Intellicast's Climate Guide To Japan

This beautiful, mountainous island nation is a little larger than Great Britain, with a varied climate not unlike that of the eastern United States. The main islands are situated from north to south - Hokkaido, Honshu, Shikoku and Kyushu. Each island is mountainous with many volcanic peaks, some still very active. Honshu, the largest island, is especially mountainous with the largest mountain, Mount Fujiyama (often called Fuji), rising to over 12,000 feet. Some of these mountains remain snow-covered all year long.

The northern island, Hokkaido has a climate like the northeastern United States with frigid temperatures, limited sunshine and heavy snows in winter and a relatively short but warm summer. The southern islands, Shikoku and Kyushu, on the other hand, have a mild, almost subtropical climate similar to the Southeast Coast of the United States.

The four components that determine Japan's climate are the seasonal wind reversals of the Asian monsoon; the modifying effect of the surrounding water; the effect from varied, mountainous terrain; and the country's position in the path of many tropical storm systems during the summer and fall.

WINTER
Most years, the winter monsoon regime begins by November. Winds blow off the continent carrying cold and dry polar air with them. In the short trip across the Sea of Japan, the cold air modifies and picks up moisture that is deposited on the islands, especially over the windward slopes. Snowfall of over 200 inches a year occurs in some locations on the northern islands. Elsewhere, winter is the driest season. Most of the precipitation comes from storms, which form from time-to-time along the leading edge of the polar air and bring general rains and mountain snows to the islands.

SPRING
Spring is the most pleasant season in Japan, not only for the beauty of the flowering trees, gardens and countryside, but also for the most delightful weather. Though spring showers are to be expected, the springs tend to be drier and sunnier than summer and fall, and temperatures are very pleasant even in the mountains.

SUMMER
Summer tends to be cloudier than the spring. During the summer monsoon, the winds turn from off-the-continent to off-the-sea. With the onset of the monsoon, heavy rains can occur in the southern islands. Later on in the summer, tropical storms and typhoons, moving from the South China Sea or the Western Tropical Pacific increase the threat of heavy rains and sometimes damaging winds. In between these bigger systems, sultry and even oppressive summer weather prevails in the major cities like Tokyo. Relief can be found in the higher elevations, which are popular retreats during the heat of summer.

FALL
Storms from the Tropics are the main concern in the early fall through October even as the air cools. By the end of October the temperatures are already down 20 degrees (F) from the summer peak. By November, the Tropics begin to quiet down and the winter monsoon season begins.

Month
Record Low
Normal Low Normal High Record High Average # Rain Days Average Rainfall
January 17°F -8°C
29°F -2°C
47°F 8°C
72°F 22°C
5 1.9 inches 48 mm
February 18°F -8°C
31°F -1°C
48°F 9°C
77°F 25°C
6

2.9 inches 74 mm

March 22°F -6°C
36°F 2°C
54°F 12°C
77°F 25°C
10 4.2 inches 107 mm
April 30°F 11°C
46°F 8°C
63°F 17°C
85°F 29°C
10 5.3 inches 135 mm
May 36°F 2°C
54°F 12°C
71°F 22°C
88°F 31°C
10 5.8 inches 147 mm
June 47°F 8°C
63°F 17°C
76°F 24°C
93°F 34°C
12 6.5 inches 165 mm
July
55°F 13°C
70°F 21°C
83°F 28°C
99°F 34°C
10 5.6 inches 142 mm
August 60°F 16°C
72°F 22°C
86°F 30°C
101°F 38°C
9 6.0 inches 152 mm
September 51°F 11°C
66°F 19°C
79°F 26°C
96°F 36°C
12 9.2 inches 234 mm
October 36°F 2°C
55°F 13°C
69°F 21°C
90°F 32°C
11 8.2 inches 208 mm
November 26°F -3°C
43°F 6°C
60°F 16°C
81°F 27°C
7 3.8 inches 97 mm
December 30°F -7°C
33°F 1°C
52°F 11°C
74°F 23°C
5 2.2 inches 56 mm
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