical

• 120 hrs: 50.5°N 176.5°W – 35 kts Post-tropical/extratropical