Hurricane Erin has been downgraded to a Category 3 hurricane but is gaining in size and raising the risk of life-threatening surf later this week along the U.S.

Powerful Hurricane Erin is expected to bring high seas, big rip currents, and rough surf as it moves between the United States and Bermuda.

The storm has already prompted evacuation orders on North Carolina's Outer Banks and warnings about dangerous rip currents and swells along the East Coast.

Storms that ramp up so quickly complicate forecasting and make it harder for government agencies to plan for emergencies. Hurricane Erick, a Pacific storm that made landfall June 19 in Oaxaca, Mexico, also strengthened rapidly, doubling in intensity in less than a day.

The Ocean City Beach Patrol has closed the ocean to swimming, wading and surfing Tuesday as tropical storm activity off the coast brings dangerous conditions to the resort town.

While Tropical Rainstorm Erin continues to generate rough surf and coastal hazards, AccuWeather meteorologists are monitoring additional tropical waves near the region where Erin initially formed earlier this month.

The storm will remain a major hurricane through the middle of the week, according to the National Hurricane Center.

Most of Erin’s intensification occurred during a 12- to 15-hour window overnight, according to Dan Pydynowski, a meteorologist at AccuWeather. By 5 p.m. Friday, Erin’s winds had remained only 75 mph.