Scorching day (kokushobi)

Definition: the temperature that makes a scorching day

JMA forecast terminology defines it as "a day with a daily maximum temperature of 40 degrees or higher" (source: JMA, Terms used in weather forecasts: temperature and humidity, in Japanese, accessed August 17, 2026).

Scorching days in Tokyo

Days per year (1996–2025)

Number of scorching days per year, counted from observations in Tokyo (Kitanomaru Park, Chiyoda City). The station moved from Otemachi in December 2014, so the series may not be continuous across the move. Most on record: 2025 (0 days), 2024 (0 days), 2023 (0 days) (records 1875–2025; days with observations only).

More about the scorching day

A scorching day is a day on which the daily maximum temperature is 40°C or higher. The Japan Meteorological Agency (JMA) lists it with this definition among the terms it uses in weather forecasts (as of August 17, 2026). It is a line one step above 35°C, the line for an extremely hot day.

The figure of 40°C is not the temperature of sunlit ground or the inside of a closed car. Air temperature is measured for air in a ventilated place, under conditions that avoid the effects of direct sunlight and heat from the ground. When that value reaches 40°C, it means not that some spot got hot, but that the air of that area itself was heated considerably.

The daily maximum temperature climbs this high when several conditions overlap. Commonly cited situations for high temperature records include the phenomenon in which wind blowing down over mountains dries out and warms up, basins surrounded by mountains where daytime heat has trouble escaping, and warm air covering the area high into the sky. These are the reasons why high records tend to cluster inland rather than on plains near the sea.

This page shows how the number of days in Tokyo that count as scorching days has changed over time, alongside this year's situation across Japan. Comparing it with the page on extremely hot days shows that days appear in completely different ways at the 35°C line and the 40°C line. If there is an area you are curious about, you can trace the temperatures recorded there from each station's page.