Record-breaking downpours in Chiba Prefecture in the Tokyo metropolitan area left four people dead and one missing, among other casualties. With railways and roads cut off in many places, about 7,000 people were stranded overnight at Narita Airport.
According to Kyodo News and NHK on the 14th, Chiba Prefecture said that as of the morning, there were four deaths, one missing person, and one person in cardiac arrest due to the heavy rain that continued from the previous day.
Since the afternoon of the 13th, more than 100 mm of rain per hour has fallen on Chiba Prefecture. In Chiba, 348 mm of rain fell over 12 hours until 1:40 a.m. that day. It was the most precipitation since weather observations began and is about three times the average rainfall for August.
At an observation station in Midori Ward, Chiba, about 450 mm of rain was recorded over six hours from 6 p.m. on the 13th. The Japan Meteorological Agency issued a level 5 heavy rain emergency warning, the highest disaster alert, for parts of Chiba Prefecture.
The deluge also paralyzed transportation in the metropolitan area. Operations were suspended on some lines of JR East and Keisei Electric Railway, and restrictions were imposed on sections of expressways.
At Narita Airport, with train and bus services disrupted, about 7,000 passengers were stranded at the airport as of 4 a.m. on the 14th. Airport authorities provided them with water, food, and sleeping bags.
Chiba Prefecture opened 17 facilities, including the prefectural office and Makuhari Messe, as temporary shelters for residents and travelers who could not return home. According to local media, about 3,900 people spent the night at these facilities, and the number of people across Chiba Prefecture who were unable to return home reportedly reached 10,000.
The heavy rain was analyzed to have occurred as humid air flowing along a high-pressure system collided with cold air aloft, after Typhoon No. 15 "Chan-hom" weakened into a tropical depression but left abundant moisture. Near Chiba Prefecture, easterly and northerly winds collided, causing strong rain clouds to develop repeatedly.
The Japan Meteorological Agency lifted the level 5 emergency warning, the highest level, and lowered the alert, but urged continued caution, saying that in areas already drenched, the risks of landslides, river flooding, and inundation of low-lying areas remain.