The Japanese archipelago's weather is rather unpredictable, so accurate yearly weather forecasting is really not possible. The predictions below for sunny and cloudy periods, and when shooting outdoors in metropolitan Tokyo is possible, are rough. The Meteorological Bureau (and commercial weather forecasting offices) are fairly accurate up to week in advance. If you have a coordinator who understands Japanese, call (81-3) 3540-3700 for a recording of the weekly weather forecast.
English Weather Services
For about a month and a half during June and July, the expectancy of rain is very high, around 80%.
There is little chance of sunshine. Halfway through the rainy season, there may be a day here or there of sunshine.
Don't think the rainy season is over until the Weather Bureau announces the rain front has passed.
Average period of RAINY SEASON (data from 1961 - '90 )
TOKYO : June 9th - July 20th
Typhoons are likely to spawn around the equator in mid June, head north through the Philippines, Taiwan etc., and strike Japan from September through mid October. Out of an average of 15 - 20 typhoons spawned each year, an average of 5 strike Japan. Early typhoons move from the south, and their path usually is up the Sea of Japan (west of Japan). As the season progresses, the paths move more and more easterly. Most often, they do not in fact strike Tokyo.
MIDDLE TO THE END OF MAY. If it rains, it doesn't last more than a few days. The temperature is bearable, humidity is low, flowers are in bloom and the leaves are green. Avoid "Golden Week" holidays, the first week, when most businesses are closed.
END OF JULY TO THE END OF AUGUST. Nature is at its best, but people not used to the climate wilt. For two weeks from around the 10th of August, business slows down for Obon holidays. Warning: it gets hot and very muggy, and you should expect evening showers.
BEGINNING OF NOVEMBER THROUGH THE END OF FEBRUARY. It rains very little in Tokyo during the winter, and only rarely snows. Dress warmly at night and at the peak of winter. The sky is sometimes clouded over, and nature's colors are faded. Like most countries, New Years might best be avoided, unless you've made arrangements to shoot festivities in advance, as businesses slow down and close. Warning: there is no daylight savings time in Japan, so it gets dark as early as 4:30. Get an early start!