Sudden "guerrilla" thunderstorms swept across Japan on June 13 and 14, producing heavy rain, hail, and widespread road flooding [1, 2, 3, 4].
These rapid weather shifts highlight the increasing volatility of regional climates, where extreme precipitation occurs with little warning and disrupts critical infrastructure.
In Hokkaido, weather conditions shifted abruptly on the morning of June 13, leading to flooded roads [4]. In Asahikawa, authorities issued a Level 4 landslide disaster warning [4]. Masamitsu Ito of the Asahikawa City Science Museum and Observatory said hailstones measuring approximately one to 1.5 centimeters fell during the storm. Ito said such intensity is rare and occurs only once every few years [1].
The storms continued into the following day. On June 14, a guerrilla thunderstorm hit Kanagawa Prefecture around 3:30 p.m. [2]. The storm caused power outages affecting more than 10,000 households in the region [2].
Similar disruptions were reported in the Kanto region, including Tokyo, as well as Sapporo and Ishikari in Hokkaido [1, 2, 3, 4]. Experts attribute these sudden developments to unstable atmospheric conditions amplified by unusually high summer temperatures [5, 6]. These conditions created a catalyst for the rapid formation of intense storm cells.
Local reports emphasized that the speed of the weather change left residents and commuters with minimal time to seek shelter. The combination of seasonal heat and atmospheric instability transformed standard summer weather into a series of high-impact events across the archipelago [6].
“Such intensity is rare and occurs only once every few years.”
The occurrence of 'guerrilla rainstorms'—a term used in Japan to describe sudden, localized torrential downpours—underscores the challenge of predicting hyper-local weather events. When high summer temperatures collide with unstable air masses, the resulting storms can overwhelm urban drainage systems and power grids rapidly. This pattern suggests that traditional forecasting may struggle to keep pace with the increasing frequency of extreme, short-term weather anomalies.
