Japan activates heatstroke alerts as early temperatures top 35 in multiple regions

Japan’s heatstroke alert system is back online

Japan’s heatstroke alert system runs from late April to Oct. 21, using the Wet Bulb Globe Temperature index instead of air temperature alone. A Heatstroke Alert starts at 33 or higher and a Special Heatstroke Alert kicks in at 35 or higher across a prefecture.

The system was activated for 2026 in late April after early temperatures topped 35°C in multiple regions. No alerts are currently in effect nationwide and WBGT levels were below alert thresholds on May 7.

What it means for nomads and travelers

The alerts matter most for expats, digital nomads and tourists in humid heat, especially in places like Kanto, Tokai and Okinawa. WBGT factors in temperature, humidity, solar radiation and wind, so it can be more useful than the number on a weather app.

Japan’s official guidance says to use air conditioning, drink water and salt and avoid outdoor exertion. Exercise should be limited at 28 WBGT and stopped entirely at 31.

How to check alerts and stay ahead of them

The alerts are public and don’t require registration or fees. Travelers can check daily maps and forecasts online or sign up for email updates, including Japanese-language notices, through official channels and /visa updates resources.

If WBGT reaches alert levels, cooling shelters may open and events can be canceled at the prefecture level. Read our full Japan guide for the complete picture.