What to know about powerful Hurricane Erin as it heads toward the US East Coast

Island communities off the coast of North Carolina are bracing for flooding ahead of the year’s first Atlantic hurricane, Hurricane Erin.

Although forecasters are confident that the storm won’t make direct landfall in the United States, authorities on a few islands along North Carolina’s Outer Banks issued evacuation orders and warned that some roads could be swamped by waves of 15 feet (4.6 meters).

The monster storm intensified to a Category 4 with 140 mph (225 kph) maximum sustained winds early Monday while it started to lash the Turks and Caicos Islands and the southeast Bahamas, according to the U.S. National Hurricane Center in Miami.

Tropical storm warnings were in effect for the southeast Bahamas and the Turks and Caicos Islands, the hurricane center said.

Here is what to know about Hurricane Erin.

Storm surge, high winds expected along North Carolina’s coast

Forecasters say Erin will turn northeast — and away — from the eastern U.S. Still, the storm is expected to bring tropical storm force winds, dangerous waves and rip currents to North Carolina’s coast. That is according to Dave Roberts of the National Hurricane Center. Coastal flooding in North Carolina is expected to begin Tuesday.

Evacuations were being ordered on Hatteras Island and Ocracoke Island along North Carolina’s Outer Banks even though the storm is unlikely to make direct landfall. Authorities warned that some roads could be swamped by waves of 15 feet (4.6 meters).

The orders come at the height of tourist season on the thin stretch of low-lying barrier islands that juts far into the Atlantic Ocean.

There are concerns that several days of heavy surf, high winds and waves could wash out parts of the main highway running along the barrier islands, the National Weather Service said. Some routes could be impassible for several days.

Portions of Highway 12 on Ocracoke and Hatteras Islands are most at risk for storm surge, National Hurricane Center Director Michael Brennan said.

Erin’s outer bands hit parts of Puerto Rico and the Virgin Islands with heavy rains and tropical-storm winds on Sunday.

Potentially devastating impacts

Storm surge is the level at which sea water rises above its normal level.

Much like the way a storm’s sustained winds do not include the potential for even stronger gusts, storm surge doesn’t include the wave height above the mean water level.

Surge is also the amount above what the normal tide is at a time, so a 15-foot storm surge at high tide can be far more devastating than the same surge at low tide.

Fluctuating strength

Erin’s strength has fluctuated significantly over the past week.

The most common way to measure a hurricane’s strength is the Saffir-Simpson Scale that assigns a category from 1 to 5 based on a storm’s sustained wind speed at its center, with 5 being the strongest.

Erin reached a dangerous Category 5 status Saturday with 160 mph (260 kph) winds before weakening. It is expected to remain a large, major hurricane into midweek.

“You’re dealing with a major hurricane. The intensity is fluctuating. It’s a dangerous hurricane in any event,” the hurricane center’s Richard Pasch said.

Lethal summer of floods

Although Erin is the first Atlantic hurricane of the year, there have been four tropical storms this hurricane season already. Tropical Storm Chantal made the first U.S. landfall of the season in early July, and its remnants caused flooding in North Carolina that killed an 83-year-old woman when her car was swept off a rural road.

And at least 132 people were killed in floodwaters that overwhelmed Texas Hill Country on the Fourth of July.

Just over a week later, flash floods inundated New York City and parts of New Jersey, claiming two lives.