Severe "guerrilla" thunderstorms and hail struck several areas of the Kanto region starting Friday morning [2].
These sudden weather events caused significant disruptions to transportation and public safety, leading to urban flooding and dangerous visibility conditions for drivers and pedestrians.
The storms began around 11:30 a.m. on June 12 [2]. The Japan Meteorological Agency issued Level 3 heavy rain warnings for multiple areas, including Tokyo's Tachikawa City, Koganei City, and Adachi Ward [1].
In Saitama Prefecture, hail accumulated on roads in Hanno and Iruma cities, creating river-like flows of ice that blocked traffic [1]. The rapid development of rain clouds was driven by a sharp contrast between cold air in the upper atmosphere and rising surface temperatures, particularly along mountainous areas [4].
Witnesses described the intensity of the downpour as overwhelming. "If you were outside, you'd be finished," a person filming the scene said [5].
Forecasters said that the unstable atmospheric conditions would persist through Saturday, June 13 [3]. Residents in the Kanto region were advised to remain vigilant for further sudden thunderstorms and potential flooding as the system continues to move through the area.
“"If you were outside, you'd be finished,"”
The occurrence of 'guerrilla rainstorms'—characterized by their sudden onset and localized intensity—highlights the increasing volatility of regional weather patterns in Japan. The combination of rapid surface warming and cold upper-air currents creates a high-risk environment for urban flash flooding, which can overwhelm drainage systems in densely populated areas like Tokyo and Saitama.
