Japan is set to begin this year's operation of its Special Heat Stroke Alert system Wednesday in an effort to reduce health risks from extreme summer heat.

The Environment Ministry will issue the special alert when dangerous heat levels are expected. Operation of the ordinary Heat Stroke Alert system covering days with possible heat-linked health risks will also begin the same day, and both systems will run through Oct. 22.

When the wet-bulb globe temperature (WBGT) index, which factors in temperature, humidity and sunlight, is forecast to exceed the threshold of 35 at all observation points in a prefecture, the ministry will issue the special alert at around 2 p.m. the day before.

While the special alert is in effect, municipalities will make air-conditioned facilities designated as cooling shelters open to the public. Organizers of school events and other activities will be asked to consider canceling or postponing them.

The ordinary alert system, operated by the Environment Ministry and the Japan Meteorological Agency, divides the country into 58 districts. The alert will be issued around 5 p.m. the previous day — or as late as 5 a.m. the day of — if the WBGT is forecast to stand at or above 33 at one or more observation points in a district.

The special system was established in 2024 and an alert has yet to be issued. The ordinary alert was issued a record 1,722 times last year.

"The special alert is information to prepare for when temperatures may exceed 40 degrees Celsius," a ministry official said. "We hope people will take caution following ordinary alerts, which mean it will be significantly hot."

Japan sweltered through its hottest summer ever in 2024, with record heat determined to be "almost impossible" without human-induced climate change.