Japan Heatwave: Which Cities are Under Heatstroke Alerts

Japan is in general heatstroke alert as several regions experience higher temperatures of more than 40 degrees Celsius during the heatwave, straining the country’s emergency services and sending warnings of life-threatening situations. The Japan Meteorological Agency (JMA) has issued heatstroke warnings for 41 of the 47 prefectures in Japan.

At least 14 people died from heat-related illnesses in the past week while nearly 11,000 more were treated at the emergency room in the same time frame, emergency officials said. Hospitals and first responders are also under pressure due to the extreme heat.

On July 23 alone, the Tokyo Fire Department reported 453 people with heat-related illnesses were sent to hospital, up from the previous year’s high of 335, and the highest since records began in 2010.

The department also had its highest number of emergency callouts since at least 1963. About 14 million people live in Tokyo, where one person has died, and four others are in critical condition and 18 in serious condition during the current heat wave.

Which Cities Are Under Heatstroke Alerts?

The Japanese Meteorological Agency has sent heatstroke warnings to Japan’s residents, with a specific call to older people to drink water and avoid excessive outdoor activity and use air conditioning if available.

At least 6 places reached temperatures of 40°C or more by early afternoon on July 24th. The hottest places in the country were Hamamatsu in Shizuoka Prefecture at 41.1 degrees Celsius, Toyota in Aichi Prefecture at 40.8 degrees Celsius, and Kuwana in Mie Prefecture at 40.7 degrees.

Forecast temperatures reached over 36°C in Tokyo earlier in the week. The JMA recorded the high temperatures of 37 degrees Celsius at Nagano and 38 degrees Celsius at Nagoya, Kumagaya and Kofu. Nagoya later hit 40℃, its first kokushobi day of 2026.

The heatwave has also killed people in the countryside out of town. An 85-year-old died inside a greenhouse at his farm in Tochigi Prefecture, north of Tokyo, local media reported.

What is Kokushobi, Japan’s New Heat Category?

The JMA introduced the term kokushobi on April 17, 2026, to describe any day when the maximum temperature reaches or exceeds 40 degrees Celsius. The term uses the kanji for “harsh” or “cruel.”

The highest heat classification in Japan before was moshobi, for days when temperatures reached at least 35 degrees Celsius. The new designation doesn’t automatically lead to more government action, but it was created to “grow public awareness to the increasingly dangerous heat.

The heatstroke alert system is based on the Wet-bulb Globe Temperature (WBGT), which takes into account the air temperature, humidity, radiant heat, and wind speed to measure the heat stress instead of only the air temperature.

What Authorities are Saying

The JMA is warning that the dangerous conditions are likely to continue.

“Temperatures have been rising since mid-July, and severe heat is expected to continue nationwide,” the agency said. “It is no exaggeration to call this extreme heat a ‘disaster’ with many people being rushed to hospitals or even dying as a result of heatstroke.”

A Tokyo Fire Department spokesman has also advised residents to be alert.

“We are urging people to stay hydrated and use air conditioners,” the spokesperson told AFP, adding that the number of heat-related patients increased as temperatures climbed, particularly on July 22 and July 23.

A Pattern of Increasingly Extreme Summers

In recent years Japan has seen an increase in the severity of summer heat. The Fire and Disaster Management Agency said that 4,580 individuals were admitted to hospital due to heatstroke from July 6 to July 12, with seven of these patients succumbing to the condition. During the 2025 summer, over 100,000 people were admitted to hospitals for heatstroke.

The highest temperature ever recorded in Japan was 41.8 degrees Celsius on Aug. 5, 2025, in the city of Isesaki. Human-induced climate change has been linked to the rise in frequency and severity of extreme heat events in Japan.

The Japan Meteorological Agency (JMA) forecast that it will keep experiencing severe heat conditions nationwide in the next few days and reminded people to pay attention to official forecasts and take measures to prevent heat-related illnesses.