The Japan Meteorological Agency forecasts the Kanto region will experience its first day of the year reaching 40 °C tomorrow [1].
This sudden spike in temperature follows the expected end of the rainy season, signaling a volatile transition into summer that could trigger health risks and infrastructure strain. The rapid rise in heat is occurring alongside unstable weather patterns that may bring severe precipitation to specific inland areas.
Forecasters expect the extreme heat on July 21, with temperatures reaching 40 °C [1]. This heatwave is linked to the conclusion of the rainy season, which typically leads to a sharp increase in temperatures across the region [3].
While much of the region faces extreme heat, Gunma and Tochigi prefectures are under a heavy-rain warning. Reports on the timing of these rains vary; some indicate warnings for tomorrow, July 21, while other reports suggest warning-level heavy rain for the Kyushu-Kanto area on July 22 [2, 3].
These precipitation warnings are driven by an approaching weather front and the potential for typhoons [3]. The volatility of the current season is evidenced by recent records in other areas; for example, Amami City recorded over 1,000 mm of rainfall between May 3 and June 30 [3].
Local authorities are monitoring the situation as the Kanto region prepares for the dual threat of record-breaking heat and sudden flooding. The JMA said the combination of the rainy season's end and atmospheric instability is creating these divergent weather extremes [3].
“The Kanto region will experience its first day of the year reaching 40 °C tomorrow”
The simultaneous occurrence of 40 °C heat and heavy-rain warnings highlights the increasing volatility of Japan's summer weather transitions. The shift from the rainy season to extreme heat can lead to a higher incidence of heatstroke and flash flooding, requiring coordinated emergency responses across different prefectures.
