“I think this would probably be about a Category 3-type hurricane if we were to do some sort of a similar comparison,” he said. “It's on the line of a pretty destructive hurricane.”

Category 3 hurricanes on the Saffir-Simpson scale, which have sustained winds exceeding 111 miles (178 km) per hour, can cause devastating damage to homes, buildings and utilities.

Osiensky said that by Wednesday evening wind speeds were diminishing but water levels would remain high and new surges of floodwaters were expected.

Most of western Alaska is at high risk, from the Yupik Eskimo community of Bethel in the Yukon-Kuskowim delta to the Inupiat Eskimo village of Wainwright on the North Slope, according to the National Weather Service.

But one of the hardest-hit areas so far has been Nome, a former Gold Rush boomtown famous as the end of the Iditarod Trail Sled Dog Race, and surrounding villages.

There, the storm tossed debris onto roads, making driving dangerous, city officials reported. Waves have launched “fist-sized rocks” and logs up to two feet in diameter onto the roadway, officials said.

“These objects would cause injury to any person that was struck,” the city's emergency managers said in a written statement.

Evacuations have been ordered in low-lying parts of Nome and other sites, with residents housed in schools and other public buildings. But large-scale evacuations out of the region are not considered feasible because weather conditions make flying hazardous, a state official said Tuesday.

Nome, with 3,600 residents, is one of the largest cities in western Alaska. The communities spread along the coastline are mostly traditional Native settlements, with a few hundred to a few thousand inhabitants, and no roads linking communities.

The Alaska Division of Homeland Security and Emergency Management set up an incident command to respond to the storm. The U.S. Coast Guard has stationed helicopters and cutters in the region to aid mariners involved in the crab fishery.

The Alaska National Guard activated an operations center at Joint Base Elmendorf-Richardson in Anchorage.

Powerful storms of this magnitude are common at this time of year in the Bering Sea and North Pacific, but this storm is unusual because of its northward trajectory and the lack of sea ice in near-shore areas like Norton Sound off Nome, National Weather Service and other agency officials said.

“Forty years ago, a big storm like this would come through and the sea ice would act as sort of a buffer,” said Mark Serreze, director of the Snow and Ice Data Center.

“The Bering Sea has and always will have these strong storms. What is different now is their potential destructiveness as you lose the sea ice cover,” he added.