Hawaii does have seasons, but they differ significantly from the four distinct periods found in temperate zones. The climate is defined by remarkable temperature stability throughout the year. The seasonal changes are subtle, marked primarily by shifts in precipitation patterns and the consistency of the trade winds. While the differences may not be dramatic, they are noticeable enough to be categorized into two main periods.
Defining the Two Primary Seasons
The Hawaiian year is divided into two primary seasons: a warmer, drier summer known as Kaua, and a cooler, wetter winter called Hoʻoilo. The Kaua season generally spans from May through October and is characterized by the most reliable presence of the northeast trade winds. These steady winds help to regulate the heat, even as average daytime temperatures at sea level reach approximately 85 degrees Fahrenheit.
The Hoʻoilo season runs from November to April and is the period when the islands receive the majority of their rainfall. During this time, the trade winds become weaker and less consistent, leading to more variable weather. The average daytime high temperature drops slightly to about 78 degrees Fahrenheit, creating a difference of roughly seven degrees between the two seasons.
A feature of the winter season is the occasional occurrence of Kona low systems. These are low-pressure systems that disrupt the typical weather patterns. Kona lows bring widespread, heavy rain and strong winds that blow from the south or southwest, a direction that affects the usually dry leeward sides of the islands. The resulting heavy rainfall can sometimes lead to localized flooding.
The Influence of Microclimates
The most significant variation in Hawaiian weather is not seasonal but geographical, driven by microclimates. The interaction between the prevailing northeast trade winds and the islands’ mountainous terrain creates contrasts in weather over short distances. This effect is known as orographic precipitation, where moisture-laden air is forced upward, cools, and releases rain.
The windward (northeast) sides of the islands are perpetually wet and lush, as they constantly intercept the trade winds and the resulting rainfall. Conversely, the leeward (southwest) sides are shielded by the mountains, creating arid, sunny conditions that are drier year-round. This geographical variation often overrides the subtle differences between Kaua and Hoʻoilo, meaning a dry leeward coast in winter may be sunnier than a windward coast in summer.
Altitude also plays a role in creating these varied environments. Temperatures decrease by approximately 3.5 degrees Fahrenheit for every 1,000 feet of elevation gain. The summits of the highest volcanoes experience sub-freezing temperatures. These peaks regularly receive snow during the Hoʻoilo period.
Practical Effects on Ocean and Daylight
The seasonal climate shifts affect the ocean and the amount of daylight. During the Hoʻoilo period, winter storms track across the North Pacific, generating large swells. These swells travel thousands of miles to impact the north-facing shores of the islands, creating the legendary big waves.
The Kaua season sees the North Pacific storms subside, leading to calmer waters on all coastlines. Ocean temperatures remain comfortable year-round, but the sea surface temperature peaks in late summer and early fall, reaching highs around 80 degrees Fahrenheit. This difference in wave action is the most noticeable seasonal change.
The change in the solar cycle is also an effect. The difference in daylight hours between mid-summer and mid-winter is approximately two and a half hours. This variation is more significant than the change in air temperature.