Japan Data

Japan’s Rainy Season Brings Risk of Torrential Downpours


Rainfall can vary considerably from year to year in Japan’s rainy season, but heavy downpours may cause serious landslides and flooding.

On May 4, Japan’s rainy season started in Okinawa and one week later, on May 11, in Amami Ōshima. June will see this gloomy weather continue to the north of Kyūshū (excluding Hokkaidō). The highest caution is needed at the latter end of the rainy season when torrential downpours can lead to landslides and flooding of rivers. On July 3 last year, a large-scale mudslide occurred in Atami, Shizuoka Prefecture, killing more than 20 people.

The chart below shows the dates the rainy season started in various regions in 2021 as well as the average starting and ending dates. Last year the rainy season came early to Northern Kyūshū, Southern Kyūshū, Shikoku, and Chūgoku, starting from mid-May and continuing for more than two months.

2021 Rainy Season Dates and Average Annual Dates

Start of Rainy Season 2021
(Average Starting Date)
End of Rainy Season 2021
(Average Ending Date)
Okinawa May 5
(May 10)
July 3
(June 21)
Amami Ōshima May 5
(May 12)
July 3
(June 29)
Southern Kyūshū May 11
(May 30)
July 11
(July 15)
Northern Kyūshū May 11
(June 4)
July 13
(July 19)
Shikoku May 12
(June 5)
July 19
(July 17)
Chūgoku May 12
(June 6)
July 13
(July 19)
Kansai June 12
(June 6)
July 17
(July 19)
Tōkai June 13
(June 6)
July 17
(July 19)
Kantō Kōshin June 14
(June 7)
July 16
(July 19)
Hokuriku June 13
(June 11)
July 14
(July 23)
Southern Tōhoku June 19
(June 12)
July 16
(July 24)
Northern Tōhoku June 19
(June 15)
July 16
(July 28)

Created by Nippon.com based on data from the Japan Meteorological Agency.

In an average year, the rainy season starts from early June in cities like Fukuoka, Osaka, Nagoya, and Tokyo from Northern Kyūshū through to Kantō Kōshin, and ends around July 20. The amount of precipitation during this time is around 500 to 600 millimeters in Northern Kyūshū and 300 millimeters in Kantō Kōshin and Tōkai.

Rainfall Varies Year to Year

The average rainfall during the rainy season over the past thirty years in Kantō Kōshin can be seen in the following chart. The figures vary considerably year to year and there are some cases like in 1990 when there was a dry rainy season with only half the average annual rainfall recorded that year. In contrast to this, the 2020 rainy season ended late on August 1 and had 1.7 times the usual rainfall.

(Originally published in Japanese. Banner photo © Pixta.)

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