Heavy Rain, Flood Threat for Tokyo

Several rounds of rain will cross Japan early this week, leading to the threat of flooding in southern parts of the country.

Cities from Nagoya to Tokyo will be at the greatest risk for heavy rainfall as an unusually strong trough of low pressure pulls moisture northward from the Philippines Sea.

While the heaviest rain and greatest threat for flooding will occur across southeastern Honshu, several days of clouds and rain will lead to travel delays in the air and on the ground across much of the country.

Along the southeastern coast of Honshu, from Nagoya to Tokyo, rainfall totals from Monday into Tuesday are expected to be 25-75 mm (1-3 inches) with a few locations seeing upwards of 150 mm (6 inches). The heaviest rain is most likely in the mountains between these cities.

Rounds of heavy rain in urban areas will lead to the risk for flash flooding in low-lying areas. Snowmelt from the higher terrain in the Japanese Alps can also exacerbate the flooding concern in mountain river valleys.

While flooding will be the greatest risk associated with heavy rain, there will also be an elevated risk for mudslides in the mountainous terrain of southern Honshu.

Across the rest of Japan and into South Korea, flooding will not be a great concern, but rain over the course of several days can lead to lengthy travel delays.

This same disturbance will also bring showers to eastern China, including to Shanghai later Sunday and into Monday. The Formula 1 Chinese Grand Prix is being held in Shanghai on Sunday, scheduled to start 2 p.m., local time. With the threat for rain not arriving until late in the day, the race is expected to remain dry.

Eastern China will dry out through the middle of the week, but areas of rain are expected to linger in Japan. The heaviest of the rain, however, will have exited the country.