Just four days afterstorms swept Hawaii with flooding rainsand more than 100 mph winds, the islands are bracing for another round arriving March 19 and lingering through the weekend.
Another subtropical cyclone, known asa "kona storm" or "kona low," is formingand forecast to bring more rain and flooding, but without the highest winds of the previous storm, said Matthew Foster, a meteorologist with the National Weather Service in Honolulu.
The heaviest rain is expected on Oahu, Maui and the Big Island, according to weather service reports. "While this storm may not be as strong as last week's kona low, individual areas may be impacted differently depending on where rain bands set up," the weather service added.
The system is forecast to drag moisture over the region into the night of March 19 and into the 20th, Foster said. Then a trough will move into the area and intensify on March 20 and 21.
How do kona storms form?
Kona is the Hawaiian word for leeward, and these subtropical cyclones often form on the west or northwest of the archipelago, considered the leeward side of the islands and typically sheltered from the tradewinds and intense rains.
The low pressure systems are a winter phenomenon, worse some years than others, with origins in a series of planetary waves that move around the globe.
The systems appear every year, but don't always hit Hawaii, said Matthew Foster, a meteorologist with the weather service in Honolulu. "We will see them every year, but it's not every time they hit us," Foster said. "We're a small target in the big ocean. They may be 600 miles to the west or the east."
Winds, rain washed over Hawaii March 13-16
Officials are still working to assess and address damage from the March 13-16 storm that dropped up to four feet of rain on the island of Maui. The winds, blowing at hurricane-speed gusts, took down some of the "power high tension wires that go across mountain ridges," said Steven Businger, a University of Hawaii professor.
Hawaii Electric is still reconnecting people, Businger said. On the Big Island, at least 1,848 customers remained without electricity on March 18, with a total of nearly 2,400 across the archipelago, according toUSA TODAY's outage tracker.
Flooding washed over roads in the islands, eroded a home that washed away and caused sinkholes and other damages, according toHawaii Civil Beat.But no deaths had been reported as of March 18.
Widespread winds, gusting to 50 to 80 mph, were reported across the islands, with even higher gusts in a few locations.
Winds gusted to 135 mph at Kaiaulu Puu Waawaa on the Big Island in the early morning hours of March 14, and to 110 mph at the Mauna Kea Summit the next morning. On Maui, the winds gusted to 108 mph at Kula. On Oahu, the winds gusted to 81 mph at Makapuu Beach and to 78 mph at the historical Schofield Barracks.
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In addition to the winds, rainfall amounts were "astronomical," Businger said.
How did the mid-March kona storm compare to previous storms?
A similar – but worse – kona system occurred in 2006, with seven fatalities, Businger said. The rains started in February and continued through March, with 40 days and 40 nights of precipitation, prompting comparisons to the biblical event associated with Noah.
A La Niña pattern in the Eastern Pacific tends to favor stronger lows, Businger said. The 2006 event happened as a La Nina was fading. So did flooding in April 2018 and March 2021.
Fortunately the end is at least in sight for this event, he said. "I'm quite sure that in two weeks this pattern will have changed or diminished greatly."
"You know, March comes in like a lion and goes out like a lamb," he said, adding the folklore stems from the maximum changes occurring as Earth moves toward its Spring Equinox.
"We are at a time when the sun is increasing in strength more from one day to the next than at any other time of year," he said. The length of day increases the fastest around the equinox, with a peak change in day-to-day solar radiation.
Because temperature gradients at various levels in the atmosphere are a primary source of energy for these storms, when the sun begins to warm the cold air, he said it "steals the thunder" out of the low-pressure system.
Although daily rainfall records were broken at several gauges throughout the islands, only one of three major climate stations – Kahului – has reported record rain so far in March.
Kahului has received 16.36 inches of rain, exceeding its previous 10.9 inch record set in March 1967.
At Hilo, where 11.43 inches of rain has fallen, the standing record for March is 49.93 inches in 1980.
At Honolulu, 10.1 inches of rain has fallen, far below its monthly record of 20.79 inches in 1951.
Could 'kona lows' be affected by climate change?
It's possible that climate change could influence the subtropical cyclones in the future. Warming temperatures could increase the potential for heavier rainfall, Businger said, but so far, Hawaii has been spared most of the worst of the increases in sea surface temperatures seen in other regions, because the ocean currents carry warmer water into other regions.
The state is seeing "two trends that are pretty clear in the data," he said. The islands are getting drier, with higher elevations seeing the dryness faster than the lower elevations; and the state is getting warmer.
Dinah Voyles Pulver, a national correspondent for USA TODAY, writes about violent weather, climate change and other news. Reach her at dpulver@usatoday.com or @dinahvp on Bluesky or X or dinahvp.77 on Signal.
This article originally appeared on USA TODAY:Kona storm in forecast again after 'astronomical' rain in Hawaii