Hawaii experiences a season often referred to as “winter,” defined by a shift in weather patterns rather than the extreme cold or snowfall found in temperate climates. The islands operate on a two-season climate model: Kau (summer/dry season) and Hoʻoilo (winter/wet season). This seasonal change is subtle, marked primarily by increased precipitation and a minor decrease in temperature. The surrounding ocean acts as a thermal regulator to prevent significant temperature drops, keeping conditions consistently mild throughout the year.
Defining the Wet Season vs. Traditional Winter
Hawaii’s winter season, known as Hoʻoilo, typically spans from November through April, contrasting with the drier summer months that run from May to October. This period is characterized by a higher frequency of storm systems, which bring the majority of the annual rainfall to the islands. The traditional four-season structure of autumn, winter, spring, and summer is not applicable here, as the change is noted almost entirely by moisture levels.
The increased rainfall is often associated with the interruption of the typical northeasterly trade winds by low-pressure systems, which can lead to what are called Kona storms. These weather events introduce winds that blow from the south or southwest, a direction known as kona. Kona storms result in widespread, prolonged rain that can affect even the normally dry, sheltered areas of the islands, making it a time of lush greenery and full waterfalls across the landscape.
Temperature Variations and Regional Differences
The change in temperature during the wet season is noticeable but minor, with the most significant difference occurring between day and night. The average daytime high temperature at sea level during this period is approximately 78°F, about seven degrees cooler than the 85°F high experienced during the summer months. Nighttime temperatures typically drop into the upper 60s Fahrenheit, making light layers occasionally necessary during the evenings.
The true variation in Hawaiian winter weather is geographic, defined by the islands’ massive volcanic terrain and the resulting microclimates. The windward sides, typically the north and east coasts, receive the bulk of the winter rainfall because the prevailing trade winds force moist air upward, causing orographic precipitation. These areas are cooler and cloudier throughout the season. Conversely, the leeward sides are shielded by the mountains and remain significantly drier and sunnier, often experiencing only brief, localized showers. A short drive across an island can take a person from a tropical downpour to clear, warm sunshine.
Unique Seasonal Travel Experiences
The shift in seasonal weather brings about celebrated natural phenomena that draw visitors during the wet season. The dramatic change in ocean conditions is one such event.
Big Wave Surfing
Powerful Pacific storms in the North Pacific generate immense swells that travel thousands of miles. These swells consistently impact the North Shores of islands like Oahu and Maui from November through April, creating the world-renowned big waves that attract professional surfers.
Humpback Whale Migration
The annual migration of North Pacific Humpback Whales is the other major seasonal event. These massive marine mammals arrive in Hawaiian waters to breed and calve, journeying from their summer feeding grounds in Alaska. They seek the warm, shallow, and protected waters surrounding the islands. The official whale season runs from December to April, with the peak viewing period for sightings occurring between late January and early March.