It is the baiu season for Nansei Islands such as Okinawa and it is often seen when the baiu front in the vicinity of Nansei Islands goes up to the north temporarily along the south coast of Honshu.
沖縄など南西諸島の梅雨期にあり、南西諸島付近にある梅雨前線が一時的に本州南岸沿いに北上したときに多く見られる。