Hurricane Iselle not slowing near Hawaii

Honolulu - Hawaii prepared Wednesday for what could be the first hurricane to hit in more than 20 years as weather officials said an approaching storm isn't weakening as previously predicted.

Hurricane Iselle had been expected to weaken into a tropical storm before reaching Hawaii's Big Island on Thursday, but officials now say it has intensified and is forecast to maintain hurricane strength or become a strong tropical storm as it approaches.

A second hurricane, Julio, is following closely behind. It is expected to slowly strengthen and pass north of the Big Island sometime over the weekend. The national hurricane centre classified Hurricane Julio as a Category 1 storm, with winds of about 120km/h.

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

The clustered storms are rare but not unexpected in years with a developing El Nino, a change in ocean temperature that affects weather around the world.

Much of Hawaii's archipelago was under a tropical storm watch or warning. Residents were stocking up on essentials, and weather officials asked the whole state to prepare for flash flooding.

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, said Eric Lau, meteorologist for the National Weather Service in Honolulu.

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.

"The central Pacific doesn't see nearly the activity that the Atlantic sees", said James Franklin, chief of hurricane specialists for the national hurricane centre.