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Air & water temperature, rainfall and mountain conditions
The Hawaiian Islands have a moderate tropical climate with gentle northeasterly tradewinds and warm Pacific waters almost year-round. Temperatures vary little from place to place, except at higher elevations (see "mountain conditions," below). The average annual temperature of 75 degrees Fahrenheit (23.9 degrees Celsius) fluctuates only a few degrees from summer (May through October) to winter (November through April). The recorded temperature in the state has ranged from 12 degrees F (-11.1 degrees C) near the summit of Mauna Kea in 1979 to 100 degrees F (37.8 degrees C) at Pahala (on the Big Island of Hawaii) in 1931.

Rainfall
Unlike the temperature, Hawaii's rainfall varies tremendously according to location. The highest amount of rainfall is usually at moderate elevations on the windward (east) sides of the islands and is due to moisture-laden oceanic tradewinds. Leeward (western) locations are drier, because they are shielded from the damp winds by mountains. The lowest rainfall in the state is at Puako in leeward Hawaii (Big Island), which averages 5.7 inches (145 mm) of rain per year. Mt. Wai'ale'ale on Kaua'i is considered the "world's wettest spot," averaging 486 inches (12,344 mm) of rainfall per year.

Mild rain and wind storms are more frequent during Hawaii's winter months (November through April), but they generally clear within 24 hours. Although severe storms are uncommon (such as hurricanes, or downgraded hurricanes called "tropical storms"), they do make landfall in the Central Pacific, on average, every eight to 10 years. The state's last hurricane, Hurricane Iniki, was in September 1992, causing an estimated $1 billion in damage. Most of the destruction was on the island of Kaua'i. The state's annual "hurricane season" — when these storms are most likely to form in the Pacific — is June through September.

Water Temperature
Hawaiian waters are inviting year-round, averaging 74 degrees F (23 C) and reaching close to 80 degrees F (26 C) in the summer months. Surf conditions vary year-round according to seasonal storms in the Pacific.

Mountain conditions
Hawaii has mountainous regions. At higher elevations (such as Mauna Kea on the Big Island, Haleakala on Maui or Koke'e on Kaua'i) the temperature drops an average of 3.5 degrees F for every 1,000 feet of elevation above sea level. This means that when it's 80 degrees F on the beach it may be only 50 degrees F at the 10,023-foot-high summit of Haleakala.

During the winter months (November through April), it's likely that the Big Island's Mauna Kea and Maui's Haleakala will have moderate to heavy snowfall. While there is no formal ski area in Hawaii, residents do occasionally sled and ski on Mauna Kea's slopes.

Winter temperatures on Mauna Kea range from 25 to 40 degrees F (-4 to 4 C), but wind chill can bring the temperature to below zero at the summit.

Average Temperature, Rainfall, Humidity
Average January temperature range:
Honolulu: 65 to 79 degrees F (18.3 to 26.1 C)
Hilo: 63 to 80 degrees F (17.2 to 26.7 C)

Average July temperature range:
Honolulu: 73 to 87 degrees F (22.8 to 30.6 C)
Hilo: 68 to 83 degrees F (20 to 28.3 C)

Average annual temperature:
Honolulu: 77 degrees F (25 C)
Hilo: 73 degrees F (22.8 C)

Average annual precipitation:
Honolulu: 23 inches (584 mm)
Hilo: 134 inches (3404 mm)

Average annual snowfall:
Honolulu: 0
Hilo: 0

Average number of days per year with appreciable precipitation:
Honolulu: 102
Hilo: 282

Average daily relative humidity:
Honolulu: 63%
Hilo: 75%

Average number of clear days per year:
Honolulu: 90
Hilo: 30 Storm tracking

During Hawaii's storm season (June through September) an average of four or five tropical cyclones (hurricanes) are generated in the Central Pacific, but few come close to the Islands and only three have made landfall in the past 50 years. Much of the hurricane season in the Islands is spent enduring remnants of weakened storms, called Tropical Storms.