Residents on the Hawaiian island of Oahu in the US are contending with the worst flooding the state has seen in more than 20 years as winter storms force thousands to abandon their homes to move to safer ground.

The Pacific island's North Shore — revered by surfers worldwide for the quality of its waves — is being hit worst and forecasters are predicting even more rain over the coming days.

Rivers of muddy water raged across the island on Thursday and Friday, sweeping away cars and homes, washing away roads, and triggering the evacuation of at least 5,500 people north of the capital, Honolulu.

"This is going to have a very serious consequence for us as a state," said Hawaii Governor Josh Green at a Friday press conference.

Green said this week's flooding is the worst to hit Hawaii since 2004.

He estimated damage to private and public property from the storm could exceed $1 billion (€860 million).

"There's no question that the damage done thus far has been catastrophic," added Honolulu Mayor Rick Blangiardi.

Turbocharged 'Kona lows' causing Hawaii flooding?

Hawaii is no stranger to wet winter weather, with so-called 'Kona lows' traditionally bringing wet air this time of year. Experts, however, contend that the weather pattern has become turbocharged by human activity, which they say has increased the frequency and intensity of the storms.  

US National Weather Services (NWS) meteorologists at Kaala, Oahu's highest peak, measured 16 inches (40 centimeters) of rainfall overnight Thursday, while other parts of the island received between 8 and 12 inches.  

On Friday, the NWS issued flood watches for the state and flash flood warnings for the North Shore. Another 6 to 8 inches of preciptation is expected over the coming two or three days according to Mayor Blangiardi.

Dole's Wahiawa Dam 'at risk of imminent failure'

Officials say no deaths have been reported thus far but that roughly 10 people were hospitalized with hypothermia. In all, officials say they have rescued more than 230 residents, including 70 children and adults airlifted from a Catholic youth camp on Friday by the US National Guard and the Honolulu Fire Department.

However, crews say their rescue efforts are being increasingly interrupted by individuals operating drones nearby in hopes of getting pictures and video of the devastation.

Lastly, despite massive official efforts to keep residents safe, another major threat looms.

Authorities on Oahu says that the island's Wahiawa Dam is "at risk of imminent failure," calling it a "high-hazard potential," the breach of which "will result in probable loss of life."

The earthen dam, built by the Dole Food Company in 1906 to increase sugar production, and rebuilt after a collapse in 1921, is nearing absolute capacity say officials.

As of Friday, waters held back by the weak structure had reached some 25.6 meters — just 1.8 meters shy of overflowing — after levels rose by more than 1.5 meters overnight.

Years of concern related to state of dam

State officials have been after Dole to fix the site since 2009. Five years ago, the company was fined $20,000 for failing to address safety concerns.

Dole offered to donate its dam, reservoir and ditch system to the state in exchange for Hawaii agreeing to repair its spillway to meet and maintain dam safety standards.

The state passed legislation authorizing the dam's acquisition in 2023. A state board is due to vote on the issue next week.

In a statement, Dole said Friday, "The dam continues to operate as designed with no indications of damage."

Hawaii regulates 132 dams, which the American Society of Civil Engineers says were mostly built as part of irrigation systems for the sugar cane industry.

On Friday, Oahu's Emergency Management Agency addressed the threat posed by the Wahiawa Dam, ordering 4,000 residents living near the dam to "LEAVE the downstream area NOW!"

On Saturday, residents were again implored to leave various parts of the island and to head to one of the many emergency shelters that officials and local groups had set up as authorities announced that "flash flooding is happening or will happen soon."

Residents have been instructed to carpool when possible to avoid traffic blockages as road on the island become increasingly impassable.

Edited by: Kieran Burke