Hurricane Ernesto is heading for the Caribbean island of Bermuda, having crossed Puerto Rico where it left more than half of homes and businesses without power.
With wind gusts of 100mph (155km/h), Ernesto has now strengthened to a category-two hurricane, the US National Hurricane Center (NHC) says in its latest bulletin at 03:00 GMT on Friday.
It warns that Ernesto “could be near major hurricane strength on Friday”, and is expected to pass near or over Bermuda on Saturday.
A dangerous storm surge with “large and destructive waves” and significant coastal flooding are expected, the NHC adds.
Bermuda is a British territory made up of 181 islands in the Atlantic ocean.
Forecasters have previously warned of the role of climate change in making storms like this one more intense.
Ernesto swept past Puerto Rico on Thursday night, the NHC said.
Puerto Rico’s main power supplier Luma Energy was reporting that some 410,000 customers did not have access to electricity by around midday Thursday, according to Reuters news agency.
Juan Saca, Luma’s president and chief executive, said more than 1,500 employees were working in the field to “re-establish service” and switch the electricity back on.
“We have to evaluate what needs to be done to be able to resolve it,” he said.
Puerto Rico’s power grid has been wiped out before by hurricanes. In 2022, when Hurricane Fiona hit the island, around 80% of homes and businesses were cut off for almost a month.
Ernesto is the fifth named Atlantic storm to occur this season.
Hurricane Beryl was the earliest category-five storm on record in the Atlantic when it swept through the Caribbean and the Texas Gulf Coast last month, killing dozens of people and leaving millions without electricity.
Earlier this year, US weather agency Noaa warned that the North Atlantic could get as many as seven major hurricanes of category-three strength or over this year, which would be more than double the usual number.
While there is no evidence climate change is producing more hurricanes, it is making the most powerful ones more likely, and bringing heavier rainfall.
