Hurricane Ernesto dropped torrential rain on Puerto Rico and knocked out power for nearly half of all customers in the U.S. territory Wednesday as it threatened to strengthen into a major hurricane en route to Bermuda.

The storm was over open water about 635 miles south-southwest of Bermuda early Thursday, with maximum sustained winds of 85 mph and moving north at 13 mph. A hurricane watch was issued for Bermuda, where tropical storm conditions were possible Friday and hurricane conditions were possible Saturday. Tropical storm warnings were discontinued for Puerto Rico and its outlying islands of Vieques and Culebra and for the U.

S. and British Virgin Islands after the storm passed. “I know it was a long night listening to that wind howl,” U.

S. Virgin Islands Gov. Albert Bryan Jr.

said at a news conference. An islandwide blackout was reported on St. Croix, and at least six cellphone towers were offline across the U.

S. territory, said Daryl Jaschen, emergency management director. Schools and government agencies were closed in the U.

S. and British Virgin Islands and Puerto Rico, where heavy flooding was reported in several areas, forcing officials to block roads, some of which were strewn with trees. More than 140 flights were canceled to and from Puerto Rico.

“A lot of rain, a lot of rain,” Culebra Mayor Edilberto Romero said in a phone interview. “We have trees that have fallen on public roads. There are some roofs that are blown off.

” Flash flood warnings remain.