Large hail and sudden “guerrilla” thunderstorms struck multiple regions across Japan on May 13, 2026 [1].

These volatile weather patterns highlight the increasing unpredictability of spring transitions, where intense heat rapidly shifts into severe storms that threaten urban infrastructure and public safety.

The storms impacted several major areas, including the Shibuya district in Tokyo, Uji City in Kyoto Prefecture, and Ashiya City in Hyōgo Prefecture [1], [2]. In Ashiya, the storms resulted in localized flooding and the fall of large hail [1], [2].

Residents described a jarring transition in weather. One male resident said the change was rapid, noting it had been sunny and warm like mid-summer before the temperature dropped [1]. In Uji City, temperatures had reached near 30 °C [1] before the atmospheric instability triggered the storms.

Footage from the event captured the immediate impact on pedestrians. One person leaving a convenience store said, "It hurts, it hurts," while being struck by the hail [1].

The phenomenon was driven by an unusually unstable atmosphere that followed a period of intense summer-like heat [1], [2]. Meteorologists expect these unstable conditions to continue through May 14, 2026 [2]. While some reports suggest the instability could extend to May 15, the primary forecast focuses on the immediate 24-hour window [2].

““It hurts, it hurts,””

The occurrence of 'guerrilla' thunderstorms—characterized by their sudden onset and localized intensity—suggests a volatile atmospheric state where high surface temperatures collide with unstable upper-air conditions. This pattern increases the risk of flash flooding in densely populated urban centers like Shibuya and Ashiya, where drainage systems can be quickly overwhelmed by short-duration, high-volume precipitation.