Hawaii Kona Storm Triggered Major Flash Flooding, Power Outages

Serious flooding hit Oahu late Monday, including in the Honolulu area, as a band of heavy rain moved slowly over the island.

A flash flood warning from the National Weather Service (NWS) reported that floodwaters had inundated homes and prompted vehicle rescues and evacuation requests. The flooding had impacted many roads, including the H-1 freeway.

Widespread power outages were also reported in Honolulu after flooding hit a substation, according to an NWS report.

Southerly winds induced by low pressure to the northwest of Hawaii pumped moisture into the state over several days, resulting in bands of heavy rain over the weekend and into the first half of the week.

More than a foot of rain soaked some higher elevation locations on Maui and the Big Island.

The Kona low finally pulled far enough westward to end the heavy rain threat in most parts of the island chain by late Tuesday.

Over the weekend, it was cold enough near the summits of the Big Island’s pair of 13,000-plus-foot mountains - Mauna Kea and Mauna Loa - for snow with this Kona storm.

The National Weather Service issued blizzard warnings for the summits, which then expired Monday morning.

Snow over the Big Island summits is common each year.

Kona Storms and Hawaii's Wetter Season

Hawaii’s usual fair-weather trade winds out of the northeast or east wring out any showers over the windward, or northeast, sides of the islands and mountains.

The trade winds then move down the slopes of mountains and dry out, leaving the west and southwest, or leeward, sides mainly dry.

But a “Kona storm” flips that script, replacing the trade winds with more humid winds from the west or southwest.

When this happens, typically drier leeward locations also get soaked. That's why they're called “Kona storms.” Kona is Polynesian and Hawaiian for leeward.

In fact, these storms provide leeward locations, such as the Big Island’s Kona Coast and Honolulu, with most of their rain.

Kona storms are most common in the cooler time of year, so this is the rainier season in Honolulu.

Hawaii’s capital city picks up almost three-quarters of its average rain from October through March.

But don’t let that scare you away from booking a winter getaway. Even in Honolulu’s wetter season, the city averages only eight to nine days with rain each month from October through March.

So it’s very unlikely your entire trip would be a washout. Just know that you might need to pack a rain jacket for a winter getaway to paradise.