SAN JUAN, Puerto Rico — Hurricane Ernesto barrelled toward Bermuda on Thursday after leaving hundreds of thousands of people in Puerto Rico without power or water as sweltering heat enveloped the U.S. territory, raising concerns about people’s health.

A hurricane warning was in effect for Bermuda, with Ernesto expected to pass near or over the island on Saturday.

The Category 1 storm was located about 605 miles (975 kilometers) south-southwest of Bermuda on Thursday morning. It had maximum sustained winds of 85 mph (140 kph) and was moving north at 13 mph (20 kph).

“I cannot stress enough how important it is for every resident to use this time to prepare. We have seen in the past the devastating effects of complacency,” said National Security Minister Michael Weeks.

Ernesto was forecast to become a major Category 3 hurricane on Friday and then decrease in strength as it approaches Bermuda, where it is expected to drop between four to eight inches of rain, with up to 12 inches in isolated areas.

“All of the guidance show this system as a large hurricane near Bermuda,” said the National Hurricane Center in Miami.

Meanwhile, the spinning storm on Thursday was generating southern winds in Puerto Rico, which have a heating effect as opposed to the typical cooling trade winds that blow from the east.

“We know a lot of people don’t have power,” said Ernesto Morales with the National Weather Service as he warned of extreme heat and urged people to stay hydrated.

Nearly half a million of 1.4 million customers remained in the dark more than a day after Ernesto swiped past Puerto Rico late Tuesday as a tropical storm before strengthening into a hurricane.

Hundreds of thousands of people also are without water given the power outages.

The situation worried many who lived through Hurricane Maria, a powerful Category 4 storm that hit Puerto Rico in September 2017 and was blamed for at least 2,975 deaths in its sweltering aftermath.

The National Weather Service issued a heat advisory on Thursday warning of “dangerously hot and humid conditions.”

Officials said they don’t know when power would be fully restored as concerns grow about the health of many in Puerto Rico who cannot afford generators or solar panels on the island of 3.2 million people with a more than 40% poverty rate.

Crews were still assessing the situation, although no catastrophic damage has been identified, said Juan Saca, president of Luma Energy, a private company that operates the transmission and distribution of power in Puerto Rico.

When pressed for an estimate of when power would be restored, Alejandro González, Luma’s operations director, declined to say.

“It would be irresponsible to provide an exact date,” he said at a news conference late Wednesday.