East Asian rainy season

Monsoon season in East Asia

The East Asian rainy season , also called the plum rain, is caused by precipitation along a persistent stationary front known as the Meiyu front for nearly two months during the late spring and early summer in East Asia between mainland 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. These weather systems can produce heavy rainfall and flooding.

In China, the term "plum rain" was used for the rain in the fourth and fifth lunar month. It specifically refers to the historical belief that, when the plums turn yellow and fall at the south of the Yangtze in the fourth and fifth months, the moisture that evaporates from the plant turns into rain.</poem>

Japan later adapted and transliterated the Chinese term "plum rain" to call the rainy season (梅雨). The season is instead commonly called Jangma (장마) in Korea, which means "long rain". The term was originally spelled Dyangmah (댱맣) in 1500s, which was the mix of the hanja character 長 ("long") and the old native Korean word 맣 (mah, "rain"). The word Dyangmah eventually transformed from Jyangma (쟝마) in 1700s to the current form of Jangma after the 1900s.

An east west zone of disturbed weather during spring along this front stretches from the east China coast, initially across Taiwan and Okinawa, later, when it has shifted to the north, eastward into the southern peninsula of South Korea and Japan. In Taiwan and Okinawa, the rainy season usually lasts from May to June. In Russian Primorsky Krai, Japan, and Korea, it lasts from June to July (approximately 50 days). In eastern China (especially the Yangtze and Huai River regions), it lasts from July to August. The weather front forms when the moist air over the Pacific meets the cooler continental air mass. The front and the formation of frontal depressions along it brings precipitation to Primorsky Krai, Japan, Korea, eastern China, and Taiwan. As the front moves back and forth depending on the strength of cool and warm air masses, there is often prolonged precipitation and sometimes flooding in eastern China. However, in the years that it does not rain as much as usual, a drought might result. The rainy season ends when the warm air mass associated with the subtropical ridge is strong enough to push the front north and away.

The high humidity in the air during this season encourages the formation of mold and rot not only on food but on fabrics as well. Environmentally, heavy rains encourage mudslides and flooding in all areas affected. The most rain in a one hour period as recorded in Japan was in Nagasaki in 1982 with The highest overall recorded rainfall during the rainy season in Japan was in 2003 when Miyazaki Prefecture recorded rains of .

In Japan, the rainy season is called (梅雨), and lasts from early June to mid July in most of the country (Honshu, Kyushu and Shikoku), approximately June 7 to July 20 in the Kansai and Kantō regions in Honshū. The season is roughly a month earlier (early May through mid June) in Okinawa (the southernmost region of the country). There is no pronounced season in Hokkaidō (the northernmost region of the country) because the front usually attenuates before it reaches the region so that it cannot produce the abundant rainfall. is also known as literally "the fifth month rain (in the Lunisolar calendar; Japanese traditional calendar)", roughly corresponding to June in the modern calendar; 五月雨. The pop artist Eiichi Ohtaki produced a popular song by this name, and a Second World War Japanese naval ship was also given this name. The rains in the middle of November early December are sometimes called the , literally "rainy season of the camellia" on account of the timing with the blossoming of the seasonal flower. This period is generally avoided for tourism, but some sights are considered particularly atmospheric in the rain and fog, particularly mountain forests, notably Sacred Sites and Pilgrimage Routes in the Kii Mountain Range (including Mount Kōya).