Hurricane and gale warnings have been posted across the South Pacific nation of Fiji as Tropical Cyclone Winston bears down on the islands this weekend.

The Joint Typhoon Warning Center at Pearl Harbor forecasts Winston to make landfall as a major Category 4 cyclone with sustained winds of 150 mph.

“Expect very destructive hurricane-force winds,” the Fiji meteorological service warned residents in the nation’s eastern islands. The forecast also calls for flooding from heavy rains and storm surge. The storm was generating rough seas with wave heights to 38 feet on Friday, NASA’s hurricane website said.

The National Hurricane Center says with a Category 4 hurricane, “catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”

Winston is expected to hit the southern coast of Taveuni Island around midday Saturday, Fiji time, then move on to the southern coast of Vanua Levu.

“The town of Savusavu and especially the village of Namalata will be severely impacted by Winston,” Accuweather.com said.

On Sunday, the storm should be just west of the main island of Fiji, before turning south and weakening.

Winston initially passed west and south of Fiji before turning back toward the island earlier this week.

“Destructive winds may begin several hours before the cyclone center passes overhead or nearby,” the Fiji agency said.

The Fiji’s Bureau of Statistics says the island nation, which is about 1,000 miles north of New Zealand, had a population of more than 830,000 in its 2007 census. Fiji is made up of more than 300 small islands, only about a third of which are inhabited.

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Bloomberg News contributed to this story.