The Hawaiian Islands typically enjoy a steady, refreshing breeze known as the trade winds, which consistently flow from the northeast for most of the year. However, this dependable pattern occasionally breaks down and gives way to a phenomenon known as Kona winds, signaling an abrupt shift in the island chain’s climate. These unusual winds are a temporary reversal of the prevailing atmospheric flow, pulling warm, moisture-laden air from the south. The arrival of Kona winds brings a distinct change in weather, often transforming the otherwise tranquil conditions into periods of high humidity and turbulent weather.
Defining Kona Winds and Direction
The name “Kona” is derived from the Hawaiian language, meaning the leeward or sheltered side of an island, which is historically the western or southwestern coast. This terminology is deeply rooted in local geography because the winds blow from the direction that is normally shielded from the prevailing trade flow. Kona winds are defined by their direction, specifically a southerly or southwesterly flow across the islands. The shift means that the coasts usually sheltered from wind become the new windward side, experiencing the full force of the altered weather pattern.
The Mechanism of Formation
The existence of Kona winds is contingent upon the temporary breakdown of the dominant Pacific High pressure system, which is the large, semi-permanent weather feature that drives the trade winds. The reversal occurs when a significant low-pressure system, often called a “Kona low” or extratropical cyclone, develops and positions itself typically to the northwest of the islands. Air flows counter-clockwise around the low in the Northern Hemisphere, which pulls air from the tropics toward the Hawaiian Islands from a southwesterly direction. Kona lows are cold-core cyclones that, unlike hurricanes, form outside of the tropics and are most prevalent during the cooler months; intensity and proximity dictate the strength and duration of the resulting Kona wind event.
Environmental and Weather Effects
The most immediate and noticeable consequence of Kona winds is the sudden increase in warm, humid air, which often leads to significant rainfall and stormy conditions, collectively known as Kona storms. As the moist, southerly flow is forced upward by the high volcanic mountains, a process called orographic lifting, the air cools and produces heavy precipitation. This can lead to flash flooding and landslides, especially since the rain falls on areas, like the leeward coasts, that are typically much drier. Kona wind events can also generate powerful, damaging gusts, particularly as the air funnels through mountain gaps or descends the slopes. Wind speeds can exceed 100 miles per hour in localized areas, causing substantial property damage and large ocean swells.
A secondary, but highly impactful, effect is the transportation of volcanic smog, or VOG, which is composed of sulfur dioxide gas and acidic aerosols from Kīlauea volcano. Under normal trade winds, VOG is usually blown southwest, affecting the Kona coast; however, the reversed Kona flow carries the plume directly over the windward side of the Big Island and up the rest of the island chain, significantly diminishing air quality in previously clean areas.
Duration and Frequency
Kona winds are a seasonal occurrence, typically manifesting during the winter period, which stretches from October through April. This is the time of year when the Pacific High pressure system is at its weakest and most susceptible to disruption by migrating low-pressure systems. In an average year, the islands typically experience between two and three significant Kona storm events. These events are generally short-lived when compared to the persistent nature of the trade winds, which can blow for weeks on end. A strong Kona wind episode or Kona low can affect the region for anywhere from a few days to a week or slightly longer.