The centre of the storm was predicted to move close to or over portions of the main islands later on Thursday or on Friday, bringing risky surf of 20ft and a storm surge of up to 4ft, forecasters said.
Hawaii's biggest hotels are confident they can keep their guests safe as long as they stay inside, said Mufi Hannemann, CEO of Hawaii Tourism and Lodging Association.
President Donald J. Trump issued a disaster declaration Wednesday, authorizing the Department of Homeland Security and the Federal Emergency Management Agency (FEMA), to coordinate disaster relief efforts with the state.
Hurricane Lane, which was still offshore, already lashed the Big Island with almost 20 inches (50 centimeters) of rain in almost 24 hours and was moving closer, putting it and Maui "in the thick" of the storm, National Weather Service meteorologist Melissa Dye said.
The Big Island reportedly got close to 20 inches of rain in 24 hours.
The National Weather Service says there are heavy bouts of rain on the east of the island and lighter rain in other areas.
"We can't go in because the roads - there's a river of water down there", Hawaii County managing director Wil Okabe said.
Maui County shelters are expected to open Wednesday while shelters on Oahu are scheduled to open Thursday.
Hurricane Lane weakened Friday evening as it headed toward Hawaii.
"Hurricane conditions are expected over some areas of Maui County and Oahu starting Friday and continuing through Friday night". The Big Island is under a tropical storm warning, and the islands of Kauai and Niihau are under a hurricane watch.
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Hawaii Emergency Management Agency Administrator Tom Travis said there's not enough shelter space statewide.
He says those who are not in flood zones should stay home. Aid agencies were also working to help Hawaii's sizeable homeless population, many of whom live near beaches and streams that could flood.
Rear Adm. Brian Fort, commander, Naval Surface Group Middle Pacific, announced Wednesday on Facebook that all U.S. Navy ships and submarines based in Hawaii that were not undergoing maintenance would be moved from the harbor and repositioned so that they could help respond after the storm, should the need arise.
Rear Adm. Brian Fort, commander of the Naval Surface Group Middle Pacific, said Wednesday that all ships not now undergoing maintenance are being moved. All vessels not now undergoing maintenance were being positioned to help respond after the storm, if needed.
All Hawaii-based Navy aircraft will be kept in hangars or flown to other airfields to avoid the storm.
The National Weather Service warned that some areas could see up to 30in before the system passes, with bands of rain extending 350 miles from the hurricane's centre.
The Category 4 storm is not projected to make a direct hit on the islands, but officials have warned that even a lesser blow could do significant harm.
Lane was downgraded on Friday to a Category 1, the lowest ranking on the five-step Saffir-Simpson scale, as it churned through the Pacific south of Oahu, the National Weather Service said. Hurricane conditions, including winds of at least 74 miles per hour, will start there Friday, the Hurricane Center said.
Forecasters say it will move close to or over portions of Hawaii's main islands heading into Friday, bringing risky surf of 20 feet.
"Roads all over are impassable due to extreme flooding", said Hawaii resident Lili Koi on Twitter late on Friday night.
"We are just trying to be cautious and be prepared", she said.
Earlier it was reported that the speed of hurricane lane reaches 250 km/h, gusts of wind can be stronger.