Hurricane Iselle was expected to pass overnight across the Big Island, one of the least populated islands that is known for coffee fields, volcanoes and black sand beaches, then send rain and high winds to the rest of the state on Friday. The storm's predicted track had it skirting just south of the other islands.
Forecasters were analyzing storm data before making possible changes to its categorization, National Weather Service meteorologist Eric Lau said.
"But we're not really too concerned about the track or the intensity of the system," Lau said. "We're primarily urging residents to still take proper precautions to prepare themselves to keep everyone safe."
Hundreds of people flowed into emergency shelters set up at high schools on the Big Island, one of which lost power. Crews worked to restore electricity to the shelter in Pahoa with at least 140 people.
Power also was lost Thursday evening in two communities on the Big Island: Waimea, a town of about 9,200 people near the island's north shore, and Puna, a district scattered with residents south of Hilo, Hawaii County Civil Defense officials said.
Mayor Billy Kenoi said that no major injuries or damage from the first bits of wind and rain have been reported.
People got ready for the storm by making last-minute trips to the store and boarding up windows at their homes.
"It's getting more windy, and it's raining pretty good," said Denise Laitinen on the Big Island. "But I'm ready for it. Everything outside is secured, and I've boarded up the picture windows. I feel good about being prepared for anything these storms bring us."
Meanwhile, Hurricane Julio, strengthened into a Category 3 storm and followed Iselle's path with sustained maximum winds of 115 mph. It was about 1,000 miles behind Iselle and projected to head just north of the islands sometime early Sunday morning.
Hawaii has been directly hit by hurricanes only three times since 1950. The last time Hawaii was hit with a hurricane or tropical storm was in 1992, when Hurricane Iniki killed six people and destroyed more than 1,400 homes in Kauai, Lau said.
Hawaii Gov. Neil Abercrombie said the state is prepared for the back-to-back storms, noting the National Guard is at the ready and state and local governments were closing offices, schools and transit services across Hawaii.
State Attorney General David Louie promised that Saturday's primary elections, including congressional and gubernatorial races, will go forward as planned.
As residents prepared for the possible one-two punch of storms, a 4.5-magnitude earthquake struck the Big Island but didn't cause major damage. There were no reports of injuries.
Kelsey Walker said the quake felt like a "little jolt" but didn't knock things off shelves at the Waimea grocery store where he works.
"We have a hurricane. Now we have this on top of it. What else?" Walker mused.
Travelers faced disrupted plans when at least 30 flights were canceled Thursday from several airlines, including Delta, United, Air China and WestJet, the Hawaii Tourism Authority said.
American Airlines and US Airways canceled flights in and out of the Big Island and Maui after 6 p.m. Thursday through noon Friday. Commuter airline Island Air canceled some afternoon flights and shut down all operations Friday.
Hawaiian Airlines canceled some interisland flights for Thursday evening and moved its Maui-Los Angeles flight up by nearly five hours. The airline waived reservation change fees and fare differences for passengers who needed to alter their plans Thursday and Friday.
After high winds hit Maui, California couple Rudy Cruz and Ashley Dochnahl left the island earlier than planned, getting to Oahu but failing to secure a flight back home.
"We were trying to beat it, but we now will have to ride it out," Cruz said.
Passengers at the Honolulu International Airport spilled out to the curb Thursday, and lines wrapped around the TSA screening area. But some travelers remained optimistic.
Washington state couple Tracy Black and Chris Kreifels made plans to get married in an outdoor ceremony on the Big Island on Saturday. They spent this week getting a marriage license, adjusting plans and communicating with worried guests on the mainland.
"We see the rain as a blessing," Black said. "It will work out as it's supposed to."
The storms are rare but not unexpected in years with a developing El Nino, a change in ocean temperature that affects weather around the world.
Ahead of this year's hurricane season, weather officials warned that the wide swath of the Pacific Ocean that includes Hawaii could see four to seven tropical storms this year.