Start of Operation for the 2025 Heat Stroke Alert

The Ministry of the Environment and the Japan Meteorological Agency have started the operation of the "Heatstroke Alert" for the fiscal year 2025 from Wednesday, April 23, 2025.

• Heat Stroke Warning Alert (Japan Meteorological Agency Press Release)(External Link)
• Heat Stroke Special Warning Alert (Ministry of the Environment Press Release)(External Link)

Background and Purpose

In recent years, the number of emergency transports and deaths due to heatstroke has remained at a high level, so the Ministry of the Environment and the Japan Meteorological Agency have been operating the "Heatstroke Warning Alert" nationwide since fiscal year 2021.
The "Heat Stroke Warning Alert" is information based on the Wet Bulb Globe Temperature (WBGT) index, issued when an extremely high risk of heat stroke is predicted due to hot environmental conditions. It aims to raise awareness of heat exposure and effectively encourage the public to take preventive actions against heat stroke.
Operation will continue to start nationwide in fiscal year 2025 as well.
Starting from the fiscal year 2024, a "Heat Stroke Special Alert" will be issued in cases where there is a significant risk of serious health damage due to particularly high temperatures.
Note: The Heat Index (WBGT) is an indicator of the risk of heatstroke, composed of temperature, humidity, radiant heat (such as sunlight), wind, and other factors.

Overview

• About "Heat Stroke Warning Alert" and "Special Heat Stroke Warning Alert" (Source: Ministry of the Environment) (PDF 103.0KB)

Presentation Unit

Heat Stroke Warning Alert: Announced based on prefectural forecast districts divided into 58 nationwide units
Heat Stroke Special Warning Alert: Prefecture Level

Announcement Criteria

Heat Stroke Alert: Issued when the daily maximum heat index (WBGT) is predicted to be 33 or higher at any of the calculation points within the target area.
Heat Stroke Special Warning Alert: Issued when the maximum heat index (WBGT) for the next day is forecasted to be 35 or higher at all heat index information provision points within each prefecture.

Announcement Timing

Heat Stroke Alert: Announced based on the latest forecast values at 5 PM the previous day and 5 AM on the day
Heat Stroke Special Warning Alert: 2 PM the Previous Day

Period

From 5:00 PM on Wednesday, April 23, 2025,to the announcement at 5:00 AM on Wednesday, October 22, 2025

Details

For more details, please refer to the Ministry of the Environment's Heatstroke Prevention Information Site or the Japan Meteorological Agency's website.

• Ministry of the Environment Heat Stroke Prevention Information Site(External Link)
• Japan Meteorological Agency Website(External Link)

Heat Stroke Prevention Actions at the Time of Announcement

Examples of Preventive Actions

• Avoid non-essential outings and use air conditioning regardless of day or night
• Encourage those around people at high risk of heatstroke (Older Adults, children, etc.) to check on them
• Check the local heat index (WBGT) and use it as a guideline for your actions
• Exercise indoors or outdoors without air conditioning, etc., should in principle be canceled or postponed.
• Practice more than usual heatstroke prevention measures, such as frequently hydrating before you feel thirsty.

How to Confirm Information

To check the Heat Stroke Alert, please use services such as the "Personal Email Delivery Service" and the "Ministry of the Environment Official LINE Account".
Note: Please check the Ministry of the Environment's Heat Stroke Prevention Information Site for registration methods.

• Heat Stroke Warning Alert Preventive Actions When Announced (Source: Ministry of the Environment) (PDF 820.4KB)