As the two hurricanes churned toward the islands, a magnitude-4.5 earthquake hit Hawaii's Big Island at about 6:30 a.m. local time, the U.S. Geological Survey reported.
The temblor struck on the island's north tip, about 7 miles from Waimea. There were no immediate reports of damage.
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. He was trying to keep a sense of humor about it.
"We have a hurricane. Now we have this on top of it. What else?" said Walker, second assistant manager at Foodland Waimea.
Meanwhile, state officials were assuring the islands were ready for the storms and people should prepare but not panic.
Travelers got their first word of disrupted flights Thursday, when commuter airline Island Air said it was canceling some afternoon flights between the islands and shutting down all operations Friday.
Hurricane Iselle was expected to arrive on the Big Island on Thursday evening, bringing heavy rains, winds gusting up to 85 mph and flooding in some areas. Weather officials changed their outlook on the system Wednesday after seeing it get a little stronger, giving it enough oomph to stay a hurricane as it reaches landfall.
"What ended up happening is the storm has resurged just enough to keep its hurricane strength," said Mike Cantin, a National Weather Service meteorologist.
Cantin said that means stronger winds of 60 to 70 mph, though rainfall estimates of 5 inches to 8 inches in a short time frame remained unchanged.
"Not a major hurricane, but definitely enough to blow things around," he said.
Iselle loomed about 400 miles east of Hilo early Thursday, with sustained winds of 85 mph and traveling about 18 mph.
Cantin said the Big Island's size and terrain would help break up the hurricane, weakening it into a tropical storm as it passes Maui and Oahu late Thursday and early Friday.
Hurricane Julio, meanwhile, swirled closely behind with maximum winds whipping at 100 mph. The National Hurricane Center said it expected the storm to strengthen even more Thursday before gradually weakening by Thursday night. That weakening is expected to continue into the weekend.
Hawaii has been directly hit by hurricanes only three times since 1950, though the region has had 147 tropical cyclones over that time. The last time Hawaii was hit with a tropical storm or hurricane was in 1992, when Hurricane Iniki killed six people and destroyed more than 1,400 homes in Kauai, said meteorologist Eric Lau.
The two hurricanes have disrupted tourism, prompted flash flood warnings and led to school closures. Gov. Neil Abercrombie, meanwhile, signed an emergency proclamation allowing officials to tap into a disaster fund set aside by the state Legislature.
Hawaiian Airlines waived reservation change fees and fare differences for passengers who needed to alter travel plans Thursday and Friday because of the storms. Hawaiian Airlines spokeswoman Ann Botticelli said hundreds of inquires poured in from customers seeking to change their flights.
Some travelers remained hopeful.
Boston resident Jonathan Yorke and his wife booked a Hawaii vacation with their two daughters last year. He has been watching the news to see how the storms could affect the two-week trip to Maui and the Big Island.
"We're all optimists, so we'll make the best of it," Yorke said.
Washington state couple Tracy Black and Chris Kreifels made plans to get married in an outdoor ceremony on the Big Island Saturday. They spent Wednesday 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."
It wasn't immediately clear what financial impact the storms would have on the state's tourism industry, a key economic driver.
Hawaii residents also have had to adjust. Stores have seen long lines this week as people brace themselves.
Some are voting early in primary elections that close Saturday. The elections include several marquee races, including congressional and gubernatorial races. Abercrombie - who is running for re-election in a tight Democratic primary - said the election is expected to move forward as planned as of Wednesday afternoon.
Also, education officials said public schools on the Big Island, Maui, Molokai and Lanai will be closed Thursday.
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 cyclones this year.
Associated Press writers Doug Esser in Seattle, Oskar Garcia in Honolulu, Karin Stanton in Kailua-Kona, and Dan Joling in Anchorage, Alaska, contributed to this report.