Save money on your next flight
Skyscanner is the world’s leading flight search engine, helping you find the cheapest flights to destinations all over the world.
With its lush greenery, vibrant rainbows, and cascading waterfalls, the Hawaiian Islands are defined by their relationship with rainfall.
If you’re short on time, here’s a quick answer to your question: Hawaii gets an average of 75 inches of rain per year, with significant variability across the islands and based on elevation and terrain.
In this comprehensive guide, we’ll explore Hawaii’s diverse precipitation patterns, seasonal changes, differences based on location, history, impacts, and future predictions for the state’s iconic rainfall.
Background on Hawaii’s Unique Climate
Pacific Ocean Influences
Hawaii’s climate is greatly influenced by the vast Pacific Ocean that surrounds the islands. The ocean helps moderate temperatures year-round, keeping conditions relatively warm and humid. The average high temperatures at sea level range from 85°F in the summer to 79°F in the winter.
The Pacific also brings consistent trade winds that blow from the northeast.
Trade Winds
The cooling trade winds blow 80% of the time, especially on the windward sides of the islands. These consistent breezes moderate the heat and bring orographic rainfall as moisture-laden air is pushed up mountain slopes.
The trade winds bring Hawaii sunny skies and passing showers on the windward sides contrasted by clear, drier conditions on the leeward sides.
Hawaiian Hot Spot
The Hawaiian islands sit over a hot spot deep in the Earth’s mantle, which brings geothermal heat from below. This volcanic origin helps elevate subterranean temperatures, warming groundwater and streams throughout the islands.
Elevated geothermal energy manifests at Hawaii Volcanoes National Park, where lava flows into the ocean and steam vents hiss from cracks in the Earth’s surface.
Elevation Effects
Hawaii’s elevation extremes create strikingly different localized climates. High mountain peaks like Mauna Kea can have snowy conditions in winter. Yet just 45 miles away near sea level, Kona sees consistent warmth year-round perfect for growing coffee and tropical fruits.
The tall mountains wring moisture from trade wind clouds, yielding extreme rainforest conditions on windward slopes.
Annual and Monthly Rainfall Patterns
Rainiest Locations
The windward sides of the Hawaiian islands receive much more rain than the leeward, drier sides. For example, Mount Waiʻaleʻale on Kauai has an incredible average yearly rainfall of 460 inches! Meanwhile, the Kohala district of the Big Island only gets about 20 inches annually.
Why such a difference? The mountains on the windward sides force warm, moist air coming off the ocean to rise rapidly. As this air cools at higher altitudes, clouds and rain form. Hence the super high rainfall totals in these areas, especially at higher elevations.
Seasonal Impacts
Hawaii has two distinct seasons – a warmer summer from May to October, when trade winds blow out of the northeast; and a cooler winter November to April, when storms from the west and southwest are more common.
Winter is Hawaii’s rainy “wet” season, especially on north and west facing shores. Maui’s West Maui Mountains get doused with nearly 200 inches during these months! But even during Hawaii’s drier summer, mountain peaks and windward areas still see consistent rains produced by trade wind weather patterns.
El Niño Effects
During an El Niño year, Hawaii’s typical rain and weather patterns get disrupted. Trade winds weaken, storms track further south, and rain tends to concentrate on the southern sides of the islands instead of the usual windward areas.
For example, rainfall totals on Maui’s normally dry leeward sides and plains sometimes end up comparable to the normally drenched windward north shore and slopes of Haleakalā during strong El Niño periods.
1991 and 1997 saw over 150 inches fall at the airports in Kahului and Kihei on central and south Maui.
Historical Trends and Predictions
Long-term Patterns
Hawaii’s rainy seasons tend to follow consistent long-term patterns. The islands typically see more rain on their north and east facing shores, as moist trade winds blow in from the northeast. The wettest areas are on the windward sides of the islands.
For example, Mount Waiʻaleʻale on Kauai receives over 460 inches of rain per year on average, making it one of the rainiest spots on Earth!
There are also microclimates on each island based on topography. Volcanic peaks ring the islands and wring moisture out of passing clouds and storms, leading to wetter conditions at higher elevations. The peaks can see brief but intense rainstorms.
Climate Change Impacts
Climate change is already impacting rainfall patterns in Hawaii. Since the 1950s, rainy seasons have become more irregular. Both extremely heavy rainstorms and longer droughts have increased in frequency.
One study found a 45% increase in heavy rainfall events in Honolulu since the 1950s. Droughts may threaten water supplies, agriculture, ecosystems and increase wildfire risks in drier areas.
Rising sea levels also increase coastal flooding risks during high tides or storms. Overall Hawaii sees 3-30% less annual rainfall now compared to early 20th century averages. Climate change brings uncertainty to long-established patterns.
Future Projections
Climate models project diverging futures for Hawaii’s rainy regions. Windward areas may see 5-30% increases in rainfall by end of century. Leeward sides are expected to become 5-60% drier on average.
| Island | Rainier Regions | Drier Regions |
|---|---|---|
| Kauai | North shore | Southwest |
| Oahu | Koolau Range | Leeward coast |
| Maui | Northeast | Southwest |
| Hawaii | Windward coast | Kona coast |
While future projections carry uncertainty, it is clear Hawaii’s rainfall is already becoming more variable under climate change. Understanding these shifts can help communities better prepare.
Conclusion
With an intricate relationship between terrain, elevation, seasonal shifts, and even global climate systems, precipitation across Hawaii reveals itself to be incredibly complex.
Despite regional and seasonal variability, most of the islands experience between 40 to 200 inches of rainfall per year, allowing for the lush landscapes Hawaii is renowned for worldwide.
As climate change continues altering global weather patterns in the 21st century and beyond, tracking Hawaii’s iconic rain levels will reveal even deeper connections between the isolated volcanic peaks and our planet’s delicate atmospheric balance.
