HOKKAIDO, Oct 02, 2025 (News On Japan) - Heavy rainfall battered parts of Hokkaido, with some areas receiving more than a month’s worth of precipitation in only six hours, prompting flood warnings and evacuation advisories. Meteorologists are saying the downpour was the result of a combination of unstable atmospheric conditions and moist air flowing in from the sea.
In Shiraoicho, a weather report received at 7:10 a.m. on October 1st described rain so heavy that visibility dropped sharply, accompanied by occasional lightning and thunder. By 10:35 a.m., residents reported roads in front of their homes had turned into rivers, and evacuation orders were issued as the rain intensified.
Observations confirmed record-breaking volumes, including 123.5 millimeters in a single hour at Morino and over 80 millimeters at several other sites in Hokkaido. Total rainfall in some areas reached 358 millimeters over a 12-hour period, levels described by forecasters as unprecedented.
Weather analysts explained that the cause lay in a combination of systems. A high-pressure zone to the east of Hokkaido funneled warm, moisture-laden air from the south, while a nearby low-pressure area and upper-level cold air at minus 18 degrees created strong atmospheric instability. These conditions, combined with local topography, caused strong upward air currents and the rapid development of rain clouds.
The narrow but intense band of rainfall repeatedly struck the same coastal zones in the Iburi region, particularly around Tomakomai, creating the risk of localized flooding and landslides. Forecasters warned that heavy rains could persist into the late hours of the evening in the same areas, rather than spreading widely.
Authorities urged residents in affected regions to remain on high alert for landslides and other disasters as ground saturation increases.
Source: ウェザーニュース
