Japan recorded a record-breaking number of mid-summer days on Saturday, with more than 570 locations hitting the threshold [1].
This unprecedented heat spike during mid-May suggests an unusually early shift in seasonal patterns. The surge in temperatures coincides with major cultural events, putting participants and spectators at risk of heat-related illness during outdoor activities.
Strong sunshine and warm air drove temperatures up across the country, particularly in western Japan. The highest temperature was recorded at 32.6 °C in Akiota-cho, Hiroshima Prefecture [1]. This follows a trend of early warmth this year, including a day on April 28 when more than 220 locations recorded summer-day temperatures of 25 °C or higher [5].
In Tokyo, the heat peaked during the second day of the Sanja Festival in Asakusa. Approximately 100 portable shrines took part in the procession [1]. Despite the intensity of the sun, the festival proceeded with high energy. One participant said, "It is hot. It is the best!" [2].
Other attendees noted that the heat felt even more intense than the official readings. One festival participant said the perceived temperature felt to be around 35 °C [3].
While some reports indicated more than 200 mid-summer locations on May 20, the data from Saturday remains the most significant peak of the season [4]. The record of over 570 locations is described as the most ever recorded for this period [1].
“"It is hot. It is the best!"”
The recording of over 570 mid-summer days in mid-May represents a significant departure from historical climate norms in Japan. When record-breaking heat arrives before the official start of summer, it complicates public health planning for massive outdoor gatherings like the Sanja Festival and may signal a more volatile temperature trajectory for the coming months.
