Severe Storms Bring Extreme Rainfall to Japan and Destructive Weather to Western Europe

Extreme weather events featuring intense rainfall, powerful winds, and violent storms have struck regions across Japan and western Europe, prompting widespread emergency evacuations and inflicting significant structural damage.

In central Japan, heavy atmospheric moisture flowing from the Sea of Japan produced relentless downpours across Toyama and Ishikawa prefectures. The rainfall was particularly severe in Himi, a city in Toyama prefecture, where 361.5 millimeters of rain fell within a 24-hour period. This single-day measurement represents roughly half of the average annual rainfall recorded in cities such as London or Paris. The intense deluge caused several rivers to overflow their banks, generating widespread flash floods and triggering mudslides that damaged and knocked down buildings.

Following the flooding, Japan’s Meteorological Agency elevated its rain warnings to the highest possible level for both Toyama and Ishikawa prefectures, while also issuing emergency landslide warnings. The emergency directives led authorities to call for the evacuation of hundreds of thousands of residents. Predictive atmospheric models indicated that an additional 200 millimeters of precipitation could affect regions situated immediately south of the affected area as moist air masses sustained their westward movement.

The severe weather in Toyama and Ishikawa followed a record-breaking deluge in Chiba prefecture in mid-August. Just two days prior to the heavy rains in the central prefectures, Typhoon Saudel swept through southwestern Japan, affecting Kagoshima prefecture and Okinawa Island. The typhoon recorded wind speeds of up to 160 kilometers per hour (100 miles per hour) and dumped 230 millimeters of rain within 24 hours across the Amami region. The storm was projected to track toward southeastern China while weakening significantly.

Meteorologists attributed the frequency of extreme rainfall events and approaching storms in Japan to a developing El Niño pattern alongside warm surrounding ocean waters. During El Niño conditions, the North Pacific High ridge shifts northward rather than extending westward toward Japan as it typically does during La Niña years. This atmospheric shift allows frontal systems to move through more easily and permits tropical storms originating further south to curve back toward the Japanese archipelago.

Concurrently, severe convective weather systems impacted parts of western Europe, heavily affecting Spain, France, and Italy, particularly in regions around the Alps. Driven by a low-pressure system tracking along Europe’s western coastline, high convective instability, and strong vertical wind shear, the storms produced intense precipitation, destructive winds, large hail, and tornadoes. In Catalonia, Spain, hailstones measuring up to 10 centimeters in diameter were recorded, while a significant tornado destroyed homes in the village of Pomas in southwestern France.

Background

Late summer frequently brings heightened tropical storm activity to East Asia, driven by elevated ocean surface temperatures in the western Pacific Ocean. The arrival of an El Niño climate pattern alters standard atmospheric pressure ridges, shifting weather tracks and increasing the likelihood of tropical storms and heavy rainfall fronts steering directly toward the Japanese islands.

In western Europe, late summer weather can produce sharp temperature contrasts and high atmospheric instability, particularly when Atlantic low-pressure systems interact with warm air over land. These conditions frequently fuel convective storm cells capable of producing localized severe weather, including torrential downpours, damaging hail, and rare tornadoes.