*雨雲レーダー (rain cloud radar) comes with Yahoo! 天気 app is also useful.
I love rain, snow, and even typhoon, meaning all types of natural phenomenon in Japan since my childhood, except for the earthquake, lightning, and tsunami.
However, the rain we were experiencing since the early evening yesterday is quite abnormal and dangerous. First, the rain clouds look massive, covering up almost a Western half of Japan. Second, there is no sign of it to stop at all by this evening (6th July), and the news has been reporting all the time the latest forecast and evacuation information since morning. The government's disaster control department has issued "大雨特別警報 (O-ame Tokubetsu Keiho: Emergency Warning for Heavy Rain)" in Fukuoka, Saga, Nagasaki, Hiroshima, Hyogo, Kyoto and other prefectures. It is the most critical warning issued when people in the impacted region(s) should be extremely alarmed for the forecast of the rain, which is as heavy as that could occur once in several decades. Everyone in the affected area must prepare for evacuation and other acts that should save own life.
My heart goes to the people in Osaka, who suffered from the massive earthquake and aftershocks since 18th June. The cloudburst today is causing another impact on those who have been evacuating since then.
When the Emergency Warning was issued in the morning, my Google Pixel 2 bought in India sounded a high-tone buzzer released by Yahoo! disaster alert app. However, the pop-up alert and the subsequent page after clicking it were all written in Japanese. When most of the interfaces of Japanese apps automatically detect the language setting of my Google Pixel (English,) why does the Yahoo! Disaster Alert (防災速報) app, which is playing a vital role in people's daily lives here in Japan, seem to be only in Japanese? I feel it's bizarre.
Anyway, I still recommend you to install this Yahoo! app when you are visiting Japan so you can receive push warnings regarding the possible disaster and other updates of the ever-fast changing weather situation in the country.
Yahoo! 防災速報 (Disaster Alert) app
And when you receive an alert from the app, which is likely to be in the Japanese language, I guess you know what to do; I am describing it, though, for who may need (Android version.)
*The following steps are for Android Smartphones.

The app will look like this when you received a pop-up alert (warning.)
Take a screenshot.

Start Google Photo gallery, open the desired screenshot.
Touch the ”Lens” icon.

Touch "Text selection."

Select the desired text and touch "TRANSLATE."

*However, observe your surrounding carefully
and try to keep connected with the people around you;
that is the best disaster handling measure.