A major cold-season Kona storm system is bringing significant precipitation totals to Hawaii, including up to 25 inches of rain, a foot of mountain snow and hurricane-force winds on the summits of the Big Island. A rare blizzard warning was issued for Mauna Kea, whose nearly 14,000-foot summit was a winter wonderland over the weekend.

Flood watches are up for the entire island chain, with flash flood warnings issued for the middle of the archipelago. Record cool temperatures are also visiting the nation’s 50th state, made to feel cooler by winds gusting up to 50 mph even in the lowlands.

The dichotomous weather will make it technically possible to ski and surf in the same hour for residents of the Big Island.

The weather elsewhere

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Moderate to heavy rainfall was ongoing on western parts of the Big Island, Maui, Lanai and Molokai early Monday, the rain pushing toward Oahu and Kauai as another round of invigorated precipitation worked north and west. Maui and Molokai were under flash flood warnings, as heavy rain with rates topping an inch per hour brought “significant and life threatening flooding in drainages, streams, rivers, roads, properties, and other low lying areas,” the National Weather Service in Honolulu said.

The service warned that “multiple public road closures [were] expected, as well as landslides in steep terrain.” The Kamehameha Five Highway in Molokai remained closed near mile marker 8 “due to mud and debris on the roadway,” it said.

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In its forecast discussion, the Honolulu office employed unusually frank language to warn of the potential for high-impact flooding.

“Rain events of this magnitude can produce catastrophic flooding and affect areas that are typically drier, such as the south and west slopes of each island,” the office wrote. “Some additional impacts include dangerous driving conditions due to near zero visibility. Many roads could become impassable due to severe runoff and flooding. Numerous landslides are also expected in areas with steep terrain. Debris in streams and gulches may clog bridges and culverts resulting in dangerous flooding.”

Rainfall totals of 15 to 25 inches are possible by Tuesday evening, with the bulk of the rain falling in a 12-hour window as the main band of rainfall works up the archipelago. That means some places could see rainfall rates of 2 to 3 inches per hour. Rainfall reports indicated that up to 11 inches had fallen on Maui and nearly 9 inches on the Big Island.

Kona storms derive their name from a word meaning “leeward,” referring to the direction their winds come from. They are known for bringing cold air, especially at high altitudes. It comes as no surprise that snow is falling atop the 13,796-foot peak of Mauna Kea, the highest point on the volcanic Big Island. The summit was initially expected to received up to a foot over the weekend, with another 4 to 6 inches anticipated through sunrise Monday. Thundersnow is also possible as air is forced up the mountain in an already unstable, or convective (conducive to showers and thunderstorms), environment.

The road to the summit remains closed as wind gusts up to 80 mph loft snowfall to yield near zero visibility. Conditions will improve during the daylight hours Monday as the band of heavy precipitation shifts west. The blizzard warning in effect over the weekend, the first since 2018, was lifted Monday morning and replaced with a winter weather advisory. The Weather Service said up to 4 inches of additional snowfall was possible on Mauna Kea and Mauna Loa, above 12,000 feet.

While freezing temperatures are relegated to only the tallest peaks above 14,000 feet, according to weather balloon observations, conditions at the surface remain anomalously cool. Sunday didn’t make it above 70 degrees in Honolulu – far from conventionally cold, but very cold relative to normal. Honolulu has seen highs of 70 degrees or cooler only 15 times since World War II; Sunday’s high was the coolest since 1979, and the lowest high temperature ever observed during the month of December, according to Thierry Goose, who tracks temperature extremes around the world.

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The temperature at Daniel K. Inouye International Airport in Honolulu is predicted to climb to just 71 on Monday. Hawaii has little variance in temperatures due to its position in the warming and stabilizing waters of the central tropical Pacific.

In addition to temperature and precipitation anomalies, the Kona storm is bringing near-shore waves of up to 30 feet, with beach flooding and erosion likely. The waves are being whipped up by strong winds, which have also prompted a wind advisory.

Winds will abate and inclement weather will wind down late Tuesday into Wednesday, around which point a return to more typical weather is expected.

Kona storms visit Hawaii a couple times every winter on average, according to the Western Regional Climate Center, and they occasionally pack quite a punch. One such system in March delivered up to 20 inches of rain in 24 hours and spurred the issuance of a pair of tornado warnings, the first to be hoisted in Hawaii since 2008.