Extremely hot day (moshobi)

Definition: the temperature that makes an extremely hot day

JMA forecast terminology defines it as "a day with a daily maximum temperature of 35 degrees or higher" (source: JMA, Terms used in weather forecasts: temperature and humidity, in Japanese, accessed August 17, 2026).

Extremely hot days in Tokyo

Days per year (1996–2025)

Number of extremely hot 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 (29 days), 2023 (22 days), 2024 (20 days) (records 1875–2025; days with observations only).

More about the extremely hot day

An extremely hot day is a day on which the daily maximum temperature is 35°C or higher. Like summer days (25°C or higher) and midsummer days (30°C or higher), it is a line set by the daily maximum temperature alone, and it sits highest of the three. The Japan Meteorological Agency (JMA) lists these three side by side among the terms it uses in weather forecasts (as of August 17, 2026).

The number of extremely hot days tends to swing widely from year to year. Summer days and midsummer days reach a fair number every year, but extremely hot days split into years when they hardly appear and years when they come one after another, depending on how summer air masses move in and how long sunny weather lasts after the rainy season ends. So rather than calling a single year's count high or low, looking at several years side by side makes it easier to grasp the character of summer in that area.

Above the 35°C line, the air itself holds heat even in the shade, and a breeze does little to cool you down. This line is widely used in daily life as a cue to rearrange plans for outdoor work and exercise, and how to take water and breaks.

On preparing for heat, public agencies such as JMA and the Ministry of the Environment publish information matched to the level of heat on a given day, along with points to watch in daily life. When deciding what to actually do, please check the guidance from those public agencies. This page lists temperature records and does not give health advice.

This page shows the year-by-year change in the number of extremely hot days in Tokyo and this year's situation across Japan. Viewed alongside the pages on midsummer days and scorching days (40°C or higher), it shows how far up the staircase each year's heat reached.