The Japan Meteorological Agency said Sunday that the rainy season has begun in the Tokai and Kanto-Koshin regions [1].
This seasonal transition brings immediate risks of severe weather across the archipelago. The agency said that unstable atmospheric conditions are currently affecting Western Japan, increasing the likelihood of landslides and rising river levels.
According to the agency, the arrival of the rainy season in the Tokai region occurred one day later than average [2]. In contrast, the start of the season for the Kanto-Koshin region was described as being on par with typical years [3].
Forecasters are monitoring a period of instability lasting through noon on June 8 [1]. The agency said the influence of a seasonal rain front and low-pressure systems are the primary causes of the current atmospheric volatility [1].
Specific warnings have been issued for the Shikoku region, where rainfall is expected to reach 200 millimeters [4]. The agency said that residents should remain vigilant regarding potential landslides, and the swelling of rivers due to this concentrated precipitation [4].
While the rainy season has officially arrived in the east and center of the country, the agency continues to track the movement of these weather systems across Western Japan to determine the scale of potential flooding [1].
“The rainy season has begun in the Tokai and Kanto-Koshin regions.”
The arrival of the rainy season in Tokai and Kanto-Koshin marks a critical shift in Japan's annual weather pattern, moving the risk of heavy precipitation from the south toward the more densely populated central and eastern corridors. The immediate forecast of 200 millimeters of rain in Shikoku underscores the volatility of the current rain front, suggesting a high risk of flash flooding and soil instability before the weather stabilizes across the rest of the country.
