Tokyo: Strategies: When to Go
A no-brainer. Cherry-blossom time, in the early spring, is the absolute best moment to see Tokyo, when its public parks are covered in the delicate pink leaves. The cherry trees usually bloom in March, but the precise date is as ephemeral as nature. Office workers take their picnic lunches to the parks to marvel at the beauty everywhere; amateur painters are out in force, trying to capture the scene. Fall, when the trees are a riot of orange and brown, is also a superb time to come. Summer can be uncomfortably hot, and winter is chilly.
— Mark Graham 04/06/2008