Hurricane Erin weakened to a Category 3 hurricane on Sunday, its outer bands lashing the Virgin Islands and Puerto Rico, as forecasters warned the storm was rapidly growing in size and would gain new strength.

The rain and winds from the outer bands of the storm left about 147,000 customers without power Sunday morning in Puerto Rico, according to Luma Energy, a private company that oversees the transmission and distribution of power on the island. The weather canceled more than 20 flights, officials said.