Climate of Hawaii

Climate Of Hawaii

The U.S. 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 flanks 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 hurricanes.

Temperatures at sea level generally range from highs of 85–90 °F (29–32 °C) during the summer months to 79–83 °F (26–28 °C) during the winter months. Rarely does the temperature rise above 90 °F (32 °C) or drop below 65 °F (18 °C) at lower elevations. Temperatures are lower at higher altitudes; in fact, the three highest mountains of Mauna Kea, Mauna Loa, and Haleakala often receive snowfall during the winter.

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 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.

Temperatures of 90 °F (32 °C) and above are quite uncommon (with the exception of dry, leeward areas). In the leeward areas, temperatures may reach into the low 90’s several days during the year, but temperatures higher than these are unusual. The highest temperature ever recorded on the islands was 100 °F on April 27, 1931 in Pahala.

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.