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Hawaii drying out after historic December deluge, flooding

Honolulu had its second-wettest day on record, and thousands lost power across the state

By
December 8, 2021 at 2:15 p.m. EST
A pedestrian walks across a flooded street in Honolulu on Tuesday. (Eugene Tanner/AFP)

The Kona storm, which drenched the Hawaiian Islands between Saturday and Tuesday, was finally pulling away Wednesday morning, after producing record-setting rains, flooding and mudslides, mountain snow and historically cool temperatures.

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Hawaii Gov. David Ige (D) declared a state of emergency Monday due to the sweeping impacts of the powerful storm, which will remain in effect through Friday during cleanup efforts.

Some of the storm’s heaviest rain hit Honolulu on Monday, dropping 7.92 inches, its wettest December day on record and second-wettest day observed in any month. The torrents caused numerous instances of flash flooding in the capital city, according to the National Weather Service.

Several people trapped in floodwaters required rescue in Honolulu, and firefighters responded to 90 storm-related calls, NBC News wrote.

“One notable impact was flooding damage to the Iwilei power substation which cut electrical service to Downtown Honolulu businesses and residents,” the Weather Service wrote in a storm summary. Thousands of customers also lost power on the Big Island and Maui.

Rainfall totals swelled into the double digits on Oahu, Maui and the Big Island, where the highest 48-hour amounts were 11.68, 12.86 and 14.26 inches, respectively, according to the Weather Service.

Even heavier rain probably fell on the south-facing mountain slopes on Maui, where the Weather Service estimated more than 20 inches.

The Weather Service described “large flash floods” on Maui, where high water shut down sections of major highways on Monday. In the Maui Meadows subdivision, severe flooding damaged homes and washed away several vehicles, the Weather Service wrote.

Kona storms derive their name from a word meaning “leeward,” referring to the direction their winds come from. As this Kona storm meandered west of the islands for nearly three days, its counterclockwise circulation drove wave after wave of heavy rain inland. As the moist air collided with the south-facing mountain slopes, it was forced to rise, intensifying downpours through a process known as orographic lift.

Some years may pass without a single Kona storm affecting Hawaii, while other winters may feature up to four or five, according to the Western Regional Climate Center. This particular storm was a whopper due to its duration, walloping the islands for three straight days.

On the high peaks of Mauna Loa and Mauna Kea on the Big Island, towering over 13,000 feet, the storm brought heavy snow and strong winds, prompting a blizzard warning over the weekend. Snow is fairly common on these mountaintops, but this was the first blizzard warning issued in the state since 2018.

Webcam views of Mauna Loa and Mauna Kea showed their summits blanketed in snow Wednesday morning.

The white-capped peaks could also be seen by weather satellite looking down on the Pacific Ocean from space:

The cold air tapped by the storm, along with persistent cloud cover, brought historically cool weather even near sea level.

Sunday’s high temperature in Honolulu was 70 degrees. The city has seen highs of 70 degrees or cooler only 15 times since World War II; Sunday’s high was the coolest since 1979, and the lowest high temperature ever observed during the month of December, according to Thierry Goose, who tracks temperature extremes around the world.

As the storm pulled away Wednesday, the Weather Service in Honolulu had discontinued all flood watches in effect for the islands as of 6 a.m. local time.

The forecast for Honolulu calls for mostly sunny skies on Wednesday and a high of 82 degrees.

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