Weather tracker: Extreme rainfall deluges Japan and South Korea

Downpours break records and cause transport chaos, evacuations and deaths, as people get trapped inside vehicles

South Korea and Japan were hit by extreme rain late last week and into this week. On 13 August in the city of Chiba near Tokyo there was a record-breaking 115mm of rainfall in just one hour, while the nearby city of Sakura broke its own record with 97mm in one hour. Local authorities issued a level 5 emergency warning for heavy rain, the highest alert level and the first time one has been issued since the system was implemented in May.

More than 100,000 households were asked to evacuate, with more than 20,000 in the Chiba prefecture left without power, while thousands of people were stranded at Tokyo’s Narita airport. Thirteen people have been confirmed dead, at least three of whom were found trapped inside their vehicles. One person is still missing.

Japan is no stranger to heavy rainfall, thanks to the conditions created when warm and moist air from the north Pacific meets cooler air. This latest event has been especially severe, however, with the Japan Meteorological Agency describing it as an “unprecedented level” of heavy rain. There was also record-breaking rain in nearby South Korea , where in the city of Geoje 124.5mm fell within one hour early on 17 August. In total more than 400mm fell through the night.

Meanwhile, across the north Pacific, Hurricane Lala achieved category 1 hurricane status on 15 August, travelling westwards towards Hawaii with wind speeds of about 80mph (130km/h). Lala passed just to the south of the island chain the following day, with the eyewall grazing the southern part of the main island, causing it to weaken back down to a tropical storm. Kona international airport on the island recorded its lowest ever pressure as Lala passed. After passing Hawaii, the storm restrengthened into a category 4 hurricane and gradually shifted to a more northerly trajectory. It is not expected to affect any other Pacific Islands before degrading.

Another system in the north Pacific developed close to Micronesia last week and was named Saudel as it reached tropical storm status. Saudel is forecast to intensify through the weekend, becoming a very strong or potentially violent typhoon. Travelling north-west, it will pass very close to or even make landfall on the Northern Mariana Islands, where a warning is already in place. Next week, Saudel is expected to track towards Okinawa prefecture, the chain of islands to the south of mainland Japan .