After two days of solid rain.
Just throwing this into the mix, an article in 'zakzak' (?) a subsidiary of Fuji media holdings. It's in Japanese and long, so I merely attach it, but it quotes an 'expert' who says that Japanese-US 'intelligence analysts' are seriously considering a DPRK North Korean origin. A similar one was spotted above Kagoshima (in the south of Kyushu) last year, it says.
https://www.zakzak.co.jp/soc/news/20...190005-n1.html
(Video footage on 17 June from a news helicopter at 11,000 meters showed it to be much higher up, with a suggestion of 'in the stratosphere'.)