Japan Endures Hottest Summer on Record in 2025

The Japan Meteorological Agency announced that the average temperature this summer (June to August) was 2.36° Celsius higher than the normal level (based on the 30-year average up to 2020), thus marking the hottest summer since records were first kept in 1898. This year’s average far exceeds the previous hottest summers recorded in 2023 and 2024, when temperatures were 1.76° above normal.

Throughout the summer of 2025, the westerly jet stream generally flowed more to the north than usual, bringing in warm air that raised temperatures noticeably in northern, eastern, and western Japan. Out of the 153 meteorological stations nationwide, 132 recorded their highest average summer temperature on record.

The breakdown by month shows that June and July, respectively, were 2.34° and 2.89° above normal, marking a record statistical high for both months. August, meanwhile, was 1.84° above normal, for the second highest level on record.

On August 5, a temperature of 41.8° was recorded in the city of Isesaki in Gunma Prefecture. This is the highest temperature ever recorded in Japan. In 2025, temperatures of 40° or higher were recorded in 30 locations in 13 prefectures across a period of nine days. This is the largest number of prefectures and locations since comparable statistics were first kept in 2010.

Data Sources

• Data on temperatures from June to August 2025 (Japanese) from the Japan Meteorological Agency.
• Data on average seasonal temperatures in Japan (Japanese) from the Japan Meteorological Agency.

(Translated from Japanese. Banner photo: Women in yukata hold portable fans as they walk along the Nakamise street in Asakusa, Tokyo. © Reuters.)