Definition

A Kona storm (also known as a Kona low) is a seasonal cyclone in the region of the Hawaiian Islands.

Description

Kona storms usually occur in winter. These cold-core cyclones, so termed because their coldest temperatures are found in their centers, typically form due to winds coming from the westerly or southwesterly "kona" direction. (The word comes from the native Hawaiian language. It refers to the leeward direction, as Hawaii's most common winds are the northeasterly trade winds.) Kona storms can bring high winds, heavy rain, hail, flash floods, and snow in high elevations. They pick up moisture from the warm tropical waters that surround Hawaii, then interact with the terrain of the islands to create strong precipitation. This type of storm tends to bring greater rainfall than a cold front storm.

According to media reports, a 1980 Kona storm hit Maui with winds recorded as high as 111 mph. A 2007 Kona storm brought gusts of up to 70 mph to Oahu and drenched the Big Island of Hawaii with up to 11 inches of rain. A 2021 Kona also produced heavy rain and flooding. That storm led to emergency declarations and coated the top of Mauna Kea with up to ten inches of snow. Kona lows occur outside the main flow of the atmosphere. Without jet stream winds to push them away, these storms can persist for several days. While flooding can present dangers, heavy kona rains can also relieve Hawaii's frequent drought conditions.

According to the University of Hawaii's meteorology department, numerical weather prediction models don't always reliably track the development of Kona lows. The models have difficulty simulating the mesoscale structures of the systems, partly because of a lack of data over the central Pacific.