Japan is generally a rainy country with high humidity. Because of its wide range of latitude, Japan has a variety of climates, with a range often compared to that of the east coast of North America, from Nova Scotia to Georgia. Tokyo is at about 36 north latitude, comparable to that of Tehran, Athens, or Los Angeles. The generally humid, temperate climate exhibits marked seasonal variation celebrated in art and literature, as well as regional variations ranging from cool in Hokkaido to subtropical in Kyushu. Climate also varies with altitude and with location on the Pacific Ocean or on the Sea of Japan. Northern Japan has warm summers but long, cold winters with heavy snow. Central Japan has hot, humid summers and short winters, and southwestern Japan has long, hot, humid summers and mild winters.

Two primary factors influence Japan's climate: a location near the Asian continent and the existence of major oceanic currents. The climate from June to September is marked by hot, wet weather brought by tropical airflows from the Pacific Ocean and Southeast Asia. These airflows are full of moisture and deposit substantial amounts of rain when they reach land. There is a marked rainy season, beginning in early June and continuing for about a month. It is followed by hot, sticky weather. Five or six typhoons pass over or near Japan every year from early August to early September, sometimes resulting in significant damage. Annual precipitation, which averages between 100 and 200 centimeters, is concentrated in the period between June and September. In fact, 70 to 80 percent of the annual precipitation falls during this period. In winter, a high-pressure area develops over Siberia, and a low-pressure area develops over the northern Pacific Ocean. The result is a flow of cold air eastward across Japan that brings freezing temperatures and heavy snowfalls to the central mountain ranges facing the Sea of Japan, but clear skies to areas fronting on the Pacific.

Two major ocean currents affect this climatic pattern: the warm Kuroshio Current (Black Current; also known as the Japan Current); and the cold Oyashio Current (Parent Current; also known as the Okhotsk Current). The Kuroshio Current flows northward on the Pacific side of Japan and warms areas as far north as Tokyo; a small branch, the Tsushima Current, flows up the Sea of Japan side. The Oyashio Current, which abounds in plankton beneficial to coldwater fish, flows southward along the northern Pacific, cooling adjacent coastal areas. The meeting point of these currents at 36 north latitude is a bountiful fishing ground.

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Source: U.S. Library of Congress