Unusual “Kona Low” to bring winter weather to Hawaii

Roads are covered in washouts and debris following a heavy rainstorm in Waikoloa Village on the Big Island of Hawaii on May 11, 2023. More flooding and heavy rain are expected in the coming days.  Image: Weather boy
Roads are covered in washouts and debris following a heavy rainstorm in Waikoloa Village on the Big Island of Hawaii on May 11, 2023. More flooding and heavy rain are expected in the coming days. Image: Weather boy

A Kona Low will batter the Hawaiian Islands, bringing heavy rain, thunderstorms and even snow to parts of the state in the coming days. This system is especially unusual because they typically form in winter, during Hawaii’s typical “wet season” months of October-April. With severe weather approaching, the National Weather Service in Honolulu, Hawaii, has already issued several flood-related warnings for the Aloha State.

Even before the next Kona Low arrives, people across Hawaii are busy cleaning up from the recent flooding. Unsettled conditions and a low southeasterly flow caused flash flooding in windward Oahu on Monday, with numerous rain gauges reporting 6 to 8 inches of rain over the past 12 hours. On the Big Island of Hawaii, thunderstorms moved across the island’s South Kohala district on Friday evening, inundating residential areas such as Waikoloa Village, port areas such as Kawaihae and famous coastal towns with devastating flash flooding.

The Kona Low gets its name from the change in wind direction that occurs when such a storm moves over the Hawaiian Islands. Hawaii is dominated by the trade winds that generally blow from the northeast. However, counterclockwise flow around a Kona low located west of Hawaii results in southwesterly winds over the islands, usually on the leeward or “Kona” side. Kona Lows are most common between October and April. These types of storms suck in abundant moisture from the warm tropical waters around Hawaii; when this moist flow interacts with the island’s steep topography, wringing out moisture, extremely heavy precipitation can occur. Because the wind flow around a Kona Low is atypical, flood rains occur in places that normally do not flood, in tropical downpours that hit the islands from time to time.

Winds will gradually transition to southerly winds as a more unsettled weather pattern develops Tuesday through Friday. The developing Kona Low will increase the chance for heavy rain and thunderstorms on Kauai and Oahu as early as Tuesday morning, before potentially spreading to the remaining islands in the coming days.

The summit of Mauna Kea lies to the left under the sun, while snow-capped Mauna Loa, where lava flowed just a few weeks ago, stands in the background.  Image: Weather boy
The summit of Mauna Kea lies to the left under the sun, while snow-capped Mauna Loa is in the background in this file photo illustrating the snow in Hawaii. Image: Weather boy

According to the National Weather Service office in Honolulu, Hawaii, “A strong Kona Low will develop north of the state and its associated convergence boundary will hit the state heavily during the second half of the week. The moisture line will move into the state Tuesday night into Wednesday, with increasing chances of heavy rain as deep tropical moisture moves in from the south. Wednesday evening, water precipitation levels will likely increase by more than 1.5 inches in parts of the state, and based on the latest guidance, the moisture line is expected to remain somewhere around Oahu and Maui County. They add: “Where this moisture line remains from Wednesday through Friday will be the area where flash flooding is likely to occur.”

Although the National Weather Service says there is still some uncertainty about where the convergence boundary will linger due to the potential for significant flooding in leeward areas, a Flood Watch has been issued for the entire state from Wednesday through Friday. This Flood Watch is likely to be extended for selected islands due to another heavy rain shower this weekend.

In addition to heavy rain, significant snow may also fall. Although most people don’t associate the tropical paradise that Hawaii is known for with snow, they are surprised to learn that it does snow in the winter due to the height of the volcanic peaks. Mauna Kea is the tallest of the bunch at 13,803 feet. Maui’s Haleakala is much lower at 10,000 feet. Because of that difference, the island of Hawaii will see snow more often than the lower island of Maui. Just one storm in January 2020 dropped 2 to 3 feet of snow on Hawaii Island and created snowbanks that were much deeper. Another storm in 2021 brought snowboarders and skiers to the mountain by the dozens. A Winter Storm Warning was issued last week due to the threat of wintry weather on Mauna Kea on Hawaii Island.

There are no winter weather-related advisories, watches or warnings in effect for Hawaii at this time, but that could change as the storm approaches. Most of the snow will fall on the higher peaks of Hawaii Island late Wednesday or Thursday.

Hawaii is experiencing an unusual weather pattern. Severe drought occurred on many islands as a result of the current ENSO cycle; However, while long-term forecasts called for more dry conditions, these heavy precipitation storm systems are helping to rebuild precipitation deficits.