Japan Experiences Hottest Summer on Record; June-August Temperatures Soar 2.36 C Above 30-Year Average

The Yomiuri Shimbun

15:36 JST, September 2, 2025

Japan’s average temperature this summer, from June to August, exceeded the 30-year average by 2.36 C, hitting its highest point since records began in 1898, the Japan Meteorological Agency (JMA) announced on Monday.

Record-breaking high temperatures were reported this summer, as the season’s “abnormal heat,” in the words of the JMA, pushed the mercury to 35 C or above in more locations than ever previously recorded.

The Agency analyzed this summer’s average temperatures at 15 locations across the country where long-term observations have been conducted and where the impact of urbanization is relatively small. The results showed temperatures were 2.36 C higher than the average from 1991 to 2020, greatly surpassing the previous record high of 1.76 C, set in 2023 and matched in 2024.

Regional analysis based on data from 149 locations nationwide showed temperatures 3.4 C higher than the 30-year average in Northern Japan, 2.3 C higher in Eastern Japan and 1.7 C higher in Western Japan. All regions recorded their highest temperatures since statistics began in 1946.

Temperatures of 40 C or higher were recorded 30 times in various locations, with the highest in Japan, 41.8 C, seen in Isesaki, Gunma Prefecture, on Aug. 5. There were a total of 9,385 recorded temperatures in excess of 35 C, the highest number since 2010, when comparable data became available.

According to the JMA, factors contributing to the extreme heat included a Pacific high-pressure system that covered Honshu, leading to many days of clear skies and high temperatures.

Yoshinori Oikawa, head of the JMA’s Center for Information on Climate Extremes, said, “These high temperatures and weather conditions are abnormal across 130 years of statistical data.”

The extreme heat is expected to continue into September, with temperatures above 35 C forecast for roughly the next two weeks, mainly in eastern and western Japan. The JMA is urging caution against heatstroke.