Regions of Hawaii

Oʻahu is one million people on one island, and the Koʻolau runs the weather for all of them: the trades stack showers against the windward cliffs while Waikīkī sits dry twenty minutes away, and when the trades quit, the whole island feels it. Winter brings the North Shore swell that made the island the capital of big-wave surfing.

Maui is a valley between two volcanoes, and the valley is a wind tunnel: the trades accelerate between Haleakalā and the West Maui Mountains hard enough to close the harbor while Lahaina sits still and dry in the lee. Upcountry runs twenty degrees cooler than the shore, Hāna takes the rain, and the same downslope wind that dries the leeward side drove the 2023 fire.

The Big Island is the textbook case for why Hawaii has no one forecast: Hilo is one of the wettest cities in America and Kawaihae, ninety minutes around the island, is a desert. Two 14,000-foot-class summits take snow most winters, Kīlauea makes its own weather in Puna, and Kona’s afternoon sea-breeze showers run opposite to every other forecast in the state.

Kauaʻi is the oldest of the islands and the one the rain has had the longest to work on: Waiʻaleʻale is the wettest ground in the country, the canyons it carved flash-flood fast — Hanalei took a national-record 49.69 inches in 24 hours in April 2018 — and Iniki, the strongest hurricane ever to strike Hawaii, crossed the island directly in 1992.