The National Weather Service warns of a “high-impact and potentially life-threatening weather pattern” in Hawaii this week, with torrential rainfall, flash flooding, strong winds, severe thunderstorms and mountain snow.
Through Saturday, “we could easily see over 20 inches in the harder-hit areas, but that’s just a ballpark estimate,” said Laura Farris, a meteorologist at the weather service office in Hawaii.
Greater totals are possible atop the state’s volcanoes, which can measure feet of rain from the biggest storms.
The cause is a strong low-pressure system that will bring two rounds of stormy weather to the state Tuesday through Saturday. These systems are locally referred to as ‘Kona lows,’ and are responsible for Hawaii’s most extreme weather during winter months.
“The high-end potential of this Kona storm is significantly outside the realm of ‘normal’ wet season weather,” the weather service said.
Heavy rain will begin over Kauai on Tuesday morning before reaching Oahu on Tuesday night, prompting the weather service to issue a flood watch for those islands, which is in effect through Saturday afternoon.
A lull in storminess Thursday won’t last long, as “an even stronger disturbance is expected Friday into Saturday with major flooding and damaging winds,” the weather service said. That storm is likely to prompt additional flood watches and warnings for Maui and other Hawaiian islands. About 10 inches of rain is predicted in Honolulu, with 30-plus inches of rain possible atop the state’s volcanoes, through Saturday.
Severe thunderstorms could generate hail and damaging winds, with isolated tornadoes even possible Friday and Saturday. Thunderstorm chances are highest for Kauai and Oahu initially, but the second disturbance over the weekend will raise odds for hail, wind and tornadoes across all islands. Significant snow accumulations are forecast for the summits of the Big Islands.
Hawaii is no stranger to heavy rain, as Mount Waialeale, on Kauai, is one of the wettest spots on Earth and averages nearly 40 feet of rain each year, according to NASA. But rainfall rates are expected to approach 2 to 3 inches per hour within the heaviest bands, too much for even tropical islands to handle without flooding.
This Kona low will have an abundance of moisture to work with. The low’s counterclockwise motion, in tandem with an anomalous clockwise-spinning high-pressure system to the east, will work to draw abundant moisture toward Hawaii from the south. It’s the same area of high pressure responsible for the spring heat wave that’s forecast to grip the Western U.S.
The moisture transport won’t stop upon reaching the island state. It will continue northeastward toward the Pacific Northwest, where a strong Pineapple Express may raise flood danger early next week.
