Home : About Oahu : Geography & Climate

Oahu, an island occupying 597 square miles, is the second oldest island in the Hawaiian chain of visitable islands. She lies between her sister islands Kauai and Maui. Geographically, Oahu is made up of two major mountain ranges that were once two shield volcanoes which have long since become extinct. These two mountain ranges – the Waianae range in the west and Koolau range in the east – run almost parallel to each other. The Waianae range is the oldest part of Oahu at about four million years old. Over a hundred ridges extend from the spines of each range. As a result, there are valleys, bays and amazing scenery.

There are several smaller post-shield volcanic outcroppings scattered throughout the island, all of which are extinct. These appear in the form of volcanic cones and heads usually no greater than 1,000 feet high and a mile in diameter. The most famous of these former craters include Diamond Head and Punchbowl craters, both popular visitor attractions. Koko Head crater is the youngest part of Oahu at about 32,000 years old.

The Koolau mountain range spans the length of the island’s eastern coast for about 34 miles from the vicinity of Kahuku in the North to Makapuu in the South. The Koolau range separates the Windward coast of Oahu from the central plains of Oahu (Central Oahu). On the Windward (east) side, many hundred thousand years of constant gales have carved beautiful rippling rock faces, near-vertical ridges and precipitous cliffs. Today, the Windward coast tends to be Oahu’s wetter and greener side of the island.

The Waianae mountain range lies on the west side of the island, separating Central Oahu from the Leeward coast. For the most part, it remains considerably warmer and drier. The Waianae crest’s personality is higher, narrow, exposed, boulder-ish in places, and sharp, its flora sparser and drier than its Koolau mate. Where the Waianae valleys and gulches lack in lush, bounding verdure, it makes up for with gorgeous red and earthen carvings and peaks.

Climate

Average air temperature ranges from 74 degrees F (23 degrees C) to 88 degrees F (31 degrees C) with moderate humidity of 53% during the day. Even the warmest months are comfortable with blowing trade winds.