The Japan Meteorological Agency said Sunday that the rainy season in the Shikoku region has ended five days earlier than the climatological average [1].
This sudden shift in weather patterns has accelerated the onset of extreme summer heat, increasing the risk of heat-related illnesses across western Japan. The transition from heavy rains to intense sunlight has allowed a strong high-pressure ridge to dominate the region.
Local prefectural health authorities have issued heat-stroke alerts for 12 prefectures in western Japan [2]. The alerts come as temperatures in the Kyushu region climb toward 40°C [2].
In Fukuoka, temperatures have exceeded 35°C for three consecutive days [2]. Forecasts for Fukuoka and Kumamoto suggest temperatures will reach 38°C [2]. The heat is expected to be even more intense in Oita, where the maximum temperature for Hita is forecast at 39°C [2].
Other areas are already seeing prolonged heat. Matsuyama has experienced six consecutive midsummer days [2].
The Japan Meteorological Agency said the early end of the rainy season reduced cloud cover, which facilitated the rapid rise in temperature. This combination of high heat and humidity typically increases the physiological strain on the human body, making hydration and cooling centers critical for public safety.
“The rainy season in the Shikoku region ended five days earlier than the climatological average.”
The early conclusion of the rainy season in Shikoku creates a compressed transition into extreme summer heat, leaving residents and infrastructure less time to adapt. When temperatures approach 40°C in tandem with Japan's high summer humidity, the risk of heat-stroke spikes, placing significant pressure on regional healthcare systems in western prefectures.
