Photo/Illutration Tourists stroll with sun umbrellas to Dazaifu Tenmangu shrine in Dazaifu, Fukuoka Prefecture, as the summer heat lingers on Sept. 18. (Mizuki Enomoto)

Japan experienced its second-hottest September on record, with the average temperature 2.52 degrees higher than normal, the Japan Meteorological Agency announced on Oct. 1.

This September ranks just behind last year’s, which remains the hottest ninth month of the year since Japan began keeping such records in 1898, with an average temperature 2.66 degrees higher than normal.

Eastern Japan, western Japan and the Okinawa Amami region each experienced their hottest September ever recorded, with average temperatures reaching 3.2, 3.4 and 1.1 degrees above normal, respectively.

This year a record-breaking 1,452 locations across the country recorded “extremely hot weather,” defined as temperatures hitting 35 degrees or higher, in September.

This figure surpasses the previous record of 1,093 locations set in 2010, making it the highest number since comparable data became available in that year.

The intense summer heat also continued well into the second half of the month.

On Sept. 20, extremely hot weather was recorded at 28 locations, including Atami, Shizuoka Prefecture, and Iizuka, Fukuoka Prefecture. Temperatures also exceeded 35 degrees in Owase, Mie Prefecture, the following day.

As a result, 45 of the 153 observation points nationwide broke the record for the latest date of extremely hot weather.

“The progression of the seasons is delayed. Even in September, we often experienced summer-like atmospheric pressure patterns,” said Hisashi Nakamura, a professor at the University of Tokyo’s Research Center for Advanced Science and Technology specializing in climate change.

He explained that the extension of the Pacific high pressure system, combined with the northward meandering of the westerlies, caused Japan and its surrounding areas to be covered by high pressure, resulting in clear skies and rising temperatures.

Sea surface temperatures have also been high, leading to an increase in water vapor. This has contributed to the formation of linear rainbands, resulting in the recent devastating heavy rainfall over the Noto Peninsula.

“Heat directly affects the amount of rainfall,” Nakamura warned. “We must be prepared for heavy rain similar to what the Kyushu and Shikoku regions typically experience, even in areas such as Hokuriku and Tohoku, where rainfall has not traditionally been high.”

Despite the saying, “heat waves don’t last beyond the equinox,” hot days exceeding 30 degrees are forecast for October, prompting warnings about the risk of heatstroke.

Nakamura said that it’s still too early to conclude whether this prolonged heat in autumn is becoming the new normal.

“Due to global warming, the trend of rising temperatures will continue,” he said. “Keeping in mind that the climate is changing, society needs to adapt by changing plans for sports events and agricultural activities, without being bound by traditional calendars or customs.”

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