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Before You Go · Published 2026-09-29 · Updated 2026-09-29

Facts last checked 2026-09-29 · Next review 2027-04-01

Summer heat in Japan: what a "Heat Stroke Alert" means, and what to do

Japan's environment ministry and weather agency issue Heat Stroke Alerts when the WBGT heat index is forecast at 33 or higher. Here is how the alert works, where to check it, and the official advice.

A quiet sunny residential street under a blue sky
Photo: kazuyoshi sakamoto / Pexels

Japan runs an official alert for dangerous heat, and it is available in English. This article explains it, using the Ministry of the Environment (MoE) heat illness prevention site, checked on 2026-09-29.

What a Heat Stroke Alert is

From the MoE's English page:

  • A Heat Stroke Alert calls attention to dangerous heat and encourages people to act to prevent heat illness.
  • It is issued by the Ministry of the Environment and the Japan Meteorological Agency when the risk of heat illness is predicted to be extremely high, based on the WBGT heat stress index forecast.
  • Japan is divided into 58 regions, and the alert is announced by region.
  • It is announced when the WBGT index is 33 or higher.
  • It is announced at 17:00 the day before, and again at 5:00 on the day, based on the latest forecast.
  • The page also lists a separate Special Heat Stroke Alert.

The page describes the alert season as running from the fourth Wednesday of April to the fourth Wednesday of October. Its example dates are from 2021, so check the page for the current year's season.

A water bottle on blue stadium seats in the sun
Photo: Hassan Bouamoud / Pexels

What to do when an alert is issued

The MoE's advice when a Heat Stroke Alert is issued:

  • Avoid going out as much as possible, and keep your room cool with an air conditioner.
  • Avoid exercise as a general rule.
  • Check the heat index where you are, and act to prevent heat illness.
  • Children, older people, people with chronic illness and people with disabilities are more susceptible.
  • Drink before you get thirsty, take breaks at fixed times, and stay hydrated. The page gives 1.2 L per day as a guide.

What this means for sightseeing

  • Move outdoor sightseeing to the morning or evening on alert days, and plan indoor sights for midday.
  • Walking-heavy sights such as mountain temples, long stairways and big gardens are harder in the heat. Check the opening hours, since some close earlier than you might expect. See Opening-hours traps in Japan.
  • Carry water, and know where you can rest.

The Japan Tourism Agency's "Safety tips" app also sends heat stroke information in several languages. See Earthquakes, tsunami and typhoons in Japan.

If someone feels unwell

For an emergency, call 119 (ambulance). For medical help and hospitals that speak your language, see Getting sick in Japan as a visitor.

Sources