Temperatures in Japan's Kanto-Koshin region are forecast to reach 40 °C today, July 21, 2026 [1].
This weather event is significant because it could mark the first nationwide "酷暑日" (extremely hot day) since the term was introduced nine years ago [1]. Such extreme heat increases the risk of public health crises and puts immense pressure on the national power grid.
Forecasters expect Kumagaya in Saitama to hit 40 °C [1]. Other cities, including Maebashi in Gunma, Nagoya in Aichi, and Gifu in Gifu prefecture, are expected to reach 39 °C [1]. The heat is driven by a strong high-pressure ridge covering Japan, which has caused temperatures to rise rapidly from the morning onward [1].
Early readings on Tuesday already showed the intensity of the heatwave. Temperatures reached 35 °C in Osaka and Nagoya earlier in the day [1]. The Tokai area is also experiencing similar extreme conditions as the high-pressure system persists.
Authorities have issued a heat-stroke alert for the day [2]. The warning urges residents to take strict precautions against heatstroke as temperatures peak in the afternoon. Local officials are monitoring the situation in the Kanto-Koshin and Tokai regions to prevent heat-related illnesses.
The designation of a "酷暑日" is a specific meteorological marker used in Japan to categorize days of extreme heat. If the 40 °C threshold is observed today, it will be the first time the nationwide criteria for this term have been met in nearly a decade [1].
“Temperatures in Japan's Kanto-Koshin region are forecast to reach 40 °C today.”
The potential for a nationwide 'extremely hot day' highlights the increasing frequency of extreme thermal events in Japan. When temperatures hit 40 °C, the risk of heatstroke rises exponentially, particularly for the elderly and outdoor workers. This event underscores the ongoing challenge of urban heat islands in cities like Nagoya and Kumagaya, where concrete infrastructure traps heat, necessitating more aggressive public health interventions.
