Hawaii Governor Josh Green warned residents to brace for “an incredible amount of water”.
He said on X: “Damaging winds, heavy rain, flash flooding and dangerous surf are possible across the state through the weekend.”
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”.
Residents were repeatedly urged by officials to prepare for the storm early.
Local message boards on Facebook show residents filling bags with sand to protect their homes and inquiring whether stores remained open in the early hours on Saturday.
Hawaii County’s Civil Defense Agency said public shelters were available in every county on Big Island.
“At this time, you should have completed your storm-ready preparations and focusing on your Sheltering Plan,” the agency said on X.
Iniki, a powerful category four storm, was the last hurricane to strike Hawaii back in 1992.
It caused six deaths and $3bn in damage after making landfall on the southern coast of Kauai.
