Hawaii Climate

The American state of Hawaii, which covers the Hawai'ian Islands, is tropical but it experiences many different climates, depending on altitude and weather. The islands receive most rainfall from the trade winds on their north and east flanks (the windward side) as a result of orographic precipitation. Coastal areas, in general, and especially the south and west side or leeward sides, tend to be drier.

In general, the Hawaiian Islands receive most of their precipitation during the winter months (October to April). Drier conditions generally prevail from May to September, but the warmer temperatures increase the risk of tropical cyclones.

Average temperature and rainfall of Hawaii

Annual temperature and rainfall of Hawaii

Temperature

One distinctive feature of Hawaii’s climate is the small annual variation in temperature range. This is because there is only a slight variation in length of night and day from one part of Hawaii to another and because all its islands lie within a narrow latitude band. The small variations in the length of the daylight period, together with the smaller annual variations in the altitude of the sun above the horizon, result in relatively small variations in the amount of incoming solar energy from one time of the year to another. The surface waters of the open ocean around Hawaii range from 77 °F (25 °C) between late February and early April, to a maximum of 83 °F (28 °C) in late September or early October. With water temperatures this mild for hundreds of miles around, the air that reaches Hawaii is neither very hot nor very cold.

The other reason for the small variation in air temperature is the nearly constant flow of fresh ocean air across the islands. Just as the temperature of the ocean surface varies comparatively little from season to season, so also does the temperature of air that has moved great distances across the ocean; the air brings with it to the land the mild temperature regime characteristic of the surrounding ocean. In the central North Pacific, the trade winds represent the outflow of air from the great region of high pressure, the North Pacific High, typically located well north and east of the Hawaiian Islands.

The Pacific High, and with it the trade-wind zone, moves north and south with changing angle of the sun, so that it reaches its northernmost position in the summer. This brings trade winds during the period of May through September, when they are prevalent 80 to 95 percent of the time. From October through April, the heart of the trade winds moves south of Hawaii; however, the winds still blow much of the time. They provide a system of natural year-long ventilation throughout the islands and bring mild temperatures characteristic of air that has moved great distances across tropical waters.

Wind

Island wind patterns are very complex. Though the trade winds are fairly constant, their relatively uniform air flow is distorted and disrupted by mountains, hills, and valleys. Usually winds blow upslope by day and downslope by night. Local conditions that produce occasional violent winds are not well understood. These are very localized, sometimes reaching speeds of 60 to 100 mph (100 to 160 km/h) and are best known in the settled areas of Kula and Lahaina on Maui. The Kula winds are strong downslope winds on the lower slopes of the west side of Haleakala. These winds tend to be strongest from 2,000 to 4,000 ft (600 to 1,200 m) above mean sea level.

The Lahaina winds are also downslope winds, but are somewhat different. They are also called "lehua winds" after the ʻōhiʻa lehua (Metrosideros polymorpha), whose red blossoms fill the air when these strong winds blow. They issue from canyons at the base of the western Maui mountains, where steeper canyon slopes meet the more gentle piedmont slope below. These winds only occur every 8 to 12 years. They are extremely violent, with wind speeds of 80–100 mph (130–160 km/h) or more.

True-color Satellite View of Hawaii

Wind Speed & Direction of Hawaii

A true-color satellite view of Hawaii shows that most of the flora on the islands grow on the north-east sides, which face the trade winds. The texture change around the calmer south-west of the islands is the result of the shelter provided from the islands.

The right image above shows the winds around the Hawaiian Islands measured by the Seawinds instrument aboard QuikSCAT during August 1999. Trade winds blow from right to left in the image. The bottom image shows the ocean current formed by the islands’ wake. Arrows indicate current direction and speed, while white contours show ocean temperatures. The warm water of the current generates winds that sustain the current for thousands of miles.

Instant Weather Obeservation in Energy Lab, Hawaii Preparatory Academy