The JMA (Japan Meteorology Agency) has a very useful page for checking on flood danger. As you can see in this video, it has an animation function that can help you get a sense of how the situation is changing. Here’s the URL:
http://www.jma.go.jp/en/suigaimesh/flood.html
I was prompted to look at this today because of flood warnings for Fukuoka, to our north. I’ll post a bit more about that in a minute. – Kirk