Severe rainfall on Friday led to the largest flood in 20 years on Oahu, Hawaii’s most populous island, forcing evacuation orders and some 200 rescues.
Heavy rain overnight pushed water to just a few feet below the top of a dam in the Wahiawa Reservoir, in northern Oahu, by early Friday morning, leading the island’s Department of Emergency Management to declare the dam at “imminent risk of failure.”
During a news conference on Friday evening, Gov. Josh Green said that water levels in the dam had gone down to 82.68 feet, but that risk remained and a flood warning would remain in effect. The ground is saturated from earlier storms, he said, exacerbating flood concerns from this bout of rainfall.
At 8 a.m., preliminary data from a flood sensor operated by the U.S. Geological Survey showed that water levels in the Wahiawa Reservoir had reached 85.10 feet, surpassing the previous record, 85 feet, which was set in October 2005.
Mr. Green told a local television station that the top of the dam was 90 feet tall, and he called 88 feet “a very critical threshold.” Evacuation is usually ordered when the water level reaches 85 feet, he said.
Storm damage across the Hawaiian islands could cost more than $1 billion in public and private property damage, Mr. Green said. Responders, including the National Guard, had rescued 196 people, and there were no known fatalities. During the evening news conference, the mayor of Honolulu, Rick Blangiardi, said 37 people had been rescued in the previous hour alone. John Bravender, a meteorologist with the National Weather Service in Honolulu, said 10 to 14 inches of rain overnight in Oahu had led to the devastation.
Floodwaters earlier in the day had cut off road access in the area, according to emergency management officials and the Weather Service. Emergency officials urged people in Waialua and Haleiwa to evacuate to higher ground if possible, calling the rising waters “catastrophic.”
The rain bands causing the damage had abated in the afternoon, but they were expected to return by the evening, officials said. Even moderate rainfall is now producing severe flooding because of the saturation, officials said, and storm surges have been coming in at six to eight inches when forecasters projected only two to three.
“We’re doing everything we can to rescue and help people,” Mr. Blangiardi said in the afternoon. “There’s no question the damage done thus far has been catastrophic. It’s hard to say exactly what the damage is because some of the roads have been impassable, but clearly, at the very least, dozens if not hundreds of homes, people being displaced.”
In the afternoon, the governor detailed harrowing rescue efforts for people stuck in floodwaters, including a group of 70 who were surrounded by water at a campsite. It is spring break for public schools in Hawaii, Mr. Green said, and there were many children in the group.
“I was told they are safe right now,” he said. “But they were having difficulty getting out because there was so much water around them.”
In a video posted to social media, he described flooding that had reached “up to chest level” in some areas.
The National Guard has deployed 195 soldiers and airmen to respond and 21 high-water vehicle teams for rescues, officials said Friday evening. The governor also said in the afternoon that the Coast Guard would conduct search-and-rescue operations if needed.
The dam was built in 1906 to supply irrigation water to the Waialua Sugar Company. The dam is owned by Dole Food Company Hawaii, Sustainable Hawaii and Wahiawa Water Company, according to records from the Army Corps of Engineers. Regulators classify it as having a high hazard potential, meaning a failure would probably result in the loss of life, according to the records.
The federal agency also lists the dam’s overall condition as “poor.”
“The aging concrete spillway structure and main embankment integrity are uncertain and may potentially be compromised during a significant flood event,” according to minutes from an October 2023 meeting of Hawaii’s Department of Land and Natural Resources.
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A Dole spokesman, William Goldfield, said in a statement that the company was “working closely with authorities” and continuing to monitor reservoirs. He added that the dam was operating as designed, with “no indications of damage.”
An official with the state Land and Natural Resources Department, Tony Koyamatsu, said that federal and county agencies, as well as emergency responders, would be working together to mitigate risk.
The flash flooding threat came after yet another system delivered heavy rain, only days after a multiday storm brought over two feet of rain to some locations across Hawaii.
“Because the ground was so primed for this storm, we’re seeing things get bad pretty quickly,” said Stephen Parker, a meteorologist with the Weather Service office in Honolulu.
The storm arrived Thursday night and was expected to bring a chance of rain through at least Sunday.
Heavy showers and thunderstorms brought well over a foot of rainfall to parts of northern Oahu in just the last day, the Weather Service said.
In total, the Waialua area, a residential area downstream from the Wahiawa Reservoir, has recorded about 20 inches of rain since last Friday, amid back-to-back storms. One location in the mountains nearby measured nearly 30 inches of rain, according to the Weather Service.
The recent storms are what forecasters call a Kona low. This type of seasonal storm is not uncommon during the rainy season in Hawaii, which runs from November through April, but it tends to bring more rain and move more slowly than typical storms. Such storms can dump heavy rain for extended periods over the same location.
“Last night, north Oahu was in the bull’s-eye of the heavy rain,” Dennis Trotter, a meteorologist with the Weather Service, said on Friday.
State Representative Sean Quinlan said he had been hearing reports that neighbors were looking out for each other, checking in on elders and helping clear streams. Honolulu County, which includes the entire island of Oahu, requires landowners to maintain streams on their properties in part to lower the risk of flooding. People with tractors have been helping with rescues from homes on the North Shore.
Mr. Green said Friday evening that eight hotels in Waikiki are offering rooms at a 70 percent discounted rate. Additionally, five shelters were open. Mr. Blangiardi said that they were prepared to open as many as necessary for the public.
Mr. Quinlan himself was stuck at the Capitol, unable to navigate the roads after a late night of work. Late Friday afternoon, he was waiting on the all-clear to check on his house and on his mother, who does not live in the evacuation zone but is in Sunset Beach, where there is flooding on both sides of her neighborhood, he said.
Jake DiPaola, a 40-year-old North Shore resident, said, “It is the worst flooding I’ve seen in my lifetime.”
“All of our friends are evacuated out of Waialua,” he said. “Our friends that haven’t been evacuated in Haleiwa are on the top floor of their houses, stranded Katrina-style.”
T.J. Cuaresma, whose family has lived on the North Shore for more than 100 years, said that several important bridges in the area had been impassable until midday on Friday.
The damage was made worse by large and small property owners who failed to clear vegetation and other debris from streams, she said. Some property owners along the beach also built driveways with pipes too small to handle heavy flows of water, and planted vegetation that clogs waterways during storms, Ms. Cuaresma said.
Ms. Cuaresma, who was until recently a board member of the North Shore Chamber of Commerce, said that most longtime residents of the area were well prepared for the storm, and that many had evacuated even before formal orders were issued.
In Waikiki, where much of the island’s tourism is concentrated, glum out-of-towners in ponchos strolled the normally bustling beachfront on Friday morning, and a few hardy swimmers and surfers took to the choppy water.
An open-air coffee shop along the beach, Kai Coffee, opened as usual on Friday morning but began flooding and closed before 9 a.m.
“We have not had a rainy season like this in years,” said Eva Harn, a barista there.
Alissa Fa, who lives on the east side of Oahu, where she was born and raised, said the driving wind and rain over the last week had been “the worst I’ve experienced.”
She was impressed by the way the island had prepared, trimming trees to minimize damage and clearing storm drains of debris. But she has still seen trees snapped in half, and many of the windows in her home were leaking. The architectural showroom in Honolulu where she works had closed for most of the past week, and her home lost power for two days.
Friday was Ms. Fa’s 32nd birthday. A year ago, she recalled, she celebrated with friends on the beach.
“That’s not happening this year,” she said with a laugh.
Reporting was contributed by Kurt Streeter, Jack Truesdale and Libby Leonard.