The Japan Meteorological Agency warned that East Japan will remain meteorologically unstable while West Japan faces heavy-rain alerts on June 29, 2026 [1].
These conditions pose significant risks to public safety and infrastructure across the archipelago. The combination of unstable atmospheric conditions in the east and the progression of the rainy season in the west increases the likelihood of flash floods and dangerous lightning strikes.
According to the agency, a low-pressure system combined with upper-level cold air is expected to destabilize the atmosphere nationwide [2]. This pattern has created a window of instability from June 28 to June 29, 2026 [2]. The agency said that people in a wide area should be cautious of lightning, sudden gusts, strong winds, and high waves [2].
In East Japan, including the Kanto region and surrounding prefectures, the weather is expected to remain unstable [1]. Residents in these areas, as well as those in North Japan, may experience sudden rain or thunderstorms [3]. Despite the instability, some regions in Kanto and Tokai are expected to see summer daytime temperatures of 25 °C or higher [4].
Meanwhile, West Japan has entered the latter half of the rainy season [1]. This transition has prompted officials to issue heavy-rain warnings for the region. The agency said that the interaction between the seasonal rain front and the current low-pressure system is driving the increased precipitation risk [1].
Local authorities are monitoring river levels and slope stability to prevent landslides. The agency said that citizens should stay updated on the latest weather advisories as the low-pressure system moves across the country [2].
“East Japan, including the Kanto area, would stay meteorologically unstable while West Japan entered the latter half of the rainy season.”
The simultaneous occurrence of atmospheric instability in the east and the peak rainy season phase in the west creates a dual-threat scenario for Japan. This requires a coordinated national response to manage both sudden, localized storm events in urban centers like Tokyo and sustained, heavy precipitation in western rural areas, which are more susceptible to landslides.
