Northern Japan experienced record-breaking heavy rain Sunday, while western regions faced an extreme heat wave and heatstroke warnings [1].
These simultaneous weather extremes place a significant strain on national emergency services and public health systems across the archipelago. The contrast between flood risks in the north and lethal heat in the south highlights the volatile nature of the current summer season.
In Hokkaido's Toya Lake Onsen area, the Japan Meteorological Agency reported 112.0 mm of rain within 24 hours [1]. This amount is equivalent to the entire average rainfall for the month of July in that area [1]. The agency issued warnings for landslides and floods as a low-pressure system and weather front drew warm, moist air from the south to intensify the precipitation [1, 3].
Meanwhile, western Japan is struggling with a persistent summer heat wave. In Tokyo, temperatures reached 30 °C shortly after 8 a.m. on Sunday [1]. This marks the sixth consecutive day that Tokyo has experienced a "midsummer day," defined as temperatures reaching 30 °C or higher [1].
Forecasters expect the heat to intensify. The maximum temperature in Tokyo is predicted to reach 33 °C [1]. Other regions, including Kyoto's Maizuru area and Tottori, are facing even more extreme conditions with forecast highs of 37 °C [1].
Local authorities have urged residents in the west to take strict precautions against heatstroke. In the north, officials said residents should remain vigilant regarding soil stability and rising water levels to prevent casualties during the storms [1, 3].
The Japan Meteorological Agency said there was a risk of heavy rain across northern and eastern Japan starting from July 16 through July 18 [4].
“Hokkaido's Toya Lake Onsen area saw 112.0 mm of rain in 24 hours, matching the typical July monthly total.”
The simultaneous occurrence of record-breaking precipitation in Hokkaido and extreme heat in the western prefectures demonstrates a dangerous atmospheric divergence. When a low-pressure system pulls moist southern air northward, it can trigger localized flooding in the north while leaving the south trapped under a high-pressure heat dome, increasing the risk of both natural disasters and public health crises.
