HONOLULU – A Kona Low is soaking much of Hawaii this week with heavy tropical rainfall and occasional strong thunderstorms, putting a damper on the usually sunny paradise and triggering flash-flood concerns.
Flood Watches cover the entire state through Thursday as several inches of rain is expected to fall into the weekend from the persistent soggy pattern. The heaviest rain is expected on the southern-facing windward slopes as the area of low pressure draws in surges of tropical moisture from the south.
The Kona Low, which will be weak at first, will drift slowly eastward toward Kauai through Wednesday, according to the FOX Forecast Center. Rain is increasing over the western half of the state on Wednesday, with 1-3 inches already falling in western Kauai and more than a half-inch around Honolulu on Oahu. Heavy rain and thunderstorms remain in the forecast for this first round, with rain impacts mainly over Kauai County and Oahu.
Another Kona Low will drop in from the northwest through the day Wednesday and set up just west of Kauai by Thursday, the FOX Forecast Center said. This second low is stronger than the first one, with deeper southerly winds that will draw up more significant tropical moisture into the eastern half of the state.
What’s more, with the Kona Low bringing a reversal of winds from the typical northeasterly trade winds, areas that are typically rain-shadowed will instead take the brunt of the rainfall.
“The Kona Low is going to set up just to the south and west of (Hawaii), and the counterclockwise rotation changes the wind direction that Hawaii’s not typically used to,” FOX Weather Meteorologist Craig Herrera explained. “And it brings along rain into the islands – especially in the parts of the islands that get the rain-shadow effect.”
This unstable tropical moisture will spread periods of showers, heavy at times, and potentially strong thunderstorms with gusty winds across all islands from Thursday through Saturday.
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Honolulu could pick up a few inches of rain through Saturday. The Big Island of Hawaii, including Hilo, could also see 2-3 inches of rain in the lower elevations, though rainfall totals could reach 8-12 inches or more along the Big Island’s volcano. The rain is forecast to refocus on the western islands from Friday into the weekend.
With recent extreme drought conditions – especially on the leeward sides of the islands – the region is ironically more prone to flash flooding, says KHON-TV Meteorologist Chevy Chevalier.
“These Kona Lows tend to stick with us for quite some time,” Chevalier told FOX Weather. “So, I’d say flooding is our biggest concern, especially, you know, a lot of heavy rain on top of that dry ground, like water on a dry sponge. It tends to run off and give you flash flooding a lot faster.”
In addition, gusty winds combined with freshly saturated soils could lead to downed trees and power lines.
“When we get any kind of winds with saturated grounds, we get trees falling, and we get power lines down quite a bit,” Chevalier said.
The National Weather Service said flood-prone roads and low-lying areas may need to be closed due to the elevated runoff and overflowing streams. In addition, the NWS warned that urban areas may receive more significant flooding and property damage due to the rapid runoff.
Conditions should begin to improve early next week as drier air moves in and the trade winds return.
Maui officials are closely monitoring the storm and its potential impact over the burn-scar areas of Lahania from the deadly fires on Aug. 8.
“Since the fires from August 8th, that area, Lahaina and leeward, portions of Maui especially, everything’s gone,” Chevalier said. “And the problem there is when you get heavy rain, there’s really no buildings and the sewer systems are clogged and you get a lot of runoff fast. They don’t need that.”
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The fire burned homes, commercial buildings, cars, asbestos and plastics, which released toxic substances. The ash and soil are contaminated. Flash flooding can wash the toxins into the ocean and water supplies.
“But they did a great job of cleaning up the toxic waste. They got most of it out of there,” Chevalier explained. “So we think there will be minimal impacts when leeward portions of Maui start to get the heavy rain.”
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Maui officials say a cutting-edge filtration system was installed in the fire’s aftermath to capture, reduce and filter pollutants from stormwater runoff.
“They barricaded it out of the ocean to protect the ecosystem there, too,” Chevalier said.
Kona Lows have had a history of trouble with Hawaii with their tropically infused downpours overwhelming the state with torrential rain and sometimes damaging wind gusts.
A Kona Low that struck in December 2021 dropped 2 feet of rain in Maui, washing some cars away. On Oahu, strong winds at Honolulu’s airport blew a shed into parked planes, damaging the aircraft.
At Mauna Kea’s summit, wind gusts over 100 mph created whiteout conditions, blowing around the 10 inches of snow that fell during the storm.
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Meanwhile, back in 2018, a Kona Low dropped a record-setting 49.69 inches of rain in 24 hours over Waipa Gardens on Kauai on April 14-15.
Easing the drought is the silver lining to the flood threat for Hawaii.
REMOTE HAWAII WILDFIRE COULD LEAD TO NEXT LAHAINA TRAGEDY, EXPERTS WARN
Over 93% of the state is in moderate drought, and 75% is in severe drought, according to the latest U.S. Drought Monitor.