Japan comprises a group of islands off the east coast of Asia. From north to south the main islands are Hokkaido, Honshu, Shikoku and Kyushu. All are hilly or even mountainous, particularly Honshu where the highest peaks (e.g. Fujiyama) are over 12,000 feet. There are numerous other peaks (some volcanic) over 6,500 feet, and the higher ones on Hokkaido and Honshu are snow covered all year round.
The climate of Japan is heavily influenced by the great seasonal wind reversal of the Asian monsoon, but there are significant differences between (say) north China and Japan. The Japanese islands have a climate modified and moderated by the sea. Winters are less cold than those in the same latitude on the continent and precipitation is much heavier. Winter precipitation is particularly heavy on the west coasts of Hokkaido and Honshu. Snowfall here is heavy as the cold, outblowing winter monsoon from Siberia and Manchuria is warmed and picks up moisture over the sea. Elsewhere in Japan, winter is a relatively drier season.
In summer and early autumn much of the heavy rain is brought by typhoons, or tropical cyclones which move north from the South China Sea or the region east of the Philippines. In some parts of central and southern Japan there is a double rainfall maximum; one in early summer (the so-called Bai-U or plum rains) and a second in late summer or early autumn, brought by typhoons.
North Japanese winters are severe (especially in Hokkaido) with heavy snowfall. In the south of Honshu and in the other two islands the winters are mild and almost subtropical, particularly around the coasts of the Inland Sea (the stretch of water between Shikoku and Kyushu). Winter rainfall is light here and frosts are very rare.
In northern Japan, summers are short but warm, and on the eastern coasts the summers are wetter than winter. In central and southern Japan the summers are very warm but excessively hot days are rare. Because Japan is dominated by moist maritime air at this time with frequent cloud, the summer heat is often oppressive and sultry, particularly in the cities.
In the mountains temperatures are sufficiently reduced by altitude as to be very pleasant in summer, and on sunny spring and summer days, conditions can be quite delightful.
In most parts of Japan, the daily sunshine amounts are only moderate because of the abundant rain and humid atmosphere. They are lowest in Hokkaido and northern Honshu, where they average from two to three hours a day in winter to five or six hours a day in summer. Farther south there is more sunshine with an average of six to seven hours a day throughout the year. Spring is probably the most pleasant season in Japan, the weather being usually warm and sunny, but fresher and drier than summer or autumn.