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 has restrengthened to a Category 4 storm as it turns northwest and is expected to remain east of the U.S., according to the National Hurricane Center.