Japan, South Korea to face more flooding rain in wake of Sepat

By Kristina Pydynowski, AccuWeather senior meteorologist

By Robert Richards, AccuWeather meteorologist

After once-Tropical Storm Sepat grazed southeastern Japan early on Friday, additional rounds of heavy rain will follow and keep the flood risk high across the country and the southern Korean Peninsula for the final days of June.

Sepat was briefly a tropical storm as it grazed the southern coast of Japan on Thursday night. The storm has since lost its tropical characteristics over the open waters of the northern Pacific Ocean.

Attention is now turning toward additional rounds of heavy rain aiming for South Korea and mainland Japan.

"A storm developing along the Mei-yu front will spread heavy rain across parts of Japan through Sunday, local time," said AccuWeather Senior Meteorologist Dave Houk.

The Mei-yu front is a semi-stationary boundary that is draped across southeastern Asia from late spring through the summer and is notorious for triggering torrential rainfall. This torrential rainfall could lead to flash flooding issues given how quickly the rain falls.

There can be widespread rainfall totals of 50-100 mm (2-4 inches) across southern South Korea and western and central Japan through Sunday. In many areas, Houk anticipates that rain to pour down in six to 12 hours.

"With totals up to the AccuWeather Local StormMax™ of 150 mm (6 inches), it will certainly be enough to trigger flooding," he said. "The ground-loosening rains can also cause mudslides."

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Osaka will also face the most persistent downpours on Sunday, the day after the G20 Summit.

"Areas that have been hit with recent rains will be most susceptible to flash flooding and mudslides," Houk added.

Tokyo is expected to escape the heaviest rain and greatest concerns for flooding. Showers, however, can still disrupt weekend plans and may cause minor travel delays.

On the heels of the weekend soaking, AccuWeather meteorologists are monitoring the potential for more heavy rain to threaten southern Japan with flooding and travel disruptions during the first days of July.

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