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(CNN) -- You'll have to pardon the people of Hawaii if they are freaking out over an approaching hurricane. It's the kind of thing that rarely happens around there.

And there are two headed that way.

There's Hurricane Iselle, which looks like it will smack into the Big Island on Thursday night, and the less threatening Hurricane Julio, due a few days later.

The Central Pacific Hurricane Center in Honolulu issued a hurricane warning for Hawaii County on Wednesday afternoon.

"Tropical storm conditions are expected on the Big Island of Hawaii Thursday, with hurricane conditions expected Thursday night," the center advised. The storm had maximum sustained winds of 90 mph on Wednesday night but Iselle was expected to weaken as it nears Hawaii.

Tropical storm warnings are in effect for the islands of Lanai, Maui, Molokai and Oahu.

Hawaii is a rare target for any tropical cyclone, let alone two.

In Hilo, people were standing on beaches, anxiously looking out at the water.

"The surfers get excited about these storms, but everyone else is freaking out," said Chris Owens, owner of East Side Builders and a longtime resident. "A lot of the locals here believe that the tall mountains on the Big Island shield them from hurricanes, but in 24 hours this theory could be proven wrong."

Customers formed lines from the front to the back of a Cost-U-Less store on Tuesday, clearing shelves of bottled water and stocking up on other supplies.

"A lot of rice, water, toilet paper," store worker Mike Kelley told CNN affiliate KGMB.

Bottled water also was sold out at a Honolulu-area Costco.

"So we're going to bottle up water at home now and just pray for the best," would-be customer Lisa Viela told CNN affiliate KHON on Tuesday.

Jackie Collins joined a steady stream of drivers trying to fill up vehicle gas tanks at the same Costco.

"We came last night, but it was too crowded, so I thought, 'Well, today I'd better go,'" she told KHON.

Not everyone was worried. Scott Murray, who owns the Hilo Surfboard Co. and has lived on the Big Island for more than 60 years, said many residents were more optimistic for good surf than concerned about damage and flooding.

"I'm not really worried about his storm," Murray said.

The schools on the Big Island and Maui will be closed Thursday as residents await Iselle's arrival.

Hawaii's primary elections will go on as scheduled Saturday, despite the storms, KGMB reported. Local media reported that many turned up for early voting in expectation of severe weather on election day. Others are concerned that voter turnout could be affected.

Julio, also churning westward in the Pacific, could potentially brush the islands on Sunday as a tropical storm, forecasters said.

Iselle is expected to bring heavy rain and high surf, which could lead to coastal flooding on islands already saturated by recent rains, the National Weather Service said.

Julio is expected to move north of Hawaii on Sunday, but outer bands of rain and strong winds still could affect the islands.

Hawaii Gov. Neil Abercrombie signed an emergency proclamation, his office said. It gives the government access to the state's disaster funds.

Some airlines are making concessions to customers ahead of the storms. For people who had been scheduled to travel to or from Hawaiian airports on Thursday and Friday, United Airlines and Hawaiian Airlines say they won't charge fees to change reservations, and they'll waive differences in fares for those changes.

Island Air will do the same for passengers ticketed from Thursday though Tuesday. Delta said it would waive fees for reservation changes for Thursday and Friday, but fare increases could apply.

Hawaii doesn't often have to prepare for cyclones. A 2002 report by the U.S. Geological Survey said that "actual hurricane strikes on the Hawaiian Islands are relatively rare in the modern record."

"More commonly, near-misses that generate large swell and moderately high winds causing varying degrees of damage are the hallmark of hurricanes passing close to the islands," according to the report.

CNN's Taylor Ward, Mariano Castillo, Katia Hetter and Tony Marco contributed to this report.