Japan Travel Safety Kit · Guides

What do 'strong', 'very strong' and 'violent' typhoon mean in Japan?

JMA grades a typhoon by its maximum sustained wind: strong (33 m/s or more, under 44), very strong (44 or more, under 54) and violent (54 m/s or more). On JMA's maps the storm area is where winds of 25 m/s or more are blowing or may blow, and the strong-wind area is 15 m/s or more. If your city is inside the storm circle on the forecast, plan to be indoors for that window; trains and flights stop before it arrives.

Strength

JMA gradeMaximum sustained wind
Strong (tsuyoi)33 m/s or more, under 44 m/s (64 to under 85 knots)
Very strong (hijō ni tsuyoi)44 m/s or more, under 54 m/s (85 to under 105 knots)
Violent (mōretsu na)54 m/s or more (105 knots or more)

Size

JMA sizeRadius of winds of 15 m/s or more
Large500 km or more, under 800 km
Very large800 km or more

The two circles on the map

Storm area (bōfū-iki): winds of 25 m/s or more are blowing or may blow. Strong-wind area (kyōfū-iki): 15 m/s or more.

The one rule

Inside the storm circle, be indoors for that window. Japanese railways announce planned suspensions ahead of a typhoon and airlines cancel in the same window; check the evening before and book the extra night early.

The live warnings, in your language

Japan Disaster Guide is a free iPhone app that delivers JMA warnings for the places you save, after JMA confirms them, in 7 languages, with 115,000+ evacuation sites on a map.

Free on the App Store See the Japan Travel Safety Kit

The full procedures, the 119 script, shelter life, the 171 steps, 21 pointing cards and the worksheets are in the Japan Travel Safety Manual, a 66-page PDF made to read on a phone.

Get the manual ($9.99 PDF)
Sources (read 2026-09-09; quotations are verbatim)
  1. Japan Meteorological Agency, 台風の強さと大きさ (Japanese). https://www.jma.go.jp/jma/kishou/know/typhoon/1-3.html

Japan Disaster Guide is an independent app. It is not affiliated with the Japan Meteorological Agency or any government body. In an emergency, follow the instructions of local officials.

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