1290. Report on the June 2025 Heat Wave in the Northern Hemisphere

According to the Japan Meteorological Agency, the Pacific high-pressure system extended strongly toward Japan in June this year, making the deviation from the standard value of the monthly average temperature in Japan +2.34°C, exceeding the previous June record of +1.43°C in 2020, and the highest since statistics began in 1898. In addition, the average sea surface temperature in June near Japan was +1.2°C (preliminary value), tying with 2024 for the highest June record since statistics began in 1982.

Europe and North America were also hit by a fierce heatwave this June. According to the European Space Agency, a fierce heatwave hit large areas of Southern Europe and North Africa, causing temperatures to exceed the seasonal average and health and wildfire warnings to be issued over a wide area. Spain, France, Italy, Greece, Cyprus, and Algeria were particularly hard hit. The current heatwave is caused by a high-pressure system stagnating over Western Europe, commonly known as a "heat dome." This high-pressure system acts like a lid, trapping hot, dry air and causing temperatures to rise over time. As it moves eastward, it also attracts heat from North Africa, further exacerbating the heatwaves across the region.

According to the World Meteorological Organization, in Western and Southwestern Europe, both the minimum (representing nighttime temperatures) and maximum (usually occurring in the afternoon) temperatures broke monthly records for June in some areas. A high of 46.0°C was recorded in southern Spain, with temperatures exceeding 40°C over a wide area. This heatwave is exceptional not only for its magnitude, but also for its timing, since such heatwaves usually occur in midsummer. Sea surface temperatures (SSTs) in the Mediterranean Sea are also unusually high for this time of year, which tends to exacerbate the heatwaves over land. In contrast, in the Southern Hemisphere winter, South America experienced an unusual record-breaking cold spell in June, especially in Argentina, Chile, and Paraguay.

Contributor: Miyuki IIYAMA, Information Program