Seasons

Japan is generally a rainy country with high humidity. Because of its wide range of latitudes and seasonal winds, Japan has a variety of climates, with a latitude range often compared to that of the east coast of North America, from Nova Scotia to the U. S. state of Georgia. Tokyo is at about 35 degrees north latitude, comparable to that of Tehran, Athens, or Las Vegas. Regional climatic variations range from humid continental in the northern island of Hokkaido, extending down through northern Japan to the Central Highland then blending with and eventually changing to a humid subtropical climate on the Pacific Coast and ultimately bordering very closely on a tropical climate on the Ryukyu Islands. Climate also varies dramatically with altitude and 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, in its elevated position, has hot, humid summers and moderate to short winters with some areas having very heavy snow, and southwestern Japan has long, hot, humid summers and mild winters. The generally humid, temperate climate exhibits marked seasonal variation, such as the blooming of the spring cherry blossoms, the calls of the summer cicada, and fall foliage colors that are celebrated in art and literature.

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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. Annual precipitation averages between 1,000 and 2,500 mm (40 and 100 in). Maximum precipitation, like the rest of East Asia, occurs in the summer months, except on the Sea of Japan coast, where strong northerly winds are at a maximum in late autumn and early winter.

In winter, the Siberian High develops over the Eurasian land mass, and the Aleutian Low develops over the northern Pacific Ocean. The result is a flow of cold air southeastward 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.

Sunshine, in accordance with Japan’s uniformly heavy rainfall, is generally modest in quantity, though no part of Japan consistently receives gloomy fog. Amounts range from about six hours per day on the Inland Sea coast and sheltered parts of the Pacific Coast and Kanto Plain to four hours per day on the Sea of Japan coast of Hokkaido. In December, there is a very pronounced sunshine gradient between the Sea of Japan and Pacific coasts, as the former side can receive less than 30 hours and the Pacific side as much as 180 hours.

As an island nation, Japan has a long coastline. A few prefectures are landlocked: Gunma, Tochigi, Saitama, Nagano, Yamanashi, Gifu, Shiga, and Nara. As Mt. Fuji and the coastal Japanese Alps provide a rain shadow, Nagano and Yamanashi Prefectures receive the least precipitation in Honshu, though this still exceeds 900 mm (35 in) annually. A similar effect is found in Hokkaido, where Okhotsk Subprefecture receives as little as 750 mm (30 in) per year. All other prefectures have coasts on the Pacific Ocean, Sea of Japan, or Seto Inland Sea or have a body of salt water connected to them. Two prefectures, Hokkaido and Okinawa, are composed entirely of islands.

The hottest temperature ever measured in Japan, 41.0°C (105.8°F), occurred in Shimanto, Kochi on August 12, 2013.