Midsummer day (manatsubi)

Definition: the temperature that makes a midsummer day

JMA forecast terminology defines it as "a day with a daily maximum temperature of 30 degrees or higher" (source: JMA, Terms used in weather forecasts: temperature and humidity, in Japanese, accessed August 17, 2026).

Midsummer days in Tokyo

Days per year (1996–2025)

Number of midsummer 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: 2023 (90 days), 2025 (88 days), 2024 (83 days) (records 1875–2025; days with observations only).

More about the midsummer day

A midsummer day is a day on which the daily maximum temperature is 30°C or higher. It is a mark one step above 25°C, the line for a summer day; once this line is crossed, you start sweating just by standing in the sun, and even indoors, airflow alone is no longer enough to stay comfortable. It is a line often used to describe summer heat in a few words.

Midsummer days have long served as a yardstick of summer's strength because they strike a balance between being easy to count and matching how heat feels. Extremely hot days (35°C or higher) do not add up unless the year is very hot, while summer days (25°C or higher) pick up a wide span from early summer to early autumn. Midsummer days, in between, offer the right level of detail to compare the strength of summer from year to year.

All three lines are set by the daily maximum temperature alone, without regard to that day's humidity or wind. So even on the same midsummer day, the heat of a dry highland and the heat of a lowland wrapped in humid air from the sea feel completely different on the body. The same number does not always mean the same thing, which is worth keeping in mind when reading day counts.

In Tokyo, a warm day in May sometimes becomes a midsummer day, and midsummer days appear over a long period: during sunny breaks in the rainy season, at the height of summer after the rainy season ends, and through the lingering heat of September. This page shows the year-by-year change in the number of midsummer days in Tokyo and this year's situation across Japan. There is also a page summarizing the normal start and end dates of the rainy season, so you can compare them with the progress of the seasons.