Most visitors don't come to Hawaii when the weather's best in the islands; rather, they come when it's at its worst everywhere else. Thus, the high season -- when prices are up and resorts are often booked to capacity -- is generally from mid-December through March or mid-April. The last 2 weeks of December, in particular, are the prime time for travel to Hawaii. If you're planning a holiday trip, make your reservations as early as possible, expect crowds, and prepare to pay top dollar for accommodations, car rentals, and airfare.
The off-season, when the best rates are available and the islands are less crowded, is spring (mid-Apr to mid-June) and fall (Sept to mid-Dec) -- a paradox because these are the best seasons to be in Hawaii, in terms of reliably great weather. If you're looking to save money, or if you just want to avoid the crowds, this is the time to visit. Hotel rates and airfares tend to be significantly lower, and good packages are often available.
Note: If you plan to come to Hawaii between the last week in April and early May, be sure you book your accommodations, interisland air reservations, and car rentals in advance. In Japan, the last week of April is called Golden Week because three Japanese holidays take place one after the other. Waikiki is especially busy with Japanese tourists during this time, but the neighboring islands also see dramatic increases.
Due to the large number of families traveling in summer (June-Aug), you won't get the fantastic bargains of spring and fall. However, you'll still do much better on packages, airfare, and accommodations than you will in the winter months.
Because Hawaii lies at the edge of the tropical zone, it technically has only two seasons, both of them warm. There's a dry season that corresponds to summer (Apr-Oct) and a rainy season in winter (Nov-Mar). It rains every day somewhere in the islands any time of the year, but the rainy season sometimes brings enough gray weather to spoil your tanning opportunities. Fortunately, it seldom rains in one spot for more than 3 days straight.
The year-round temperature doesn't vary much. At the beach, the average daytime high in summer is 85°F (29°C), while the average daytime high in winter is 78°F (26°C); nighttime lows are usually about 10°F cooler. But how warm it is on any given day really depends on where you are on the island.
Each island has a leeward side (the side sheltered from the wind) and a windward side (the side that gets the wind's full force). The leeward sides (the west and south) are usually hot and dry, while the windward sides (east and north) are generally cooler and moist. When you want arid, sunbaked, desertlike weather, go leeward. When you want lush, wet, junglelike weather, go windward.
Hawaii is also full of microclimates, thanks to its interior valleys, coastal plains, and mountain peaks. So if the weather doesn't suit you, just go to the other side of the island -- or head into the hills.
On rare occasions, the weather can be disastrous, as when Hurricane Iniki crushed Kauai in September 1992 with 225 mph winds. Tsunamis have swept Hilo and the south shore of Oahu. But those are extreme exceptions. Mostly, one day follows another here in glorious, sunny procession, each quite like the other.
Sun All the Time -- Your best bets for total year-round sun are Waikiki Beach and the Ko Olina (southwest) coast of Oahu.
When Hawaii observes holidays (especially those over a long weekend), travel between the islands increases, interisland airline seats are fully booked, rental cars are at a premium, and hotels and restaurants are busier.
Federal, state, and county government offices are closed on all federal holidays.
State and county offices are also closed on local holidays, including Prince Kuhio Day (Mar 26), honoring the birthday of Hawaii's first delegate to the U.S. Congress; King Kamehameha Day (June 11), a statewide holiday commemorating Kamehameha the Great, who united the islands and ruled from 1795 to 1819; and Admissions Day (third Fri in Aug), which honors the admittance of Hawaii as the 50th state on August 21, 1959.
Other special days celebrated in Hawaii by many people but which involve no closing of federal, state, and county offices are the Chinese New Year (which can fall in Jan or Feb; in 2012, it's Jan 23 and the year of the Dragon; in 2013, it's Feb 10 and the year of the Snake), Girls' Day (Mar 3), Buddha's Birthday (Apr 8), Father Damien's Day (Apr 15), Boys' Day (May 5), Samoan Flag Day (in Aug), Aloha Festivals (Sept-Oct), and Pearl Harbor Day (Dec 7).
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.