"A flash flood is very quick flooding of low-lying land, usually without prior warning. It may be caused by heavy rain or water from melted ice or snow" - wikipedia.
The Philippines is a tropical country with no clear dry season. The sun may be scorchingly hot when you go out, but the next hour or so a torrential downpour occurs and you are wet as a whistle. Recent news of tragedies
india flashflood brings car down the river
https://www.youtube.com/watch?v=3H7JgWG5TXo
Bulacan River Tragedy
https://www.youtube.com/watch?v=JHFHxNCqDdM
floodgates opening also cause river accidents
https://www.youtube.com/watch?v=0hl7FNq5PPk