First off and during in late June to mid-July 2018 had successive heavy downpours in southwestern Japan. In addition, these downpours resulted in widespread, devastating floods and mudflows. The event is officially being called 平成 30 年7月豪雨.

As well, another term is a guerrilla rainstorm or (ゲリラ豪雨 gerira gō’u) a Japanese expression. All used to describe a short, localized downpours.

Therefore that’s of over 100mm of rain per hour. In addition and all caused by the unpredictable formation of cumulonimbus cloud. The term is often used by the Japanese media in reporting such events, but does not have an official meaning nor is it used by the Japan Meteorological Agency.

Koji Sunomori
Koji Sunomori

Therefore the heavy rain in July 2018, Heisei 30 by the Japan Meteorological Agency.  So as July 13, 209 were reported dead from this rain. More importantly over 8 million people were advised or urged to evacuate. About  54,000 members of the Japan Self-Defense Forces, police and firefighters were searching for the people trapped or injured in landslides and flooding. More noteworthy, all triggered by the heavy rain. This is while the Japanese government has set up a liaison unit at the crisis management center. A center of the Prime Minister’s Office to gather all the information.

CNN reported:

Worst part, Koji Sunomori couldn’t see the boy’s face. Although he knew the lifeless body belonged to his 2-year-old stepson, Kenta. As well as he was wearing his favorite baseball shirt.

Furthermore, Sunomori found him among the rubble. Rubble of what was supposed to be his new home. The 54-year-old had just married his wife, Nana, last month, and was planning to move in with her and her two children from a previous marriage in the coming days.

CNN further reported:
Experts say the floods inflicted so much damage — and so many deaths — because a unique set of weather conditions led to a massive amount of rain pummeling an area not prepared for it.
The rain hit a mountainous region, which meant the water picked up speed as it flowed down. The areas hit by those waters were, like much of rural Japan, home to an elderly population who cannot evacuate easily.
“When it’s a sudden onset event, you don’t have time for people to get out of the way,” said Doug Bausch, a science adviser at the Pacific Disaster Center, an consultancy that works in disaster risk management.
This aerial image shows the destroyed iron bridge of JR Geibi Line due to  torrential rains in Hiroshima.
This aerial image shows the destroyed iron bridge of JR Geibi Line due to torrential rains in Hiroshima.
Further info on CNN