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Climatological dates of Baiu onset and withdrawal in each district of Japan

The Baiu is a cloudy and rainy period of early summer in Japan. All areas except the country's northernmost island, Hokkaido, experience this rainy season, which lasts from early June to late July. In Okinawa/Amami (the southernmost part of the Japanese Archipelago), the Baiu starts and ends about a month earlier than elsewhere.

The period of the Baiu is operationally identified by the Japan Meteorological Agency (JMA) for each year and for 12 areas. JMA has been trying to identify a transition period of about five days for the start and end of the Baiu, although this is by nature a challenging task in some cases. The climatological date (from the average of data covering the period 1991-2020) at the center of each transition period is shown in the table below.

District Climatological date of Baiu onset Climatological date of Baiu withdrawal
Okinawa around 10 May around 21 June
Amami around 12 May around 29 June
Kyushu (South) around 30 May around 15 July
Kyushu (North) around 4 June around 19 July
Shikoku around 5 June around 17 July
Chugoku around 6 June around 19 July
Kinki around 6 June around 19 July
Tokai around 6 June around 19 July
Kanto/Koshin around 7 June around 19 July
Hokuriku around 11 June around 23 July
Tohoku (South) around 12 June around 24 July
Tohoku (North) around 15 June around 28 July