Heavy downpours to produce significant flood threat across Japan into Saturday

By Faith Eherts, AccuWeather meteorologist
By Eric Leister, AccuWeather senior meteorologist
July 06, 2018, 4:47:47 AM EDT

In the wake of Typhoon Prapiroon, frequent, heavy downpours will continue to inundate a large portion of Japan, increasing the threat of flooding.

"Tropical moisture will surge northward across Japan into this weekend," said AccuWeather Meteorologist Adam Douty. "Heavy downpours are likely, with the heaviest rain falling in Shikoku, Kyushu and central to southern Honshu."

Rainfall associated with Prapiroon inundated Kyushu on Tuesday, dropping nearly 100 mm (3.9 inches) in Tsushima and 60 mm (2.4 inches) in Nagasaki.

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This was followed by widespread rainfall of 50-100 mm (2-4 inches) throughout southern Japan from Wednesday into Thursday.

Flooding in and around Kobe and Kyoto has resulted in more than 1.2 million people being affected by recommended evacuations as of Friday, according to Reuters.

Two lives have been claimed by the weather so far, with several people seriously injured or still missing, having been swept away by flood waters or buried in mudslides.

Additional rounds of downpours will be nearly constant across southern and central Japan into Saturday.

"Through the weekend, rainfall could surpass 250 mm (10 inches) across widespread areas," Douty warned. From Shikoku to central Honshu, 500 mm (20 inches) of rain is possible.

The rate at which this rain will pour down can trigger widespread flash flooding concerns and rapidly bring streams out of their banks. As a result, there can be damage to homes, businesses and crops.

Locations that will be at a high risk for flooding and mudslides include the mountainous areas of Kansai, Chubu and Kanto.

Motorists in these areas will need to stay aware to the threat of blocked or washed-out roads this week. Anyone hiking or camping in the mountains will need to exercise extreme caution as well.

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Travel disruptions could be widespread as well, as roads and railroad tracks become flooded or washed out. Airline delays are also possible due to limited visibility during heavy downpours.

According to Douty, the heaviest rainfall is expected to miss Tokyo. However, residents of Osaka and Nagoya should prepare for disruptive rainfall and flooding into Saturday.

As the downpours wane later in the weekend, attention will turn toward strengthening Maria and any potential threats to Japan.

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