Hurricane Lane has weakened as it approaches Hawaii but was still expected to pack a wallop, forecasters have said.
The National Weather Service said tropical-storm-force winds could begin as early as Wednesday afternoon on the Big Island.
The hurricane was about 305 miles south of Kailua-Kona and moving northwest toward other islands.
Meteorologist Chevy Chevalier said winds slowed overnight from 160mph to 155mph, prompting a downgrade of the hurricane from a Category 5 to a Category 4.
He added it may diminish to a Category 3 by Thursday afternoon but that would still be a major hurricane.
Mr Chevalier said that by early Friday, the hurricane is forecast to be a Category 2 with winds up to 110mph and the centre located west of Hawaii Island and south of Honolulu.
“We expect it to gradually weaken as it gets closer to the islands,” he said.
“That being said, on our current forecast, as of the afternoon on Thursday, we still have it as a major hurricane.”
With winds to 130 mph, the hurricane could cause catastrophic damage.
Public schools on the Big Island and in Maui County were closed until further notice.
Hawaii Governor David Ige is allowing non-essential state employees on the Big Island and Maui to go on administrative leave.
Employees on Hawaii and Maui islands who work in disaster response as well as in hospitals and prisons are required to report to their jobs, the governor said.
The hurricane was moving at 8mph, meteorologist Melissa Nye said.
“We are starting to see some of the rain show up on the Big Island radar,” she added.
Offshore buoys also detected wave action associated with the storm.
A hurricane watch remained in effect for Oahu and other smaller islands, meaning tropical storm-force winds, excessive rain and large swells could arrive starting on Wednesday.
The central Pacific gets fewer hurricanes than other regions, with about only four or five named storms a year, and Hawaii rarely gets hit.
“Winds tend to steer storms away from there,” said Princeton University climate scientist Gabe Vecchi.
He also said upper level winds, called shear, tend to be strong enough to tear storms apart.
Kauai resident Mike Miranda was 12 when Hurricane Iniki devastated the island 26 years ago.
“A lot of people are comparing the similarities between Iniki and Lane,” he said, recalling Iniki’s turn into the islands was sudden.
“I remember how very little rain fell. But I remember the wind being the strongest force of nature I’ve ever witnessed and probably the scariest sounds I’ve ever heard in my life.”
Mr Miranda said his family is used to preparing for hurricane season.
“A lot of people who moved here and never experienced a hurricane,” he said. “They’re the ones rushing to the store.”