The first hurricane expected to hit Hawaii in 22 years weakened slightly Thursday as its outer edges began to bring rain and wind to the Big Island, while residents and tourists prepared for a possible one-two punch as another major storm lined up behind it in the Pacific.

The eye of Hurricane Iselle was about 400 kilometres southeast of Hilo, moving at roughly 27 km/h and expected to make landfall Thursday evening, according to the National Weather Service.

Meanwhile, Hurricane Julio strengthened early Thursday into a Category 2 storm but was forecast to pass just north of the islands sometime Sunday morning.

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. Emergency shelters also are being opened across the state.

Meanwhile, state Attorney General David Louie promised that Saturday's primary elections will go forward as planned.

Airlines cancel flights

Earlier Thursday, a 4.5-magnitude earthquake struck the Big Island but didn't cause major damage. There were no reports of injuries as residents made last-minute trips to grocery stores and boarded up their homes.

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A resident of Hawaii leaves a local hardware store with sheets of plywood to board up his windows as two hurricanes approach the islands. (Hugh Gentry/Reuters)

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 humour about it.

"We have a hurricane. Now we have this on top of it. What else?" Walker mused.

Travellers got their first word of disrupted plans Thursday, when commuter airline Island Air said it was cancelling some afternoon flights between the islands and shutting down all operations Friday.

More airlines have since cancelled flights.

American Airlines and US Airways have cancelled all flights leaving or going to the Big Island and Maui after 6 p.m. local time Thursday. They expect flights to resume at noon Friday.

Hawaiian Airlines has halted Thursday evening inter-island flights in Hilo, Kona and Maui. It also moved its Maui-Los Angeles flight up by nearly five hours.

The Hawaii Tourism Authority says United Airlines also cancelled flights, but the carrier couldn't immediately be reached for comment.

Airports remained open Thursday, but the Department of Transportation encouraged travellers to check with airlines. Travellers were urged to stay in hotels instead of heading to the airport, unless their flight was imminent.

"It's very, very important that people understand that our airport is not set up to handle large crowds," Ford Fuchigami, interim director of the Hawaii's Department of Transportation, said in a press conference.

Public bus service on Oahu and Maui was shutting down bus service Friday. In Oahu, evacuation buses would start running late Thursday.

The U.S. Coast Guard shut down ports on the Big Island, Maui and Oahu, arranging for barges and ships to leave the ports and seek sheltered waters.

"I am committed to reopening each port as soon as it is safe to do so," Capt. Shannon Gilreath said in a statement.

Canadians warned about storm risk

Hurricane Iselle was expected to bring heavy rains, winds gusting up to 137 km/h and flooding in some areas, but officials said the Big Island's mountainous region and size should help break apart and weaken the storm as it passed on to Maui and Oahu late Thursday and early Friday.

"Not a major hurricane, but definitely enough to blow things around," said meteorologist Mike Cantin of the National Weather Service.

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Canadian tourists were warned against non-essential travel to Hawaii due to the hurricane risk. (Hugh Gentry/Reuters)

Hawaii has been directly hit by hurricanes only three times since 1950, though the region has had 147 tropical storms over that time.

The last time Hawaii was hit with a hurricane was in 1992, when Iniki killed six people and destroyed more than 1,400 homes in Kauai, meteorologist Eric Lau said.

The twin hurricanes have disrupted tourism, prompted flash flood warnings and led to school closures.

Hawaiian Airlines waived reservation change fees and fare differences for passengers who needed to alter their plans Thursday and Friday.

Canadians on Wednesday were told to avoid non-essential travel to Hawaii because of the storms.

"Canadians seeking emergency consular assistance in the area should contact the Consulate General of Canada in San Francisco or the Emergency Watch and Response Centre in Ottawa," the department said on its website.

Hawaiian Airlines said it will waive reservation change fees and fare differences for passengers who need to alter travel plans because of the storms. The airline said fees will be waived for those who are ticketed to travel on Thursday and Friday. They will be allowed to change reservations for flights through Aug. 12.

‘Everybody’s heeding the warnings’

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."

Some residents, meanwhile, are voting early in the primary elections that include congressional and gubernatorial races.

"It's quiet, nobody's around right now. It's kind of eerie" said Hilo resident Kimo Makuakane. "Everybody's heeding the warnings -- staying at home and staying indoors."

Education officials said public schools on the Big Island, Maui, Molokai and Lanai will be closed Thursday.

Winds pick up on Mauna Kea peak

Officials at Mauna Kea Observatories, a collection of 13 telescopes operated by astronomers from 11 countries located around 14,000 feet atop a dormant volcano on the Big Island, said the site was being secured and that visitor stargazing will be cancelled Thursday night.

"It's starting to get gusty on the summit of Mauna Kea," said the observatory's Gwen Biggert.

But the telescopes are in no danger, said Roy Gal, astronomer and outreach specialist for the University of Hawaii Institute for Astronomy.

“We get tropical storms all the time which get comparable winds to a Category 1 hurricane,” Gal said.

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.

With files from CBC News