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.

As of 5 a.m. on Sunday, Hurricane Erin has weakened back to a Category 3 storm but has grown larger, the National Hurricane Center said.

A Royal Caribbean Vision of the Seas cruise from Baltimore to Bermuda will now head to Florida in order to avoid Tropical Storm Erin.