Japan has experienced more extreme rainfall in recent days, following an “unprecedented” deluge in Chiba in mid-August. Moisture from the Sea of Japan brought relentless heavy rain to the prefectures of Ishikawa and Toyama on Thursday. In Himi, Toyama, 361.5mm of rain fell in 24 hours, equivalent to half the average annual rainfall in London and Paris. As a result of the downpours, several rivers burst their banks, leading to flash floods and mudslides with trees felled and buildings damaged.
Warnings and evacuations issued
Japan’s Meteorological Agency issued its highest-level rain warning within the two prefectures earlier in the week as well as landslide warnings, leading to the evacuation of hundreds of thousands from the region. Models on Thursday indicated there could be a further 200mm of rain just south of this region as it continues to come in from the west.
Typhoon Saudel and El Niño influence
Two days before, Typhoon Saudel had passed through Kagoshima and Okinawa Island prefectures south-west of the mainland, bringing 100mph (160km/h) winds in addition to extreme rainfall, including in the Amami region where 230mm rain fell in a day. This storm was forecast to move into south-east China at the end of this week, but with its winds much reduced.
While the warm ocean water surrounding Japan has often led to an increase in the number of typhoons at this time of year, this year’s developing El Niño could explain why so many have approached the island nation and why there have been so many extreme rain events. Unlike during La Niña years when the semi-permanent North Pacific High often extends west in Japan, in El Niño years, this ridge tends to extend northwards, allowing weather fronts to push through more easily and tropical storms that have developed farther south to “re-curve” towards Japan.
Severe storms in western Europe
Over the past few days severe convective storms have struck in western Europe, notably around Alpine regions. The storms have brought intense rain, strong winds, large hail and even tornadoes. Spain, France, and Italy have been particularly affected, with hailstones as large as 10cm in diameter being reported in Catalonia and a significant tornado developing in the village of Pomas in south-west France.
The severe weather developed due to a combination of factors, including a low-pressure system tracking along the western coast of Europe, high levels of convective instability, and strong vertical wind shear.
