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 grow into a major hurricane en route to Bermuda.

The storm was over open water about 690 miles (1,110 kilometers) south-southwest of Bermuda late Wednesday, with maximum sustained winds of 80 mph (130 kph) and moving northwest at 16 mph (26 kph).

A hurricane watch was issued for Bermuda, while 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.

“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 remained up because of continuing rain.

In the north coastal town of Toa Baja, which is prone to flooding, dozens of residents moved their cars to higher areas.

“Everyone is worried,” Víctor Báez said as he sipped beer with friends and watched the rain fall. He only briefly celebrated that he had power. “It's going to go out again,” he predicted.

Ernesto, a Category 1 hurricane, was forecast to gain power in the coming days and possibly reach the strength of a major Category 3 hurricane by Friday, and its center was expected to pass near Bermuda on Saturday.

“Residents need to prepare now before conditions worsen,” Bermuda's National Security Minister Michael Weeks said. “Now is not the time for complacency.”

Forecasters also warned of heavy swells along the U.S. East Coast.

“That means that anybody who goes to the beach, even if the weather is beautiful and nice, it could be dangerous … with those rip currents,” said Robbie Berg, warning coordination meteorologist with the National Hurricane Center.

Between 4 and 6 inches of rain had been forecast for the U.S. and British Virgin Islands and 6 to 8 inches in Puerto Rico, with up to 10 inches in isolated areas.

More than 640,000 customers lost power in Puerto Rico, and 23 hospitals were operating on generators, Gov. Pedro Pierluisi said Wednesday. He added that crews were assessing damage and it was too early to tell when electricity would be restored.

“We are trying to get the system up and running as soon as we can,” said Juan Saca, president of Luma Energy, the company that operates transmission and distribution of power in Puerto Rico.

Luma Energy said earlier Wednesday that its priority was to restore power to hospitals, the island’s water and sewer company and other essential services. More than 300,000 customers were without water as a result of power outages, Pierluisi said.

Puerto Rico’s power grid was razed by Hurricane Maria in 2017 as a Category 4 storm, and it remains frail as crews continue to rebuild the system.

“It’s just frustrating that this many years later, we continue to see something like a storm cause such widespread outages in Puerto Rico, particularly given the risk that these outages can cause for vulnerable households in Puerto Rico,” said Charlotte Gossett Navarro, the Hispanic Federation’s chief director for Puerto Rico.

Not everyone can afford generators on the island of 3.2 million people with a more than 40% poverty rate.

“People already prepared themselves with candles,” said Lucía Rodríguez, a 31-year-old street vendor.

Rooftop solar systems are scarce but keep growing in Puerto Rico, where fossil fuels generate 94% of the island's electricity. At the time María hit, there were 8,000 rooftop installations, compared with more than 117,000 currently, according to the Institute for Energy Economics and Financial Analysis.

Ernesto is the fifth named storm and the third hurricane of this year’s Atlantic hurricane season. Since 1966, only four other years have had three or more hurricanes in the Atlantic by mid-August, according to Philip Klotzbach, Colorado State University hurricane researcher.

The National Oceanic and Atmospheric Administration has predicted an above-average Atlantic hurricane season this year because of record warm ocean temperatures. It forecast 17 to 25 named storms, with four to seven major hurricanes.