By Japan reveals new name for 40C-and-hotter days after blistering summer
New Official Term for Extreme Heat
Japan has introduced a new official name for days when temperatures reach 40C or higher. The term kokushobi was chosen following a national survey and has been translated as cruelly hot day, brutally hot day, or severely hot day. The Japan Meteorological Agency officially adopted the description after the country experienced its hottest summer on record in 2025.
The word uses koku which means harsh or cruel combined with elements describing extreme heat. This addition completes a set of official heat categories that already exist for days exceeding 25C, 30C and 35C. The new term reflects growing concern over increasingly intense heatwaves across the country.
Survey That Selected the Name
The Japan Meteorological Agency conducted an online survey between February and March that received roughly 478,000 responses. Participants chose from 13 different options to describe the hottest category of days. Kokushobi emerged as the clear favourite with super extremely hot day finishing in second place.
The agency introduced the new term on Friday as part of efforts to communicate extreme weather risks more effectively to the public. The decision comes after record-breaking temperatures affected many parts of Japan during the previous summer.
Record-Breaking Summer of 2025
Summer 2025 was the hottest since records began in 1898 with nationwide average temperatures 2.36C above the long-term average. Temperatures reached 40C or higher on nine separate days between June and August. The highest temperature recorded was 41.8C in the city of Isesaki.
Major cities experienced unusually high numbers of extremely hot days. Tokyo recorded 25 days above 35C compared with an average of just 4.5 days. Kyoto saw 52 days above 35C against a typical average of 18.5 days.
Context of Increasing Heat
Extreme weather events such as heatwaves have become more common and more intense in many parts of the world. Japan’s new naming system aims to help people better understand and prepare for dangerous heat levels. The introduction of kokushobi highlights the country’s response to changing climate patterns and their impact on daily life.
The Japan Meteorological Agency continues to monitor temperatures closely and provides forecasts that indicate a high probability of above-normal temperatures for the coming summer months.
Categories and Keywords
Categories: Science Climate Weather Japan Environment.
Keywords: Japan kokushobi 40C heat extreme temperatures hottest summer Japan Meteorological Agency heatwave climate record Isesaki Tokyo Kyoto.
Impact of Extreme Heat on Japan
The introduction of the new term kokushobi follows a summer that shattered previous temperature records across Japan. Average temperatures were significantly higher than normal and the number of extremely hot days increased dramatically in many regions. These conditions highlight the growing frequency of severe heat events in the country.
The Japan Meteorological Agency has expanded its heat category system to better inform the public about dangerous temperature levels. The existing terms for 25C, 30C and 35C days are now joined by this new designation for 40C and above.
Public Engagement Through Naming
The national survey that selected kokushobi received hundreds of thousands of responses showing strong public interest in how extreme heat is described. The chosen name emphasises the harsh and severe nature of such high temperatures. This approach aims to raise awareness and encourage appropriate precautions during future heatwaves.
The agency hopes the clearer terminology will help people recognise the risks associated with 40C-plus days and take necessary protective measures.
Forecasts for the Coming Summer
The Japan Meteorological Agency has already issued forecasts indicating a high probability of above-normal temperatures from June to August this year. This prediction comes after the record-setting conditions experienced in 2025 when multiple locations broke local temperature records.
The cumulative number of extremely hot days last summer exceeded the previous record set in 2024 showing a clear upward trend in intense heat events.
Broader Significance
Japan’s decision to name days reaching 40C or hotter reflects a wider global pattern of increasing extreme weather linked to climate factors. The new term kokushobi provides a specific label that can be used consistently in weather reports and public communications. This helps improve understanding of heat risks across different regions of the country.
The development demonstrates how meteorological agencies are adapting their language and warning systems in response to changing climate conditions and more frequent record-breaking temperatures.
Categories and Keywords
Categories: Science Climate Weather Japan Environment.
Keywords: Japan kokushobi 40C heatwave Japan Meteorological Agency hottest summer record temperatures climate Isesaki Tokyo Kyoto extreme weather.
Japan reveals new name for 40C-and-hotter days after blistering summer
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