Erin was a Category 3 hurricane Sunday, the National Hurricane Center said in its 2 p.m. ET update, with sustained winds of 125 mph, with tropical storm-force winds reaching out 205 miles. The storm is expected to continue to fluctuate in intensity,

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

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.

Hurricane Erin, after strengthening into a Category 5 storm early Saturday, weakened to Category 3 by Sunday morning and has taken a track slightly more south than originally forecast, the National Hurricane Center said.

Even when they don't brush the coast or make landfall, such storms can be deadly and cause millions of dollars of damage. Erin is expected to remain hundreds of miles offshore, according to the National Hurricane Center,