The island of Hawai’i is a place of tremendous climate diversity. From tropical to sub-arctic, the Big Island has it all.
Hawai’i has eleven of the thirteen climatic zones defined in the Koppen Climate Classification System. Developed by Wladimir Koppen in 1884, this climate system is based on average values of temperature and precipitation as well as the distribution of native vegetation. Hawai’i only lacks the extremes of cold winters and summer heat waves.
The primary reason for this wide range of climates is topography. Two huge volcanic mountains, Mauna Kea (13,796 feet) and Mauna Loa (13,679 feet), dominate the landscape of Hawai’i. Since air temperature decreases 3.6°F per one thousand feet, it can be in the 80’s at the beach and below freezing in the summit regions on any given day. Mauna Kea, the White Mountain, even supports a seasonal snow-pack.
These mountains also create orographic rainfall and affect the overall distribution of precipitation on the island. When warm, moist air is forced up along the windward slopes, it condenses into clouds that produce rain. This precipitation supports the island’s lush rainforests and cascading waterfalls. The leeward side of the mountains, where the air descends, is sunnier and more arid.
The vast assortment of climate zones on Hawai’i is remarkable for an island roughly the size of Connecticut. In many ways, Hawai’i is an island of all seasons.
San Francisco, a city known for its fog, is actually a composite of microclimates. Last week, I was visiting the Bay Area and was reminded of its unique climate situation.
The area, in general, has a Mediterranean climate with mild, wet winters and dry summers. It is rare for the city to get warmer than 70°F in summer or cooler than 45°F in winter. Situated on a peninsula along the California coastline, San Francisco is kept mild by the Pacific Ocean’s chilly currents and local coastal upwelling.
Famous for its hills, the city’s complex topography is another major influence on its climate. The Golden Gate, a break in the mountainous Coast Range, funnels Pacific air into the Bay Area. The hills and basins of the peninsula then capture and divert the circulating marine air in intricate ways, forming a variety of microclimates. As a result, weather conditions can vary widely across short distances, such as 10°F between neighborhoods. In San Francisco, the forty hills that form the center of the city create a general weather divide. The western side of the city usually bears the brunt of the incoming Pacific air, with cool temperatures, strong winds, and fog. The more sheltered eastern side generally sees more sun and warmer temperatures.
On a larger regional scale, temperature differences have an even wider scope. For example, the average high temperature in July in the city is 68°F, while temperatures can reach 100°F in the Sacramento Valley, just 50 miles inland.