Some of the best times to travel to Hawaii are during early summer, winter months and the beginning of the school year. During these times the weather in Hawaii is beautiful, and the island is usually less crowded.
In mid-June to mid-July, American students start summer school, so less people are in Hawaii. In the winter, Hawaii still has beautiful weather compared to the East Coast. In the beginning of the school year, around August and September, most students start school, and fewer people visit Hawaii.
The worst times to travel to Hawaii are the last weeks of April and early May, which is known as the "Golden Week" in Japan. During this time, Japanese workers get a week off from work, so they head in droves to Hawaii. Other bad times are early October and December when Hawaii hosts the Honolulu Marathon and Ironman Triathlon World Championships.