With Hawaii, there’s not any dramatic changes in climate throughout the seasons, because every island has a wet and a dry side, anyway. It will be slightly cooler in winter, but that’s pretty negligible: bring a sweatshirt or light pullover for evenings.
Instead, Laurel continues, it’s more helpful to scope the ocean:
The biggest issue you’ll face if you visit Hawaii in fall/winter (Sept. to about April) is big surf, which can prevent you from participating in certain activities or visiting specific areas. If you want to explore Kauai’s Na Pali Coast by Zodiac or hike the Kalalau Trail, you’ll be unable to do so during those months.
If you’re contemplating any activity like sea-kayaking, windsurfing, or Zodiac trips, be sure to check with outfitters on when trips run, and if there’s an off-season. The same goes for surfing; if you’re not at an expert level, you may want to save it for the summer, or at least plan what part of the island has smaller surf in the winter months.
I’d say the best time to visit Hawaii is in May or June. I like these months mostly because they’re right before tourist season kicks into full-swing, and the weather is gorgeous. If you search online you can usually find some great deals on tickets as well.
Come September-December most parts of Hawaii are cloudy (particularly the windward side), and it can be a bit rainy as well.
I’ve spent time on Maui in mid-February and Oahu in mid-December. Every day was sun and mid-80s temps.
I arrived in Honolulu during the marathon, so it was a bit crowded…not really a bad kind of crowded, though. But I concur with Laurel, re: big surf. My family and I drove up to the North Shore for the Reef Hawaiin Pro surf competition, but it was canceled for the day on account of unruly waves.
Other than that, I had 0 complaints.
So, what’s the best time to visit Hawaii?
Short answer: January to June. That’s a lot of high-season.
For something a little different, check out David Page’s Notes on the Other Side of Hawaii.