The East Asian rainy season, commonly called the plum rain (Chinese and Japanese: 梅雨; pinyin: méiyǔ; rōmaji: tsuyu/baiu; Korean: 장마; romaja: jangma; Russian: затяжные, zatyazhnie), is caused by precipitation along a persistent stationary front known as the Mei-Yu front for nearly two months during the late spring and early summer between eastern Russia, China, Taiwan, Korea, and Japan. The wet season ends during the summer when the subtropical ridge becomes strong enough to push this front north of the region.
During our trip from 30 May to 6 June, we experienced Meiyu from 2 June to 4 June. The 4 diagrams below shows our location during the Meiyu. We were lucky to have escaped the wrath of the rain.
The details can be found here: http://nicoledebond.com/monsoons/