The short answer
Earthquakes are sudden and typhoons are forecast, and the difference decides how you handle each. Japan runs an Earthquake Early Warning issued by the Japan Meteorological Agency when multiple seismometers detect a quake, along with official guidance on how to react. Typhoons come with days of notice: the UK FCDO puts the season between June and December, peaking between July and September, while Wikipedia's account of Japan's climate has five or six typhoons passing over or near the country every year from early August to early October. Save the numbers now: 119 for an ambulance, 110 for the police, and the Japan Visitor Hotline on +81 50 3816 2787 for English-language help during a natural disaster.
The Earthquake Early Warning, and what is behind it
Japan's Earthquake Early Warning is an alert issued when an earthquake is detected by multiple seismometers, primarily by the Japan Meteorological Agency, and it comes with official guidance on how to react. The network behind it is dense: the JMA runs 624 observation stations across Japan, set at intervals of about 20 km, in order to measure seismic intensity precisely. That density is what buys seconds between the first detection and the shaking arriving somewhere else. Whether a particular handset shows the alert depends on the phone and its settings, and we have found no source that lists which foreign phones do. So learn the response rather than relying on the phone to prompt you.
What to do in the seconds it buys
Follow the JMA's guidance and the instructions of the people around you, who have practised this since primary school. The general shape is simple. Indoors, get under a sturdy table or against an interior wall, away from windows, tall furniture and anything hanging, and stay there until the shaking stops. Do not run outside while the building is moving, because falling glass and signage are the common injury. On a train or in a station, hold on and wait for staff; services stop themselves and start again when they are checked. Outdoors, move away from walls, poles and overhangs. Afterwards, check your shoes are on, your phone is charged, and your accommodation's evacuation notice is read rather than skimmed.
Typhoons: when, and how to plan around one
Two windows are worth carrying in your head. The UK FCDO says the tropical cyclone season is between June and December, peaking between July and September. Wikipedia's article on the climate of Japan is narrower, with five or six typhoons passing over or near Japan every year from early August to early October. Use the wider FCDO window when you are picking dates and the narrower one to understand where the peak sits. A typhoon is a forecast event, so the useful habit is to check the Japan Meteorological Agency's warnings each morning of that season and to look at your own railway or airline's service information before you set off. We have no source describing how each operator handles a storm, so take that from them on the day.
The numbers to have before you need them
Three entries in your phone cover almost everything. 119 for an ambulance, which is also the number the fire service answers. 110 for the police. And the Japan Visitor Hotline, +81 50 3816 2787, which the UK FCDO gives as the line for emergency English-language assistance during natural disasters. Add your accommodation's address written in Japanese, a screenshot of your insurance policy number, and your embassy's local number while you are at it. Keep a power bank in your day bag through typhoon season, because a phone at eight per cent is the real emergency in a power cut. And keep your data plan active rather than relying on finding a network you can log into.
Keeping the phone useful
In both situations the phone is the thing that tells you whether the trains are running, where the nearest evacuation site is and that the people at home can stop worrying. That argues for landing already connected rather than hunting for a counter or a public network in the middle of a bad day. Goodbars sells a Japan eSIM you install at home and switch on when you land; it runs on NTT docomo, Japan's largest mobile network by mobile contracts, and our Japan coverage page shows where it reaches and what independent speed tests measure. Install it at home, keep a charged power bank with you, and download offline maps for the cities you are visiting before you need them. Then read your hotel's evacuation card on the first night rather than the worst one.
