Double threat ... This NASA Rarth Observatory image shows Hurricane's Iselle (left) and Julio (right).

Double threat ... This NASA Rarth Observatory image shows Hurricane's Iselle (left) and Julio (right). Photo: AFP

A pair of hurricanes bearing down on Hawaii has grounded flights and closed visitor areas while threatening floods, landslides and blackouts during the heart of tourist season.

Hurricane Iselle weakened to 129 kilometers per hour from 137 km/h as it neared the Big Island of Hawaii, where it is forecast to go ashore overnight. The storm was 490 kilometres east-southeast of Hilo as of 5 am local time, the US Central Pacific Hurricane Centre said.

Farther to the east, Hurricane Julio has grown stronger, with top winds reaching 169 km/h, making it a Category 2 storm on the five-step Saffir-Simpson scale, the US National Hurricane Centre in Miami said. It was 1987 km east of Hilo.

Walton Hong leaves a local hardware store with screen doors to prepare his house in Mililani, Hawaii ahead of the hurricanes.

Walton Hong leaves a local hardware store with screen doors to prepare his house in Mililani, Hawaii ahead of the hurricanes. Photo: Reuters

"Iselle is down to a Category 1; it continues to move pretty quickly," said Paul Walker, a meteorologist at AccuWeather in State College, Pennsylvania. "It will be making landfall this evening Hawaiian Standard Time. They will have winds exceeding 120 km/h, especially at the high elevations, and possible widespread and long-lasting power outages."

Starwood Hotels & Resorts Worldwide's storm preparations included shutting off gas lines to outdoor tiki torches and moving food and beverage service indoors, Stephanie Dowling, a spokeswoman for the company, said in an email. It also waived cancellation fees for guests whose travel plans are affected by the storms.

Tourism peak

Andrea Malosa loads bottled water into her shopping cart while buying supplies in Mililani as two hurricanes  approach the Hawaiian islands.

Andrea Malosa loads bottled water into her shopping cart while buying supplies in Mililani as two hurricanes approach the Hawaiian islands. Photo: Reuters

Tourism in Hawaii tends to peak in June, July and August, when schools are shut for vacation, Ken Rewick, vice president of flight operations for Hawaiian Airlines, said by telephone from the company's headquarters in Honolulu.

Island Air scrubbed all flights on Friday and intends to return to its regular schedule on Saturday, the airline said on its website. It is owned by Oracle founder Larry Ellison's Ohana Airline.

The US National Park Service will close its Hawai'i Volcanoes visitor centre and museum at 1 pm Backcountry areas and roads in the area have also been shut in the park that receives about 1.6 million tourists per year. The state's Division of Forestry and Wildlife shut its hiking trails, wildlife sanctuaries and reserves on the Big Island and Maui.

A hurricane warning was issued for the Big Island of Hawaii and its surrounding waters, according to the local National Weather Service office. A tropical storm warning is in place for the rest of the state, as well as a flash flood watch.

Damaging surf

"Very large and damaging surf is expected to rapidly build along east- and south-facing shores today and tonight, especially on the Big Island," the Central Pacific Centre said in an advisory. "The combination of dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising water."

Walker said there's a possibility Iselle will continue to lose strength and strike as a strong tropical storm, still a powerful system.

There's also a chance the volcanoes on the Big Island may weaken Iselle as it approaches, Walker said. The mountains reach 4169 metres, according to the National Park Service.

Julio may drift north and miss the islands over the weekend, according to hurricane centre track forecasts. Computer models show it curving to the north and losing strength as it nears the island chain, Walker said.

Earthquake

As Hawaii braced Thursday for two hurricanes - which would be the first to hit the state in 22 years - a magnitude 4.5 earthquake shook Waimea on the eastern shore of the Big Island, according to the US Geological Survey.

The Pacific Tsunami Warning Centre said some areas may have experienced shaking, but no tsunami was expected. The earthquake hit at a depth of 12.7 km.

There were no reports of damage from the 6:24 am temblor, but the news heightened the concerns of island residents, who have been stocking up on food and water in anticipation of the approaching storms.

Rare cluster

It is rare for two storms to threaten Hawaii so close together.

Storms tend to "come in clusters but this close is not typical," Rewick, said. "Julio seems to be taking a more northerly track, which for the islands is helpful because it gets up into the higher, cooler water and saps the energy out of them."

Only two hurricanes, tropical systems with winds of at least 119 km/h, have made direct strikes on Hawaii since 1949, said Jeff Masters, founder of Weather Underground, in his blog.

One of those was Hurricane Iniki, which struck as a Category 4 storm, killing six and causing $US2 billion ($2.16 billion) in damage in September 1992, Masters wrote. The other was Dot in 1959. Both made landfall in Kauai.

Near Japan, Typhoon Halong, a Category 1 storm with winds of 138 km/h, was moving north 888 km south of Iwakuni, the US Navy Joint Typhoon Warning Centre said.

"It's already bringing heavy rains to Japan and it's moving very slowly, so they are going to get a long period of heavy rains through Saturday," Masters said. "There could be significant flooding damage in southern Japan."

Bloomberg, Los Angeles Times