Hurricane Lala brought destructive winds and heavy rainfall to Hawaii's largest island, the Big Island, officials said.
Nearly 130,000 electricity customers across the Big Island and neighbouring islands were without power overnight into Sunday, according to data from the US website Poweroutage.us.
Local media reported downed trees, road closures and severe flooding on the Big Island, which has around 200,000 inhabitants.
Hawaii Governor Josh Green warned residents to stay off the roads. One person was killed in a car accident in the south of the Big Island.
The situation became particularly dramatic late on Saturday evening, as the National Weather Service (NWS) declared a flash flood emergency for parts of the island.
Police said several houses had been swept away by floodwaters, while the weather service warned of a life-threatening and "catastrophic" flood situation.
Green said on Saturday afternoon that 19 roofs had been torn off buildings by the hurricane.
The centre of the Category 1 hurricane passed around 90 kilometres south of the island, heading westward, the US National Hurricane Center (NHC) reported. It was later downgraded to a tropical storm.
The NHC said it expected a total of 30 to 50 centimetres of rain on the windward sides of Big Island over the course of the storm. However, some measuring stations had already exceeded those amounts, with nearly 65 centimetres recorded in Laupahoehoe within 36 hours.
A risk of flooding, landslides and dangerous surf remained, the NHC said.
Dangerously strong winds and heavy rainfall also threatened the state's smaller islands - including Maui, Oahu, Kauai and Niihau - through Sunday, despite their greater distance from the storm's centre.
A flood warning remained in place for Oahu, Kauai and Niihau until late Sunday, with up to 20 centimetres of rain forecast in places.
A Category 1 hurricane, on a scale of 1 to 5, can bring sustained winds of up to 153 kilometres per hour.