Hawaii braces for more rain as storms take aim at wildfire burn scars

The rain-drenched Hawaiian Islands are bracing for another deluge on Thursday, less than a week after a record storm distorted roads and collapsed buildings.

More than five feet of rain fell in parts of Maui from March 10 to 16, according to the University of Hawaii Climate Data Team. Some 33 inches fell in just 24 hours at Haleakalā Crater, near the island’s summit.

Although the upcoming storm will be weaker than the previous one, National Weather Service forecasters said it won’t take much to restart flooding. Much of Hawaii is under flood watch.

“Given the high soil saturation caused by the recent Kona storm, even moderate precipitation rates could present a risk of rapid runoff and flooding,” NWS forecasters said Thursday.

A Kona storm is a Hawaiian weather phenomenon that can bring heavy rain to generally dry, leeward areas of the islands that are generally sheltered from such precipitation. The rain forecast this week is coming from a new kona storm.

These storms interact with another type of disaster in Hawaii – wildfires – with cumulative effects. The areas of the islands that are being hit by the ferocious rains of Kona storms are the same areas where wildfires have become more common in recent decades. When rain hits fire-affected areas, it triggers runoff and erosion, worsening flooding and increasing the risk of mudslides.

Lahaina, where more than 100 people died in a disastrous fire on Maui in 2023, was one of the areas hit hard by recent flooding. Joseph Pluta, a Lahaina resident who lost his home in that fire, said debris was flowing over burn scars.

“All this crap is rolling down the hills to people’s houses, to the ocean and into the streets. It’s a real disaster,” Pluta said.

The extreme rains in Hawaii come amid a spell of weather madness across the United States: Temperatures in California and Arizona broke records Wednesday and Thursday in a continuing heat wave, with temperatures reaching the 90s and triple digits in some areas. Earlier, heavy snow hit the Northeast and Nebraska saw its worst wildfires.

Hawaii is of course used to rain, but most of it is generated by a phenomenon called “orographic lift,” in which trade winds strike the islands’ mountainous terrain. The air is pushed upward, where it cools, condenses into clouds, and produces rain. Most of the time, winds are from the northeast, and Hawaii’s mountains trap the majority of precipitation on the windward side.

“We have upwind places that get an average of 400 inches a year,” said Thomas Giambelluca, professor emeritus at the University of Hawaii at Mānoa.

In contrast, the southern and western parts of the islands generally remain relatively dry.

The Kona storms, however, reverse this logic. Storms form as a result of changes in the jet stream – currents of air that flow from west to east at high altitudes. During a Kona storm, a low pressure system moves away from the jet stream and settles northwest of the islands, drawing a plume of tropical moisture toward Hawaii. The wind blows from the south, bringing heavy precipitation to areas usually sheltered from rain.

Last weekend’s Kona storm set daily rainfall records at four official sites, according to the National Weather Service in Honolulu.

Laksmi Abraham, a Maui County spokeswoman, said the impacts were “unlike anything we have experienced in our lifetime.”

Kona storms are hitting areas of Maui where wildfires have become more frequent and intense. The fire trend is linked to the proliferation of non-native and highly flammable grasses, particularly on fallow land formerly used for sugarcane and pineapple plantations.

Clay Trauernicht, a wildfire specialist at the University of Hawaii at Mānoa, has been warning for years about the risks associated with these untamed grasses. The Lahaina Fire of 2023 made this problem impossible to ignore.

But people still don’t realize, Trauernicht says, that fires and floods are inextricably linked.

Flooding can stimulate the growth of non-native grasses. Later, when drought hits, they die.

“What they’re doing is adding fuel,” said Camilo Mora, a climatologist and professor at the University of Hawaii at Mānoa.

At the same time, rain runs off more quickly on recently burned slopes, which can cause more intense flooding, Trauenicht explained. And in areas filled with unburned invasive grasses, the water table is shallower than in native forests and less absorbent.

“The root structure of grass tends to be more matted and shallow roots,” Trauernicht said. “You get more water flowing to the surface.”

Places like Lahaina, Trauernicht said, “are very vulnerable given their fire history.”

Many areas were vulnerable to flooding even before the fire problem worsened. Parts of South Maui are in federally designated flood plains, including parts of Kihei, where a condominium building collapsed and roads failed during recent storms, according to Hawaii News Now.

Jordan Molina, director of the Maui County Department of Public Works, said the county was working to overhaul drainage systems and make the area’s infrastructure more resilient, but the recent storm would have put a strain on any system.

“Designing an infrastructure capable of completely eliminating flooding during extreme storms like the recent Kona Low would require an extraordinarily large and expensive system that would not be financially feasible,” Molina said in an email.

On Wednesday and Thursday, the public works department deployed equipment to clear debris from roads and inspect pipes for blockages before the next storm arrived Thursday evening.

“It’s worrying: we are prepared to face flooding,” Giambelluci said. “Having that back-to-back could be bad.”

This article was originally published on NBCNews.com