A typhoon is forecast during your trip and it's too late to postpone your travel or you're already there. What are some preparations and safety measures you can take?
Typhoons differ in intensity, but they're the most violent weather event on Earth and can be deadly. These steps are not all equally important, I just included the most information I could.
Japan being a mountainous island, it's particularly at risk for floods, surges and landslides. It is also one of the most disaster-prepared countries. Typhoon season in Japan is from September to November, the worst being until mid-October and mostly in Honshu in the south and southeast.
Before the typhoon hits
The safest place is away from rivers, canals and beaches (waves can surge several meters during the storm), away from cliffs and mountain slopes and anything that can fly into or fall on the house, so preferably in a tall building (big hotels have backup generators which is doubly useful) and not at the bottom of a slope. If not, on an elevated floor.
If you're staying in a house, check the drains and make sure there's no clogging. Remove pots or anything near windows that can be flown through them. Tape big X on windows to reduce shattering.
If you don't speak the local language, is there someone (either guest, host or staff) that can help you with communication?
Depending on how risky your location is, find the nearest shelter location. Ideally you want to move there before it gets bad. No one wants to lug their things outside during a violent storm, maybe at night, trying to find a place in an unfamiliar city.
If you're planning to drive, be aware that cars can hydroplane in heavy rain. If you're planning to train or fly away from the risk area do so in advance because flights/ferries will be cancelled before things get really bad and subways and train tracks can flood.
Usually typhoons last about a day or two. Get yourself some food for the time you'll be inside, especially water in case supply is interrupted.
If you need daily medicine, think to stock up for more than a couple of days, in case you're stuck.
Flashlights and batteries are also useful in case of a power outage.
Communication is very important so consider a portable battery charger (they're available at convenience stores) and use the internet from your phone. Keep your phone charged. Learn some local emergency numbers.
Keep a small bag of essentials ready in case you have to evacuate. This will happen quickly, you won't have time to find your things or pack a bag.
During the typhoon
Obvious, but stay inside. The risks during the typhoon include being swept off your feet by the winds, collision with debris carried by the wind, sudden floods and landslides.
Keep an eye on how fast water is accumulating outside. Water can rise very fast so you want to have the least surprise possible.
Keep informed. Watch or listen to local news, watch for alerts on how the situation is changing.
Keep someone in touch with your location. I believe Facebook has a "I'm safe" feature in case of natural disasters. Google maps has a "Share location" feature where you can send someone your exact location in real time for a given period of time.
Most important, if local officials issue an evacuation order, evacuate !
After the typhoon
Even after the storm blows over, some risk remains. Rivers will still be full or flooded so stay away from banks. The ground will still be full of water so stay away from mountain sides, hills or anywhere where the ground looks loose.
Some debris or branches that were stuck above and out of view can still fall suddenly.
If you can, avoid walking in stagnant water as they can carry water borne diseases.
Consider volunteering to help with recovery and cleanup. The elderly generally resist evacuation because it's difficult for them to move so it's useful to check if anybody is stuck in a flooded house and alerting local teams to them.
Japan Safe Travel Twitter (mostly English, but also Korean and Chinese)
Japan Shelter Guide app, iOS and Android
Pocket Shelter app
Safety tips app
Disaster Preparedness Tokyo
Shinjuku municipal website This is one ward in Tokyo, I'm sure other places have their own sites. This one is an automatic translation, it's also available in Thai, Korean, Chinese, French, Tagalog and Spanish among others. It also features a map of shelters in the ward.
NHK News (English)