Rainy season officially starts at some part of Japan

The rainy season, usually called " plum rain season," has started Thursday in Japan's Kanto region including the Tokyo Metropolitan area as well as Hokuriku region in central Japan facing the Sea of Japan, local media reported.

Compared with data of an average year, the rainy season arrived three days earlier in Kanto region and seven days earlier in Hokuriku region, said the Japan Meteorological Agency.

The agency also warned of possible heavy rain on the Pacific coast of eastern Japan through Friday.

In most of Japan, the rainy season lasts from the beginning of June to mid-July, while it affects the islands of Okinawa about one month earlier. Only Japan's northern most main island of Hokkaido gets barely affected by the rainy season.

It is caused by the collision of cold northerly and warm southerly air masses, which results in a relatively stable bad weather front over the Japanese archipelago for several weeks.