The rainy season began Tuesday in regions from Kyushu to Hokuriku and the Kanto-Koshin area, the Meteorological Agency said the same day.
The only region yet to enter the rainy season is Tohoku. Hokkaido has no rainy season.
In Kyushu, the rains started at about the same time as usual, but in other areas they arrived four to 10 days early. It is the first time since 1951, when rainy season records started being kept, that most of the Japanese archipelago -- ranging from southern Kyushu to the Kanto region -- entered the rainy season at the same time.
Okinawa Prefecture and the Amami Islands in Kagoshima Prefecture entered the rainy season at the beginning of May. A low-pressure system and its seasonal front are running between a high-pressure ridge on the Sea of Okhotsk and a second one over the Pacific Ocean, displaying a typical rainy season atmospheric pattern, the agency said.
Southern Japan will probably have unsettled weather for a week as the rain system remains over the area, the agency added.