The rain-drenched Hawaiian Islands are bracing for another deluge on Thursday, less than a week after the record-breaking storm closed roads and destroyed buildings.
More than 5 feet of rain fell in parts of Maui from March 10 to 16, according to the University of Hawaii’s climate data team. About 33 centimeters fell in just 24 hours in the Haleakalalā crater, near the top of the island.
Although the next storm is weaker than previous ones, National Weather Service forecasters said it won’t take much to restart the flood. Much of Hawaii is under a flood watch.
“Given the high ground loading from the recent storm, even moderate rainfall levels could pose a risk of flash flooding and flooding,” NWS forecasters said on Thursday.
A Kona storm is a Hawaiian weather pattern that can cause heavy rain in the normally dry, fertile areas of the islands that are normally protected from such rain. The rain expected this week comes from a new corner storm.
These hurricanes interact with a different type of disaster in Hawaii – wildfires – with compounded effects. The island regions hit by heavy rains from the Kona hurricanes are regions where wildfires have become more common over the past few decades. When rain hits fire-affected areas, it causes runoff and erosion, worsening flooding and increasing the risk of mudslides.
Lahaina, where more than 100 people died in the 2023 Maui wildfires, was one of the hardest hit areas in recent flooding. Joseph Pluta, a resident of Lahaina who lost his home in the fire, said debris was flowing over the burn scars.
“All that waste is flowing down the river into people’s homes, into the sea and onto the roads. It’s a real mess,” said Pluta.
The heavy rain in Hawaii came amid a period of crazy weather across the US: Temperatures in California and Arizona broke records Wednesday and Thursday in continued heat, rising into the 90s and triple digits in some areas. Earlier, heavy snow hit the Northeast and Nebraska saw some of its worst wildfires on record.
Hawaii, of course, is prone to rain, but most of it is produced by something called “orographic lift,” when trade winds blow over mountainous island terrain. Air is forced upwards, where it cools, condenses into clouds and brings rain. Most of the time, the winds are from the northeast and the mountains of Hawaii keep most of the rain on that windward side.
“We have upwind areas of about 400 centimeters a year,” said Thomas Giambelluca, a senior professor at the University of Hawaii at Mānoa.
In contrast, the southern and western parts of the islands generally remain relatively dry.
Kona’s storms, however, throw that idea back. Hurricanes form due to 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 surrounds the jet stream and anchors northwest of the islands, drawing tropical moisture toward Hawaii. The wind is blowing from the south, bringing heavy rain to areas that are usually protected from the rain.
Last weekend’s tornado set daily rainfall records in four jurisdictions, according to the National Weather Service in Honolulu.
Laksmi Abraham, spokeswoman for Maui County, said the impacts are “unlike anything we’ve experienced in our lifetime.”
Kona hurricanes hit parts of Maui where wildfires have grown more frequently and more intensely. The practice of fire is associated with an increase in grass that cannot be grown in the area and is highly flammable, especially in damaged areas that were once used for sugar and pineapple plantations.
Clay Trauernicht, a wildland fire expert at the University of Hawaiʻi at Mānoa, has warned for years about the dangers of this uncultivated grass. The Lahaina fire of 2023 made the issue impossible to ignore.
But people don’t realize, says Trauernicht, that fires and floods are inextricably linked.
Flooding can encourage the growth of unusual grasses. Later, when drought strikes, they die.
“What they’re doing is adding fuel,” said Camilo Mora, a climate scientist and professor at the University of Hawaiʻi at Mānoa.
At the same time, rain runs down newly burned slopes quickly, which can cause severe flooding, Trauenicht said. And in areas full of unburned grass, the water table is shallower than in natural forests and less absorbent.
“The root structure of grasses tends to be more of these compact, shallow roots,” Trauernicht said. “You get more water running over the land.”
Places like Lahaina, Trauernicht said, are “highly vulnerable given their fire history.”
Many areas were subject to flooding even before the fire crisis worsened. Parts of South Maui are in federally designated areas, including parts of Kihei, where a condo 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 is working to rehabilitate drainage systems and make local infrastructure more resilient, but the latest storm wouldn’t disrupt any plans.
“Designing an infrastructure capable of completely eliminating flooding during severe storms such as the recent low-lying one would require an extraordinarily large and expensive project that would not be financially feasible,” Molina said in an email.
On Wednesday and Thursday, the Department of Public Works is repairing equipment, working to clear debris from roads and inspecting drains that may be damaged before the next storm arrives Thursday night.
“It’s touching — we’re ready for a flood,” Giambelluci said. “Having this back to back would be terrible.”
