Japan's Heat Stroke Alert: what it is and what to do in summer
Japan has an official Heat Stroke Alert, issued when heat illness risk is extremely high. It runs from late April to late October. When one is issued, avoid going out if you can, stay cool and drink water.
What the alert is
The Ministry of the Environment and the Japan Meteorological Agency (JMA) issue a Heat Stroke Alert when the risk of heat illness is predicted to be extremely high. It is based on a heat index called WBGT, which includes temperature, humidity and sunlight.
- The alert is issued when WBGT is forecast to be 33 or higher.
- Japan is divided into 58 regions, and alerts are announced for each region.
- Alerts are announced at 5:00 pm the day before and again at 5:00 am on the day.
When it runs
The alert system runs from the fourth Wednesday of April to the fourth Wednesday of October. The 2026 season ended on October 21, 2026, so you will not see alerts in winter.
What to do when an alert is issued
- Avoid going out when you can, and keep your room cool with air conditioning.
- Generally avoid exercise.
- Take breaks often, and drink water before you feel thirsty.
- Take extra care of children, older people and people with health conditions.
Planning your day in summer
- Put outdoor sightseeing in the morning, and plan indoor places such as museums, department stores or cafes for the afternoon.
- Increase activity slowly. The Ministry says to avoid overexertion and to get used to the heat gradually.
- Be careful even when no alert is out. The Ministry says heat illness can happen when WBGT is lower, depending on where you are, how you feel and what you are doing.
How to check
The Ministry of the Environment's English website shows alerts for today and tomorrow, and the current WBGT. It also has a first aid checklist for heat illness. If someone is seriously unwell, see our emergency page for how to call for help.
FAQ
Is there an English page for the alert?
Yes. The Ministry of the Environment runs an English site called Heat Illness Prevention Information.
Does no alert mean it is safe?
No. The Ministry notes that heat illness can happen even when the index is lower, depending on the place and your condition.
What should I do if I feel very unwell in the heat?
Move to a cool place and ask for help. In an emergency, call 119 for an ambulance. See our emergency page.
Sources
Related tips
- Emergency numbers in Japan: 110, 119 and the visitor hotlineWho to call in Japan: 110 for the police, 119 for an ambulance or fire, and a 24-hour English hotline for visitors.
- If you feel sick in Japan: how to find a clinic that helps foreign visitorsCall the Japan Visitor Hotline (050-3816-2787, 24 hours) or use the JNTO list of medical institutions that accept foreign visitors. Medical costs can be very high, so travel insurance is strongly recommended.
- Typhoons and heavy rain in Japan: how to read the warning levelsJapan Meteorological Agency (JMA) uses warning levels from 1 to 5. At Level 3 people who need more time should start to evacuate, at Level 4 everyone in the danger area should evacuate, and Level 5 is an emergency.
- Safety tips: the disaster alert app for visitors to JapanSafety tips is an app supervised by the Japan Tourism Agency. It sends push alerts for earthquakes, tsunami and severe weather, in 15 languages.
Last checked: 2026-11-01. Rules and prices can change, so please confirm with the official sources above.