Hawaii Governor Josh Green warned residents to brace for “an incredible amount of water”.
“Damaging winds, heavy rain, flash flooding and dangerous surf are possible across the state through the weekend,” he posted on X.
Dozens of flights have been cancelled.
At Ellison Onizuka Kona International – Big Island’s largest airport – 40% of flights were grounded, according to flightaware.com. Some 80% of flights were called off at its other main airport, Hilo International.
The more dire forecasts from the National Weather Service (NWS) have been issued for areas within Big Island’s south-east.
“Major rainfall flooding may prompt many evacuations and rescues,” the NWS said, adding that rivers and tributaries “may rapidly overflow their banks in multiple places”.
Nearly 37,000 customers had lost electricity on Hawaii as of Saturday afternoon, according to the website poweroutage.us.
Meteorologist Jennifer Myers, who lives in Hilo, eastern Big Island, said landslides had already cut off some roads, while power lines had been ripped down by falling trees.
“I’m looking at the river right now, and it’s really, really high,” she told the BBC about the view from her apartment of the Wailuku River as it meets Hilo Bay.
“The bay that’s usually blue is like blood red right now because of all the sediment and river water in it.”
