After an “unprecedented” deluge in Chiba in mid-August, Japan has experienced further extreme rainfall in recent days. 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. Several rivers burst their banks, triggering flash floods and mudslides, felling and damaging buildings.
Japan’s Meteorological Agency issued its highest-level rain warning for the two prefectures this week, as well as landslide warnings, leading to the evacuation of hundreds of thousands of people. Models on Thursday indicated that a further 200mm of rain could fall just south of this region as moisture continued to move in from the west.
Two days earlier, Typhoon Saudel had passed through the prefectures of Kagoshima and Okinawa Island, south-west of the mainland, bringing winds of 100mph (160km/h) and extreme rainfall. In the Amami region, 230mm rain fell in a day. The storm was forecast to move into south-east China by the end of the week, with much weaker winds.
While the warm ocean waters surrounding Japan often contribute to increased typhoon activity at this time of year, this year’s developing El Niño could explain why so many storms 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 towards Japan, in El Niño years, the ridge tends to extend northwards, allowing weather fronts to push through more easily and tropical storms developing farther south to “recurve” towards Japan.
Over the past few days, severe convective storms have struck western Europe, particularly the 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 up to 10cm in diameter reported in Catalonia and a significant tornado developing in the village of Pomas, 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.
