The US state, still reeling from last year's deadly Hurricane Helene, declared an emergency Tuesday as Erin's impacts were predicted to begin from Wednesday evening through Thursday.

"Based on the current forecast, we are anticipating coastal flooding from massive waves, tropical storm force winds and tidal and storm surge for much of the state shoreline, especially the Outer Banks, from this evening through Thursday," Governor Josh Stein told reporters.

As of Wednesday afternoon, Erin was churning northward some 300 miles southeast of North Carolina, packing maximum sustained winds of 110 mph (175 kph), according to the National Hurricane Center -- with the possibility it could still restrengthen to a major hurricane.

Its unusually large size means tropical storm-force winds extend hundreds of miles from its center, earning it the moniker "Enormous Erin" by hurricane specialist Michael Lowry, who wrote on Substack the US was fortunate to be spared a direct hit.

Erin's low pressure of around 940 millibars at its center is "remarkably low" and a more telling indicator of its destructive potential than wind speed, Lowry added.

Mandatory evacuation orders were issued for Ocracoke and Hatteras Islands. Parts of North Carolina to Virginia were under a tropical storm warning.

Stein urged residents to pack enough food, water and supplies to last up to five days -- and to safeguard important documents like insurance policies.

"We have already pre-positioned three swift water rescue teams and 200 National Guard troops to various locations on the coast, along with boats, high clearance vehicles and aircraft," he added.

- 'Massive' waves -

Highway 12 -- which runs through the scenic Outer Banks, a string of low-lying islands and spits already under threat from sea-level rise and erosion -- could be left impassable by waves as high as 20 feet (six meters).

Last year's Hurricane Helene caused approximately $60 billion in damage to North Carolina, equivalent to almost two years of the state's budget, said Stein, who criticized what he called inadequate federal assistance from the administration of President Donald Trump.

Trump has mused about dismantling the Federal Emergency Management Agency, which has long been a target of conspiracy theories from the political right.

Beyond the flooding risks in North Carolina, nearly the whole of the US East Coast meanwhile is threatened by rip currents, powerful surges that run against the tide.

- Insurance risks -

The Atlantic hurricane season, which runs from June 1 to November 30, has entered its historical peak.

Despite a relatively quiet start with just four named storms so far, the National Oceanic and Atmospheric Administration continues to forecast an above-normal season.

Scientists say climate change is supercharging tropical cyclones: warmer oceans fuel stronger winds, a warmer atmosphere intensifies rainfall, and higher sea levels magnify storm surge.

There is also some evidence, though less certainty, that climate change is making hurricanes more frequent.