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

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.

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.

The outer bands of powerful Hurricane Erin lashed Puerto Rico, and the storm is approaching the Bahamas next. What can the mainland U.S. expect?

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.

While a Gulf disturbance that moved into Texas on Friday seems to have run its course, Hurricane Erin in the western Atlantic intensifies.

Hurricane Erin will continue to strengthen as it approaches the Leeward Island and Puerto Rico, where it will threaten with tropical downpours, pounding surf and strong winds.

Tropical Storm Erin is approaching Puerto Rico and the Virgin Islands, bringing heavy rains that could cause flooding and landslides

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