Radar from the National Weather Service shows bands of heavy rain over the Hawaiian Islands. 

A slow-moving storm is battering Hawaii with heavy rain, flash flooding and damaging winds, knocking out power for more than 100,000 Hawaiian Electric customers, including parts of Waikiki. Some streets are also underwater.On Friday, flooding concerns intensified on Oahu when the city Department of Emergency Management warned that a dam could fail, potentially resulting in “catastrophic flooding,” according to its emergency alert. The dam was nearing 83 feet, while the maximum level before failure is 90 feet. Officials issued an evacuation warning for the North Shore towns of Waialua and Haleiwa, which was lifted Saturday morning after water levels had stabilized.“This is one of the slower moving storms that we have had in a long time,” Dennis Trotter, meteorologist at National Weather Service Honolulu, told SFGATE over the phone. “It is pretty bad compared to recent events that we’ve had.”Hawaii Governor Josh Green closed schools and state offices ahead of the storm. State Parks, universities and other businesses around the Islands also shut down.The system driving the storm, known as a Kona Low, is not a tropical storm. “Kona Lows are typically slow-moving systems that drive tropical moisture up from the south of Hawaii,” Trotter said. Because the Kona Low system moves slowly, it can produce prolonged rainfall and significant flooding.Trotter noted that conditions over Kauai and Oahu are expected to improve Sunday or Monday. “For the eastern half of the state, which is Molokai to the Big Island, it could still see impacts through Sunday, and the Big Island might still see impacts through Monday,” he said.According to the National Weather Service, the eastern half of the state is currently seeing the heaviest rainfall at “roughly 1 to 2 inches per hour.”Trotter said things may not improve until the middle of next week for the entire state.

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