What Climate Zone Is Hawaii In?

With its warm tropical climate, sandy beaches, lush rainforests, and active volcanoes, Hawaii is an incredibly diverse and beautiful place. If you’re wondering exactly what climate zone Hawaii falls into, you’ve come to the right place.

If you’re short on time, here’s a quick answer: Hawaii has a tropical rainforest climate, with warm and wet weather year-round. The islands experience only minor seasonal temperature changes.

Hawaii’s Year-Round Warm and Humid Climate

Consistently High Temperatures

Hawaii is known for its consistently warm and pleasant temperatures all year round. The average daily high temperatures in Hawaii range from 78°F in the “winter” months to 88°F in the “summer” months. With such small fluctuation, Hawaii essentially has endless summer weather with average highs staying above 70°F every month of the year.

The warmer months tend to be July through September, while December through February bring slightly “cooler” temps. However, even the coolest months still see average highs above 78°F, meaning shorts and t-shirts can be worn comfortably year-round in Hawaii’s tropical climate.

Abundant Rainfall

In addition to the consistently warm temps, Hawaii also sees abundant rainfall. The islands have a tropical rainforest climate, meaning heavy rainfall and humidity are the norm. Annual precipitation ranges from 30 to 50 inches on average across the islands.

The windward or northeast sides of the islands tend to be wetter, while the leeward or southwest sides are generally drier. The rainiest months tend to be during Hawaii’s “winter” from October to April when Pacific storms generate heavy rains.

Even in summer the warm tropical air produces brief passing showers on most days. So when packing for a trip to Hawaii, be sure to bring moisture-wicking clothing, rain jackets, umbrellas, and waterproof shoes to comfortably explore the lush Hawaiian landscape in any weather.

Little Seasonal Variation

Unlike the Continental United States with its four distinct seasons, Hawaii experiences very little seasonal variation throughout the year in terms of both temperatures and precipitation. The islands have a tropical climate qualified as Af by the Köppen climate classification system, defined as a tropical rainforest climate with consistent warm temperatures year-round.

Hawaii’s seasons are instead defined more by rainfall, with the “summer” months from May to October being drier while the “winter” months from October to April bring more Pacific storms and rain. However, even during Hawaii’s drier summer periods, passing showers are still a regular occurrence keeping relative humidity consistently high.

The small fluctuations in seasonal averages are minor compared to what most of the mainland experiences. Simply put, Hawaii maintains hot, humid, and green conditions 12 months a year!

Hawaii’s Climate Classification Systems

Köppen Climate Classification

The Köppen climate classification system, first developed in 1884 by Wladimir Köppen, categorizes Hawaii’s climate as tropical wet and dry or savanna (Aw). This means Hawaii has a tropical climate with a distinct wet season during winter months and a dry season during summer months.

Average temperatures are above 18°C (64°F) year-round.

Trewartha Climate Classification

The Trewartha climate classification modifies the Köppen system and places Hawaii firmly in the tropical wet climate zone. This subsystem focuses on subtleties in tropical climates. Hawaii fits into the tropical wet climate category where mean monthly temperatures are above 18°C (64°F) in every month of the year and annual precipitation totals are greater than 1500mm (59 inches).

National Geographic Ecosystems

National Geographic divides Hawaii’s climate into tropical moist forests and tropical grasslands, savannas, and shrublands zones. The tropical moist forests occur on windward mountain slopes that receive plentiful rainfall.

The drier leeward mountain slopes and coastal regions fall into the tropical grasslands and shrublands designation.

Regional Climate Differences Across the Islands

Windward vs. Leeward Sides

Hawaii’s islands have very different climates on their windward (east-facing) and leeward (west-facing) sides. The windward sides face into the prevailing northeasterly trade winds and receive much more rainfall.

For example, Mount Waialeale on Kauai’s rainy windward side receives over 460 inches of rain per year, making it one of the wettest places on Earth!

In contrast, the leeward sides are in the rain shadow and have a much drier climate. For instance, Puako on the leeward Kohala Coast of the Big Island gets less than 10 inches of rain per year. The leeward sides also tend to be warmer as the descending air warms adiabatically.

Altitude Effects

There are also major climate differences across altitudes on the Hawaiian Islands. In general, temperatures decrease by about 3°F for every 1,000 feet gained in elevation. So the high peaks like Mauna Kea can have winter snow, while coastal areas remain quite warm and sunny year-round.

For example, Hilo on Hawaii Island has an average high of 81°F being right on the windward coast, while the Onizuka Center on Mauna Kea at 9,200 feet has an average high of just 50°F despite only being 30 miles away horizontally.

Urban Heat Island Effect

Within urban areas like Honolulu on Oahu, there is also a phenomenon called the urban heat island effect. All the paved surfaces and buildings absorb and radiate heat, causing urban centers to be up to 10°F warmer than outlying areas, especially at night.

According to a recent University of Hawaii study, the Honolulu urban heat island has contributed to a doubling of the number of heat waves in the last few decades. This highlights the localized effects development can have on microclimates within the islands.

Threats to Hawaii’s Climate

Invasive Species

Invasive species pose a huge threat to Hawaii’s native ecosystems and climate resilience. As an isolated island chain, Hawaii’s native species evolved in the absence of predators or competitors. Invasive species can out-compete native species for resources or predate on them (Hawai’i Invasive Species Council).

For example, feral pigs disturb forest soils and spread invasive plants, and mongoose and rats prey on native bird species critical for plant pollination and seed dispersal. Introduced mosquitoes have brought devastating diseases that threaten native bird populations as well.

Removing invasive species and preventing new introductions would greatly aid Hawaii in adapting to climate change.

Sea Level Rise

As global temperatures rise due to climate change, sea levels are rising as well. Scientists project that sea levels may rise by 3.2 feet by 2100 (Hawaiʻi Sea Level Rise Viewer). This poses a huge threat to Hawaii’s low-lying coastal areas. Popular beaches may be submerged or see severe erosion.

Sea level rise causes saltwater to intrude into groundwater, threatening freshwater sources (which are already limited on the islands). It also leads to dangerous coastal flooding and storm surge during extreme weather events.

Mitigating climate change globally is key to curbing sea level rise, but Hawaii will still need significant local adaptation measures such as moving coastal infrastructure and homes inland.

Changing Rainfall Patterns

Scientists project Hawaii’s rainfall patterns will change as the climate warms. Wet areas may get wetter, receiving heavier downpours, while dry leeward areas get drier (Civil Beat). Rainfall is already becoming more variable, leading to periods of drought punctuated by extreme precipitation.

These shifting precipitation patterns stress native ecosystems adapted to moderate rainfall. Wetter weather favours invasive species, while drought stresses and kills native plants and animals. Changing rainfall also threatens Hawaii’s agriculture and food security.

Mitigating climate change globally can help limit shifts in Hawaii’s sensitive rainfall patterns. Locally, improving water storage and distribution infrastructure could aid adaptation.

Conclusion

To summarize, Hawaii falls into the tropical rainforest climate zone, experiencing warm and wet weather all year long with little seasonal variation. While the islands share an overall tropical climate, there are some notable regional differences determined by topography and location.

Moving forward, threats like invasive species, rising sea levels, and changing rain patterns may alter Hawaii’s climate in the years to come.

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