The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles (2,400 km) from the island of Hawaiʻi in the south to northernmost Kure Atoll (the northwesternmost island in Hawaii is Green Island, which is joined to the Kure Atoll). Excluding Midway, which is an unincorporated territory of the United States, the Hawaiian Islands form the U.S. state of Hawaii. Once known as the "Sandwich Islands", the archipelago now takes its name from the largest island in the group.
The islands are the exposed peaks of a great undersea mountain range known as the Hawaiian-Emperor seamount chain, formed by volcanic activity over a hotspot in the Earth's mantle. At about 1,860 miles (3,000 km) from the nearest continent, the Hawaiian Island archipelago is the most isolated grouping of islands on earth.
(via Wikipedia)
Captain James Cook visited the islands on January 18, 1778 and named them the "Sandwich Islands" in honor of John Montagu, 4th Earl of Sandwich, who was one of his sponsors as the First Lord of the Admiralty.
The chain of islands or archipelago formed as the Pacific plate moved slowly northwestward over a hotspot in the Earth's mantle at about 32 miles (51 km) per million years. Hence the islands in the northwest of the archipelago are older and typically smaller, due to longer exposure to erosion. The only active volcanism in the last 200 years has been on the southeastern island, Hawaiʻi, and on the submerged but growing volcano at the extreme southeast, Loʻihi. The Hawaiian Volcano Observatory of the U. S. Geological Survey documents recent volcanic activity and provides images and interpretations of the volcanism.
The Hawaiian Islands are subject to tsunamis, great waves that strike the shore. Tsunamis are most often caused by earthquakes somewhere in the Pacific. The waves produced by the earthquakes travel at speeds of 400–500 miles per hour and can affect coastal regions thousands of miles away.
The Hawaiian Islands are home to a large number of endemic species. The plant and animal life of the Hawaiian Islands developed in nearly complete isolation over about 70 million years. Mammals were absent until they arrived with the first human settlers.
Hawaii (state) 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.
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 (97 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 (610 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 to 100 mph (160 km/h) or more.
Under trade wind conditions, there is very often a pronounced moisture discontinuity between 4,000 and 8,000 feet (1,200–2425 m). Below these heights, the air is moist; above, it is dry. The break (a large-scale feature of the Pacific High) is caused by a temperature inversion embedded in the moving trade wind air. The inversion tends to suppress the vertical movement of air and so restricts cloud development to the zone just below the inversion. The inversion is present 50 to 70 percent of the time; its height fluctuates from day to day, but it is usually between 5,000 and 7,000 feet (1,500–2,100 m). On trade wind days when the inversion is well defined, the clouds develop below these heights with only an occasional cloud top breaking through the inversion. These towering clouds form along the mountains where the incoming trade wind air converges as it moves up a valley and is forced up and over the mountains to heights of several thousand feet. On days without an inversion, the sky is almost cloudless (completely cloudless skies are extremely rare). In leeward areas well screened from the trade winds (such as the west coast of Maui), skies are clear 30 to 60 percent of the time. Windward areas tend to be cloudier during he summer, when the trade winds and associated clouds are more prevalent, while leeward areas, which are less affected by cloudy conditions associated with trade wind cloudiness, tend to be cloudier during the winter, when storm fronts pass through more frequently. On Maui, the cloudiest zones are at and just below the summits of the mountains, and at elevations of 2,000 to 4,000 ft (610 to 1,200 m) on the windward sides of Haleakala. In these locations the sky is cloudy more than 70 percent of the time. The usual clarity of the air in the high mountains is associated with the low moisture content of the air.
Frequent light showers fall in Hawaii. On windward coasts, many brief showers are common, not one of which is heavy enough to produce more than 0.01 in (0.25 mm) of rain. The usual run of trade wind weather yields many light showers in the lowlands, whereas torrential rains are associated with a sudden surge in the trade winds or with a major storm. Hana has had as much as 28 in (710 mm) of rain in a single 24-hour period.
The hurricane season in the Hawaiian Islands is roughly from June through November, when hurricanes and tropical storms are most probable in the North Pacific. These storms tend to originate off the coast of Mexico (particularly the Baja California peninsula) and track west or northwest towards the islands.
Despite being a tiny speck within the vast Pacific Ocean, the Hawaiian Islands have a surprising effect on ocean currents and circulation patterns over much of the Pacific. In the Northern Hemisphere, trade winds blow from northeast to southwest, from North and South America toward Asia, between the equator and 30 degrees north latitude. Typically, the trade winds continue across the Pacific — unless something gets in their way, like an island.
