The central Japan city of Sanjo registered a temperature of 40.4 C on Thursday, a national record high for September, as a wide area along the Sea of Japan coast witnessed extraordinary heat.
The Japan Meteorological Agency said the intense heat in the city in Niigata Prefecture may have been caused by a Foehn wind -- a warm, dry gust periodically descending the leeward slope of a mountain.
The agency also said warm air from the East China Sea blew toward Typhoon Maysak that moved north over the Sea of Japan.
It was the first time that the mercury topped 40 C in Japan in September. The previous record for the month was 39.7 C registered in Kumagaya in Saitama Prefecture, near Tokyo, on Sept. 2, 2000.
Temperatures also soared Thursday in northeastern Japan cities along the coast, logging 39.1 C in Tsuruoka, Yamagata Prefecture, according to the agency.
Some other cities experienced temperatures over 38 C, such as Wajima, Ishikawa Prefecture, with 38.6 C.
Many areas in prefectures including Hokkaido, Aomori, Akita, Yamagata, Toyama and Ishikawa renewed their temperature records for September.
The highest-ever temperature in Japan of 41.1 C was recorded last month in Hamamatsu, Shizuoka Prefecture, and in Kumagaya in July 2018.
The weather agency also warned that powerful Typhoon Haishen could reach waters around the Amami island chain in Japan's southwest as early as Sunday and pass through the Kyushu region.