The rain-soaked Hawaiian Islands braced for another deluge on Thursday, less than a week after a record-breaking storm buckled roadways and collapsed buildings.
Some parts of Maui received more than 5 feet of rain from March 10 to 16, according to the University of Hawaii’s Climatic Data Team. In just 24 hours, about 33 inches fell at Haleakala Crater near the island’s summit.
Although the upcoming storm will be weaker than previous ones, National Weather Service forecasters say it won’t take much to restart flooding. Much of Hawaii is under a flood watch.
“Given the high soil saturation from the recent Kona storm, even moderate rainfall rates may pose a risk of flash runoff and flooding,” NWS forecasters said Thursday.
A Kona hurricane is a Hawaiian weather pattern that can produce heavy rains in dry, leeward areas of the islands that are normally sheltered from such rain. Rainfall is expected this week from the new Kona storm.
These storms are interacting with a different type of disaster in Hawaii – wildfires – with compounding effects. Areas of the islands battered by torrential rains from Hurricane Kona have become areas where wildfires have become more common over the past several decades. When rain reaches fire-prone areas, it triggers runoff and erosion, exacerbating flooding and increasing the risk of landslides.
Lahaina, where more than 100 people died in the devastating Maui fires in 2023, was one of the areas hardest hit by the recent flooding. Lahaina resident Joseph Pluta, who lost his home in that fire, said debris was flowing over the burns.
“All the crap is washing down the hill into people’s homes and into the ocean and into the streets. It’s a real mess,” Pluta said.
The intense rain in Hawaii comes amid a period of weather madness across the US: Temperatures in California and Arizona broke records in an ongoing heat wave on Wednesday and Thursday, with highs in the 90s and triple digits in some areas. Earlier, heavy snow hit the Northeast and Nebraska saw its worst wildfires.
Hawaii is, of course, accustomed to rain, but much of it is produced by a phenomenon called “orographic lift,” in which the trade winds hit the mountainous terrain of the islands. Air is forced upward, where it cools, condenses into clouds, and produces rain. Most of the time, the wind is from the northeast, and Hawaii’s mountains keep most of the rain downwind.
“We have windy places that get an average of 400 inches a year,” said Thomas Giambelluca, a professor at the University of Hawaii at Manoa.
In contrast, the southern and western parts of the islands are generally relatively dry.
However, the Kona Storms throw that logic into reverse. Hurricanes form as a result of changes in the jet stream – air currents that flow from west to east at higher altitudes. During a Kona hurricane, a low pressure system turns from the jet stream and sets up northwest of the islands, drawing a plume of tropical moisture toward Hawaii. Winds blow from the south, bringing heavy rain to areas normally sheltered from rain.
Last weekend’s Kona storm set daily rainfall records at four official sites, according to the National Weather Service in Honolulu.
Maui County spokeswoman Lakshmi Abraham said the effects were “unlike anything we’ve experienced in our lifetime.”
The Kona hurricanes are hitting parts of Maui where wildfires have grown more frequent and intense. The fire trend is related to the spread of non-native and highly flammable grasses, especially in fallow landscapes once used for sugar and pineapple plantations.
Clay Traurnicht, a wildland fire expert at the University of Hawaii at Manoa, has warned for years about the dangers of these untamed grasses. The Lahaina fire of 2023 made the problem impossible to ignore.
But people still don’t realize, Traurnicht said, that fires and floods are inextricably linked.
Floods can stimulate non-native grasses to grow. Then they die when there is a drought.
“What they’re doing is adding fuel,” said Camilo Mora, a climate scientist and professor at the University of Hawaii at Manoa.
At the same time, rain can flow more quickly from recently burned slopes, which can cause more severe flooding, Traunicht said. And in areas filled with unburned invasive grasses, the water table is shallower and absorbs less than native forests.
“Grass root formation is more favored in these matting, shallow roots,” said Traurnicht. “You run more water on the surface.”
Places like Lahaina, Trauernicht said, are “more vulnerable given their fire history.”
Many areas were flooded before the fire problem escalated. Parts of South Maui are in federally designated flood zones, including parts of Kihei where a condo building collapsed and roadways failed during recent storms, according to Hawaii News Now.
Jordan Molina, director of Maui County’s Department of Public Works, said the county is working to overhaul the drainage system and make the area’s infrastructure more resilient, but the recent storm will strain any system.
“Designing infrastructure capable of completely eliminating flooding during extreme storm events like the recent Kona Low would require an extraordinarily large and expensive system that would not be economically feasible,” Molina said in an email.
On Wednesday and Thursday, the Department of Public Works is demonstrating equipment to clear debris from roads and check drains for blockages before the arrival of the next storm Thursday night.
“It’s related — we prioritized flooding,” Giambellucci said. “Having it back to back could be worse.”
