HATTERAS ISLAND, N.C. -- North Carolina's Outer Banks are bracing for the effects of Tropical Storm Maria, even though the storm is expected to pass the state at least 150 miles offshore.

Officials estimate more than 10,000 people have left the Outer Banks as Maria moves closer.

Maria is slowly moving northward, the National Hurricane Center said, and a storm surge warning is in effect from Ocracoke Inlet to Cape Hatteras.

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Maria was downgraded to a tropical storm on Tuesday afternoon, with maximum sustained winds of 70 mph.

Tropical Storm Maria moved toward North Carolina on Sept. 26, 2017. NASA Sport

Dare County Emergency Management Director Drew Pearson said Tuesday morning that it's impossible to get exact figures on how many people evacuated Hatteras Island after they were ordered to do so. But Pearson said officials think between 10,000 and 12,500 people have left the island ahead of the storm. Hatteras has a year-round population of about 500 people, who are not required to leave.

Schools were closed Tuesday in all of Dare County because of expected tropical storm conditions.

Pearson said the worst conditions were expected Wednesday into Thursday morning. Dangerous rip currents are possible in the ocean for the rest of the week.

The National Weather Service in Morehead City said significant beach erosion is expected north of Cape Lookout. Storm surge between 2 feet and 4 feet is expected, mostly north of Cape Hatteras.

Hyde County officials said Monday they thought about 700 visitors would leave because of the evacuation ordered for Ocracoke Island. Ocracoke has a population of about 1,000 residents.

Maria's maximum sustained winds Tuesday reached near 75 mph. The storm is centered about 210 miles southeast of Cape Hatteras and is moving at 7 mph.

A tropical storm warning is in effect for a swath of the North Carolina coast from Bogue Inlet to the Virginia border.

Meanwhile, officials are calling the devastation in Puerto Rico a humanitarian disaster. Six days after Hurricane Maria hit, millions are struggling for basic necessities like adequate food, water, fuel and electricity. Eighty percent of the island's transmission lines are down, and power may not be restored for more than a month.