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.

Erin is now a Category 3 hurricane with outer rainbands producing gusty winds and heavy rains across the Virgin Islands, Puerto Rico and the Dominican Republic.