The outstanding features of Hawaii’s climate include mild temperatures throughout the year, moderate humidity, persistence of northeasterly trade winds, significant differences in rainfall within short distances, and infrequent severe storms.
Hawaii is within the tropics which accounts for the relative uniformity through the year in length of day, solar energy and temperature. Hawaii’s longest and shortest days are about 13 1/2 hours and 11 hours, respectively, compared with 14 1/2 and 10 hours for Southern California and 15 1/2 hours and 8 1/2 hours for Maine.
The ocean provides moisture to the air and acts as a giant thermostat. Its temperature varies little compared to areas with large land masses. The seasonal range of ocean surface temperature near Hawaii is only about 6°. Hawaii’s warmest months are not June and July, but August and September. Its coolest months, are not December and January, but February and March, reflecting the seasonal lag in the ocean’s temperature.
Hawaii’s mountains significantly influence every aspect of its weather and climate. The endless variety of peaks, valleys, ridges, and broad slopes, gives Hawaii a climate that is different from the surrounding ocean, as well as a climatic variety within the islands. These climatic differences would not exist if the islands were flat and the same size.
The open sea near Hawaii reaches rainfall averages between 25-30 inches a year. The “orographic,” or mountain-cause rains, forms within the moist trade-wind air as it moves in from the sea and overrides the steep and high terrain of the islands. Another source of rainfall is from cumulus clouds that build over the mountains on calm sunny afternoons. These shows are forceful but brief.
The above product is a condensed chapter on Hawaii’s climate from the Second Edition (University of Hawaii Press, 1983) of the “Atlas of Hawaii.” The author is the late Saul Price, former Hawaii State Climatologist and Staff Meteorologist for the National Weather Service Pacific Region.
Hawaii’s tropical rainforests vary on elevations. Moist to wet forests are commonly found on the windward lowland, montane areas on larger islands and mountain tops of smaller islands. They cover an area of 6,700 km² (2,600 sq mi).
Tropical moist forests of Hawai’i occur as mixed mesic forests (about 750–1,250 m elevation), rain forests (found above mixed mesic forests up to 1,700 m), wet shrublands, and bogs in swampy areas. There are forty-eight different forest types found in the Hawaiian islands.
Due to human presence, lowland and foothill moist forests have been largely eliminated. There is degradation from feral ungulates, development, and recreational activities in montane forests. Introduced weed and tree species, avian malaria, invasive ants, rats, frogs, toads, pigs, goats, and cats all modify native habitats and harm threatened wildlife populations.
The hot, wet weather of the rainforest helps to add water to the atmosphere. It accomplishes this through the many different plants and trees releasing water from their leaves into the air. The moisture from the leaves is then absorbed, or soaked up, into the air. In turn, it can lead to the forming of rain clouds. The clouds then release the moisture in the form of rain. This cycle occurs over and over and over again. This ongoing process helps the rainforests stay healthy and green — which means that the plants can grow, animals can eat and so the ecosystem of the rainforest is in balance.