People visiting Hawaii tend to assume that there is either a wet or a dry season. Weather patterns in Hawaii are not that simple and predictable. Weather patterns vary due to trade winds but without a well-defined “rainy season.” For vacation planning purposes, you can’t expect it to be rainy in winter and dry in summer. Summer months do tend to be the driest and sunniest and also the most humid. Winter months usually bring more rain, especially to the windward side of the islands. But usually you don’t have to worry about prolonged rain storms.
One of the most important factors in weather are the trade winds. Prevailing trade winds in Hawaii have a significant affect on air temperatures and, most important, water conditions. Winds come from all directions but mainly from the northeast. From October to the end of April, northeasterly trade winds sometimes are replaced by southwesterly winds known as “Kona Winds.” Winds generally are more persistent during summer months. Trade winds are normally calm in the morning and gradually increase in strength as the day progresses, usually peaking in mid-afternoon. This is one of the main reasons for arranging snorkeling or diving activities in the mornings.
The wettest periods on Oahu are almost always in the wintertime. Tradewinds usually bring varying amounts of rain to Oahu and the other islands from mid-November through late March. Oahu will be really nice during the winter months but just wetter in parts of the island like the East Coast. The island is generally drier on the west side. Waikiki has pleasant weather year-round. Oct. thru Mar. are the months with the most precipitation on Oahu but usually totaling less than 6 days of rain per month.
It makes no sense to plan a Kauai vacation based on which location is sunnier or drier. Waimea probably is the driest spot on the island but Poipu and Lawai offer comparably dry and sunny vacations. Kapaa on the Eastern (Coconut) Coast averages about 50″ of rain annually but the shops, eateries and other attractions available to visitors tend to offset the inconvenience of showers. The wettest area of Kauai, the North Shore, gets much more rain (85”) but has scenery and attractions not to be missed. Thanks to 500 inches of yearly rainfall on Mount Waialeale and 20 inches around Poipu, Kauai earns the reputation of vast extremes in its rainfall.
Weather on Kauai is changeable, not only between places but even within each individual place. Are there seasons on Kauai? Sort of. Call mid-March the beginning of spring when winter storms end. Sunshine days increase and summer kind of begins in May when weather warms somewhat and rains slacken. Trade winds temper the heat and humidity year-round. Trade winds blow about 90% of the time in summer and about 50% in winter. Most important for visitor’s planning a visit to the Garden Isle, remember that spectacular scenery and memorable outdoor adventures occur year round.
Maui’s weather patterns change dramatically depending on where you are on the island. Maui has a large number of microclimates and, within just a few miles, the average rainfall can change by several inches very quickly. Overall it’s fair to say that Maui has great weather. Even in the wettest locations it may be raining one minute and sunny the next. Wet equals lush, so it’s difficult for anyone to argue that wet areas on Maui are less desirable than drier ones.
Maui’s wettest periods almost always occur in winter, between mid-November and late March, when the trade winds bring additional moisture to all the islands. On the South Shore, Kihei, Wailea, and Makena are very dry areas, averaging just a few inches of rain a year. Along the southwest coastline, Lahaina also is fairly dry year-round. The further north you go from Lahaina and Kaanapali towards Kapalua and beyond, the more rain you’ll experience, but only by a very small amount.
Most locations in Upcountry (around Kula) receive 30″-40″ of rain a year, which is a little less than Paia down below on the coast. Eastward from Paia towards Hana, the amount of rain increases considerably, but Hana town itself with 80” annually isn’t all that wet. In case you wondered, over the course of the year, the temperature in Hana is rarely below 61°F or above 88°F. In the wettest months, October to April, the chance of a wet day typically is about 15%, peaking in March. But any time of year is a good time to be in Hana and its marvelous environs.
Big Island Weather
Like all Hawaiian Islands, the Big Island is affected by trade winds that blow NE to ENE. These trade winds bring cool air from the north, often resulting in precipitation along inland-mountain and windward areas. When these winds virtually reverse and become south (Kona) winds, the result can be hot and muggy conditions. Some areas on the Big Island have virtually no rainfall all year-long. Others, like Hilo and Puna, can have rain every day.
The average temperatures near major resort areas on the Kona coast range from 75-85°F in both winter and summer. The Kohala Coast and Waikaloa are almost always sunny year-round. Mauka (meaning inland) and up above the Kohala Coast in Waimea, temperatures of course are much cooler. Further north Hawi and Honokaa on the North Kohala coastline are much wetter at 60″ to 80″ a year. On the east side of the island, the beautiful Hamakua Coast is a wet area. Hilo has earned the title of the wettest large city in the U.S. with as much as 160” of rain annually.