Kauai ranks among the wettest places in the world. Indeed, its central summit area of Waialeale is often regarded as the wettest spot on Earth. But, as everywhere on the main or “high” Hawaiian Islands, the Garden Isle’s rainfall is not evenly distributed, both geographically and seasonally.
Kauai’s rainy season happens to be when most tourists come to the island. In this article, we’ll run through the basics of Kauai’s precipitation patterns, what the weather’s like during the rainy season, and how it might impact your travel here.
Kauai and the rest of the Hawaiian Islands experience two main seasons. Summer—the “dry season,” so to speak—runs from about May to October. Winter—the “rainy season”—prevails from November to April. These periods correspond to traditional Hawaiian seasons: Kau in summer, Hoo-ilo in winter.
This two-season setup reflects Kauai’s position at the northern edge of Earth’s tropical zone. As on mainland North America, summer is the “high-Sun” season, winter the “low-Sun season.” But given Kauai’s location in the tropics, this difference in the relative position of the Sun in the sky doesn’t result in drastic variation in the island’s predominantly warm temperatures (the 70s and 80s F) year-round.
The main seasonal differences have to do with the location and strength of a persistent high-pressure system, the Pacific High, usually located northeast of the Hawaiian Islands. Air circulation around the Pacific High provides the northeasterly trade winds that dominate Hawaiian weather. The Pacific High is farther north and stronger in summer, which makes this the season of the steadiest trade winds. In winter, the high-pressure system shifts southward with the sun and weakens. Thus, this season is when the northeasterly trades, while still the norm, are more often interrupted by different airflow patterns.
The heaviest tourism in Kauai overlaps with the winter rainy season, with the busiest visitation months generally being December to April. That’s not a huge surprise. After all, a Hawaiian “winter” is definitely a friendlier season than its counterpart on most of the North American mainland.
Rainfall Patterns on Kauai
Before digging into the nuts-and-bolts of the rainy season on Kauai, it’s worth sketching out the basic overall rainfall patterns on the island. Essentially, this is the distribution of rainfall under the typical trade-wind weather that prevails on Kauai more than three-quarters of the year. It is the combination of Kauai’s position within the Northeast Trade Wind Belt and its terrain that establishes where and how much rain falls on the island.
It’s the same general story throughout the main Hawaiian Islands, which exhibit some of the most extreme geographic variations in rainfall anywhere on the planet. The northeasterly trades are warm and moist, but in the absence of high-standing terrain, they aren’t compelled to drop that moisture. The average annual rainfall over the open Pacific surrounding Hawaii is about 20 or 25 inches.
But more than 70 inches of rain falls yearly on the islands, averaged out across their land area. And up on the summit of Mount Waialeale, more than 5,200 feet high, the elevated interior of Kauai receives about 430 inches of average rainfall per year. That’s the highest average rainfall recorded anywhere on Earth, though Maui’s Big Bog may compare.
The reason for this high rainfall is that the northeasterly trade winds are forced to rise by Kauai’s mountainous profile. This forced ascent causes the air to cool and because colder air can hold less moisture, clouds condense and precipitation falls.
So the windward side and high interior of Kauai are quite wet. Despite summer and winter commonly being differentiated as the dry vs. wet seasons, windward rainfall at middle to high elevations on Kauai is common throughout the year. Average rainfall increases rapidly up the northern and northeastern slopes of the island, which receive about 70 to 200 inches a year. And, again, the interior Waialeale heights are getting anywhere from 300 to 400-plus inches.
But because the journey up and over Mount Waialeale wrings out the trade winds, the leeward flank of Kauai is much drier. Much of it gets less than 40 inches of rainfall per year. Less than 20 inches fall on the coastal strip of the far west and southwest.
So this basic trade-wind pattern shakes out to the windward side of Kauai being cloudier and wetter, and the leeward side sunnier and drier.
Kauai’s Winter/Rainy Season
Defining anywhere from 80 to 95 percent of summer, typical trade-wind weather is still commonplace during winter on Kauai. But it may be interrupted for days or even weeks by non-trade weather systems. These include the low-pressure disturbances known as Kona storms. Kona means “leeward,” and refers to the fact that these storms often cause westerly or southerly winds in Hawaii as opposed to the normal northeasterly trades.
Kona storms as well as passing cold fronts and upper-level lows—all most frequent in winter with breakdowns in the trades—are responsible for most of Kauai’s major storms. (Certain storms occur under trade-wind flow, it’s worth noting. And hurricanes and tropical storms, though rare overall in the Hawaiian Islands, do sometimes affect Kauai. A case in point was Hurricane Iniki, which made a direct hit on Kauai in September 1992. It damaged or destroyed thousands of homes and interrupted filming of Steven Spielberg’s blockbuster Jurassic Park.)
Kauai as a whole does get more rainfall in the winter months than the summer: The wettest months, usually November and December, get an average of 4.7 or more inches of rain, while both June and August average under two inches. The term “rainy season,” though, is a little misleading, given that the windward side often sees clouds and rain showers throughout the year. Winter might be better thought of as the “stormy season.” (That’s a bit misleading too, though: While most Kauai winters see several major storms, some years bring none at all.)
Major winter storms tend to produce the most intense rainfall. On January 24 and 25, 1956, Kauai got walloped by an extremely wet storm that dropped a minimum of a foot of rain in one hour.
Because these winter storms are often coming from westerly or southerly directions, or are stronger and more organized than trade-wind showers, they can bring a lot of rain to Kauai’s “dry side.” Leeward locations may get much of their yearly rainfall total in these deluges.
Dealing With Kauai’s Rainy Season
Rain only rarely really spoils sightseeing and other tourism on Kauai, even during the rainy season. Typical trade-wind showers are typically light and brief. They also often occur at night. And if you’re tired of prevailing cloudiness on the windward side, you don’t need to drive very far to get to the sunny leeward side of the island, where locations such as Waimea Canyon or Poipu are usually bright and dry.
A Kona storm or other winter storm may bring torrential rainfall to anyplace on the island. Usually, though, they’re not very long-lasting. You may experience a few days of rainy weather, but on an extended vacation, you’re likely to see plenty of sunshine during the winter.
A few considerations for wet periods during Kauai’s rainy season:
- A lot of rain means Kauai’s abundant waterfalls going at full force—and many ephemeral falls suddenly streaking mountainsides and ridgeslopes in spectacular fashion. So a Kauai rainstorm is awesome for waterfall sightseeing and photography.
- Heavy or extended rainfall can make Kauai trails and backroads treacherous. Many are best avoided until conditions dry out.
- While Kauai’s spectacular scenery, hiking trails, and beaches are big-time draws, there’s lots you can explore indoors when it’s wet outside. Check out our roundup of the island’s best rainy-day destinations and activities!