CHIBA - A Level 5 heavy rain emergency warning was issued for more than 20 municipalities in Chiba Prefecture on August 13 after a linear rainband formed over northwestern and southern parts of the prefecture, bringing torrential rainfall exceeding 100 millimeters per hour in several locations and causing widespread flooding, stranded vehicles and damage to buildings.
The linear rainband developed at around 6 p.m., with extremely heavy rain continuing over the same areas for an extended period.
In Matsudo, roads turned into fast-moving torrents of muddy water, creating conditions strong enough to potentially sweep people away.
Flooding was also severe in Ichikawa. At around 5 p.m., roads across a wide area were submerged, with some vehicles stopped after water rose halfway up their bodies. In several places, the road surface was no longer visible in either direction, leaving drivers with few options for escape.
Cars moved slowly through the floodwater, while many others became stranded in the middle of roads.
At one intersection, buses were also unable to move.
Water entered the cabin of a bus traveling through Matsudo, rising close to the seats in the lower section of the vehicle.
One passenger said they had originally been sitting in the lower section of the bus but moved to a higher level after the driver warned that water could enter the vehicle.
"It was a little frightening," the passenger said. "The water was coming in with quite a lot of force."
In Chiba city, drivers were also confronted with sudden walls of spray that temporarily blocked visibility.
Particular concern centered on underpasses and roads beneath elevated structures, where rapidly rising water can trap vehicles.
At one flooded underpass, several people tried to push a stranded vehicle to safety, but the water had risen above waist height, making the effort extremely difficult.
Despite the conditions, other vehicles were seen continuing into the underpass.
Weather radar showed intense rain developing around Chiba Prefecture from about 3 p.m. and remaining over the same locations for hours.
Emergency alerts for record-breaking short-term rainfall were issued in numerous areas, including Chiba, Kashiwa and Yachiyo, where hourly rainfall exceeded 100 millimeters.
Shortly after 6 p.m., flooding was visible behind the Chiba Prefectural Police headquarters.
Elsewhere in Chiba city, water surged upward from multiple manholes as drainage systems struggled to cope with the volume of rain.
Near Kashiwa Station, water was seen shooting higher than vehicles, while floodwater entered a fast-food restaurant.
By shortly after 7:30 p.m., Level 5 heavy rain emergency warnings covered a wide area of Chiba Prefecture.
The Japan Meteorological Agency issued the highest-level warning for municipalities in northwestern Chiba, including Chiba and Ichikawa.
An agency official said there was an extremely high probability that some form of disaster had already occurred and warned that Level 5 conditions could be declared in additional municipalities.
The official also stressed that waiting for a special warning before evacuating could be too late.
The downpour struck during the evening rush hour, disrupting transportation and leaving long lines at bus stops.
One line stretched an estimated 20 to 30 meters.
A person waiting for a taxi said a train journey that normally took about 20 minutes from Oshiage had taken more than an hour and that there was no clear indication of how much longer it would take to get home.
Another traveler returning from Tokyo Disneyland said trains were no longer operating. The person said lightning had been intense around Maihama and expressed concern about whether they would be able to return home, as well as the possibility of lightning-related power outages.
Flooding continued to affect Ichikawa, where abandoned vehicles remained on inundated roads and businesses placed wooden boards outside entrances in an attempt to stop water from entering.
One bar reported that floodwater had entered the premises after rain continued from the evening.
A staff member said the interior had become soaked and pointed to damage extending roughly 15 to 20 centimeters up the wallpaper.
The business also temporarily lost electricity after its circuit breaker tripped.
The staff member said passing vehicles worsened the flooding by creating waves on roads that had effectively turned into rivers, forcing additional water into the building.
The severe weather was not limited to Chiba Prefecture.
In Oyama, Tochigi Prefecture, hourly rainfall reached 51.0 millimeters shortly after noon, while Saitama recorded 53.0 millimeters in an hour shortly after 3:30 p.m.
In Atsugi, Kanagawa Prefecture, blue skies were still visible shortly after 1:30 p.m., but conditions changed dramatically about 20 minutes later as heavy rain reduced visibility and motorists switched on their headlights.
At a leisure facility crowded with visitors during the Obon holiday period, people who had been outdoors moved under covered areas to shelter from the rain, while strong winds also swept through the site because of its proximity to the sea.
Source: TBS
