Hawaii endured its worst flooding in more than 20 years after heavy rains fell on soil already saturated by downpours from a winter storm a week ago, prompting officials to urge people in hard-hit areas to “LEAVE NOW” early on Saturday. More rain was expected over the weekend.Muddy floodwaters smothered vast stretches of Oahu’s North Shore, a community renowned for its big-wave surfing, as raging waters lifted homes and cars and prompted evacuation orders for 5,500 people north of Honolulu. Authorities also cautioned that a 120-year-old dam could fail, The Guardian reported.“The remaining access road out of Waialua is at high risk of failure if rainfall continues,” an emergency alert said.On the island of Maui, authorities upgraded an evacuation advisory to a warning for some parts of Lahaina, which is still reeling from a deadly 2023 wildfire, because of retention basins nearing capacity.North Shore Oahu residents who did not evacuate were heartened in the morning by receding waters and moments of blue sky, but more rain was on the way.“Don’t let your guard down just yet,” said Tina Stall, a meteorologist with the National Weather Service in Honolulu. “There’s still potential for more flooding impacts.”Racquel Achiu, a Waialua farmer who stayed to care for her livestock, found her goats in knee-high water Thursday night, and an hour later, her family’s seven dogs were in danger of drowning in an elevated kennel. Her nephew and son-in-law rushed out into chest-high water to save them.“My dogs’ heads were literally just sticking out of the water,” Achiu said. “There was so much water, I cannot even express.”Governor Josh Green said the cost of the storm could top $1bn, including damage to airports, schools, roads, homes and a Maui hospital in Kula.“This is going to have a very serious consequence for us as a state,” Green said at a news conference. He also said his chief of staff spoke to the White House and received assurances of federal support.Green said the flooding was the state’s most serious since 2004, when homes and a University of Hawaii library were swamped.Dozens and perhaps hundreds of homes have been damaged, but officials have yet to fully assess the destruction. Some 5,500 people were under evacuation orders.Officials blamed some of the devastation on the sheer amount of rain that fell in a short amount of time on saturated land. Parts of Oahu received 8 to 12in (20 to 30cm), the National Weather Service said.More than 200 people were rescued from the rising waters, authorities said, but no deaths were reported and no one was unaccounted for. Crews searched by air and by water for stranded people.Winter storm systems known as “Kona lows”, which feature southerly or south-westerly winds that bring in moisture-laden air, have been responsible for the deluges in the past two weeks. The intensity and frequency of heavy rains in Hawaii have increased amid human-caused global heating, experts say.Officials have been closely watching the Wahiawa dam, which has been vulnerable for decades, saying it was “at risk of imminent failure”.Water levels in the dam about 17 miles (28km) north-west of Honolulu, on the island of Oahu, receded by late Friday and then went up again with overnight rain.However the dam appeared to be less of a concern the following morning than the “breadth of hazardous conditions” across the island, said Molly Pierce, a spokesperson for Oahu’s department of emergency management.She noted substantial flooding including in residential parts of Honolulu.“We’re seeing the waters receding in a lot of places, but again with that saturation, just the smallest amount of water can bring those raging back up,” Pierce said. “So even if it’s blue skies where you are, I think we all know in Hawaii that if rain is falling on the mountain, it’s coming to you soon enough.”