Atmospheric conditions are becoming extremely unstable in the Kanto-Koshin region. Radar analysis shows some parts of Chiba Prefecture received more than 100 millimeters of rain in one hour on Friday morning.
Japan's weather agency says Yun-yeung is over Pacific waters, south-southwest of Omaezaki City in Shizuoka Prefecture, and moving north.
Strong rain prompted a mudslide alert to be issued for some parts of Chiba and Ibaraki prefectures as well as the Izu Islands.
Some rivers have exceeded the flood danger level in Chiba Prefecture.
Torrential rain fell in Chiba Prefecture. Radar analysis shows that about 100 to 120 millimeters of rain fell in one hour on Friday morning in Kimitsu City and Katsuura City. In the six hours up to 11 a.m., 246 millimeters of rain fell in Kamogawa City and 219.5 millimeters fell in Mobara City. Both figures exceeded the average rainfall for the entire month of September and are the highest since record-keeping began.
The total rainfall for the 24-hour period through Saturday noon could reach 250 millimeters in the Kanto-Koshin region, 150 millimeters in Tohoku, 120 millimeters in Tokai, and 100 millimeters in the Izu Islands.
Weather officials are calling on people to watch out for mudslides, flooding and swollen rivers — as well as strong winds, high waves, lightning and gusty winds.
Shinjuku Station swamped
Leaking water drenched an underground passage at Shinjuku Station, Tokyo's busiest, on Friday morning.
Water that poured from the ceiling flooded about 15 meters of walkway during the busy morning rush hour. There were no major disruptions to commuters.
Some suspended transportation services in Kanto region resume operations
The storm is affecting some public transportation services in the Kanto region.
JR East Japan Railway says the Tokaido Line, the Ito Line and the Ome Line resumed services at around 1 p.m.
Operations on the entire Kururi Line have been canceled.
JR East is asking people to check the latest information on its website.
Shinkansen services are operating normally.
Some flights to and from Tokyo's Haneda Airport have been disrupted.
As of 1 p.m., Japan Airlines has canceled 17 flights, while All Nippon Airways has canceled 12. Star Flyer has canceled 3 flights.