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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 1981-2010) 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 9 May around 23 June
Amami around 11 May around 29 June
Kyushu (South) around 31 May around 14 July
Kyushu (North) around 5 June around 19 July
Shikoku around 5 June around 18 July
Chugoku around 7 June around 21 July
Kinki around 7 June around 21 July
Tokai around 8 June around 21 July
Kanto/Koshin around 8 June around 21 July
Hokuriku around 12 June around 24 July
Tohoku (South) around 12 June around 25 July
Tohoku (North) around 14 June around 28 July