SAN JUAN, Puerto Rico >> Tropical Storm Ernesto strengthened into a Category 1 hurricane today as it churned away from the Virgin Islands and Puerto Rico, leaving more torrential rains in its wake and cutting power to hundreds of thousands of homes and businesses.

Ernesto was about 175 miles northwest of the Puerto Rican capital of San Juan as it crawled to the northwest, packing winds of about 75 miles per hour, the National Hurricane Center said in an advisory today.

“The official forecast still reflects the possibility of Ernesto becoming a major hurricane in about 48 hours,” the center said.

A storm is considered a hurricane when its sustained winds reach 74 mph. A major hurricane — a Category 3 or higher — has a sustained wind speed of at least 111 mph.

Ernesto — the fifth named Atlantic storm of the season — should approach the British island territory of Bermuda, about 665 miles east of North Carolina, by Saturday, with rainfall beginning as early as Thursday, the NHC said.

More than 500,000 homes and businesses were without power early today in Puerto Rico, according to LUMA Energy, which provides electricity to the U.S. island territory.

“We will conduct field inspections as soon as it is safe for our crews to go out into the field to identify damage and begin repairs,” LUMA said in a statement. The company said it would prioritize restoring power to essential services such as hospitals and water and sewage facilities.

More flood-producing rains were falling on the U.S. Virgin Islands and Puerto Rico, the hurricane center said, warning that floodwaters were covering some streets and causing mudslides.

“I urge you to stay safe in your homes, have the emergency numbers at hand and follow the recommendations of the official authorities. The safety of everyone is a priority,” Puerto Rico Governor Pedro Pierluisi said on X.

Puerto Rico and Virgin Island schools were closed today, as were many governmental offices. Airports on the Virgin Islands, to the east and southeast of Puerto Rico, were expected to reopen at 10 a.m. local time (1400 GMT) today.

The Virgin Islands was expected to get up to 6 inches (15.2 cm) of rain while up to 10 inches (25.4 cm) of rain was in the forecast for southeastern Puerto Rico. The Virgin Islands, Puerto Rico, Vieques and Culebra were under a tropical storm warning, the hurricane center said. Ernesto is the second named Atlantic storm in a week during this year’s intense hurricane season. Slow-moving Debby hit Florida’s Gulf Coast as a Category 1 hurricane last week before soaking some parts of the Carolinas with up to 2 feet (0.6 meter) of rain.

Hurricane Beryl, the first of the season, was the earliest recorded Category 5 hurricane on record in the Atlantic when it swept through the Caribbean and the U.S. Gulf Coast last month, killing dozens of people and costing an estimated $6 billion in damages.

Additional reporting by Brendan O’Brien.