Environment JMA adopts ‘extreme heat day’ label for temperatures above 40°C

The JMA said on 17 April it has settled on a new term, "kokushobi", literally meaning "cruelly hot day", for days when temperatures reach 40°C or higher. The agency plans to add the term to its forecast language and start using it this summer. It said the move comes after a run of record heat in recent years, and is meant to make the danger clearer in simple terms.

At present, days of 25°C or more are referred to as "natsubi" (summer day). When temperatures hit 30°C, they are called "manatsubi" (midsummer day), and 35°C or above is "moshobi" (extremely hot day). There had been no specific term for 40°C or above. The JMA ran an online poll for a month, from late March, to find a name. "Kokushobi" drew 202,954 votes. That was roughly three times the total for the runner-up, "cho-moshobi" (super extremely hot day), and about eight times as many as "gokushobi" (drastically hot day), which placed next.

The Japan Weather Association, a general incorporated foundation, has independently used kokushobi since 2022 to refer to days of 40 °C or higher. According to the JMA, Japan has recorded days with temperatures of 40 °C or higher every year since 2018. On Aug. 5, 2025, Isesaki, Gunma Prefecture, recorded a temperature of 41.8 °C, the highest temperature ever observed in Japan.

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Health and weather authorities in Japan have struggled to get people to take extreme heat seriously. Last year, a record number of people suffered heat stroke as more cities logged their highest temperatures on record, despite repeated official warnings. So they decided to give the danger a name.

Earlier this year, the Japan Meteorological Agency held a public vote to choose a term for days when temperatures reach 40°C or higher, hoping it would encourage people to take extra precautions. The winning entry, receiving more than 40% of the vote, was kokushobi (酷暑日), or "cruel heat day".

The term was used for the first time on Tuesday after three cities in central Japan recorded temperatures of 40°C, the first such readings in the country this year. Officials urged people to stay indoors where possible, use air conditioning and drink plenty of water.

The agency's public poll in February and March garnered more than 400,000 votes, according to a statement. Kokushobi bested a dozen other terms that translate to "dangerously hot day," "sweaty day" and "sauna day." Mr. Kawasato said that meteorologists consulted with media and linguistics experts to form the list of names.

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Gifted by JREF:

My dog Daichi morning and evening walks have been changed to 6:00 a.m., before sunrise, and 7:00 p.m., after sunset. Every day, after walking the dog, I water the flower bed in front of our house and my mother's vegetable garden. Daichi loves getting sprayed with water from the hose, shaking his body happily and helping me water the plants.
During the day, the cat sleeps in the shade on the concrete by the front entrance. At night, it goes out hunting, and when I return from walking the dog, the cat comes to the doghouse and sneaks some of the dog's food.

Our morning inu sampou has shifted to 05:15 when humidity is crazy high, but temperatures are still tolerable. I wish Japan would change to Daylight Saving Time so our doggies could sleep at least until 06:00.

I hope you share a pic of your わんこ, @Hiroyuki Nagashima.

This is a photo of "Mint" the cat occupying "Daichi" the Border Collie's doghouse.



A cat stealing dog food.