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.

Tropical Storm Erin is still moving quickly westward and is forecast to become a hurricane in a few days over the central tropical Atlantic, the NHC said.

While Erin won't hit the U.S. directly, the storm's biggest impact on the East Coast will be along the Outer Banks of North Carolina, where coastal flood watches, tropical storm watches and storm surge watches are in effect. The storm surge could be as high as 4 feet.

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.

Bill Kelly has the latest NEXT Weather forecast for the Philadelphia region on Tuesday night.