Hurricane Erin has turned into a Category 5 storm, rapidly powering up over the course of 24 hours, the National Hurricane Center said.

While the compact hurricane’s centre was not expected to strike land, it threatened to dump flooding rains in the northeast Caribbean as it continued to grow larger.

The first Atlantic hurricane of 2025, Erin ramped up from a tropical storm to a Category 5 hurricane in a single day. By late Saturday morning, its maximum sustained winds had more than doubled to 160 mph (255 kph).

Mike Brennen, director of the National Hurricane Center in Miami, said Erin grew into a “very powerful hurricane”, with its winds gaining 60mph (96kph) in about nine hours.

The storm was expected to double or even triple in size in the coming days.

Tropical storm watches were issued for St Martin, St Barts and St Maarten and the Hurricane Center warned that heavy rain in some areas could trigger flash flooding, landslides and mudslides. The Turks and Caicos Islands southeast of the Bahamas were also under a tropical storm watch.

Powerful rip currents could affect the US East Coast from Florida to the mid-Atlantic next week, despite the eye of the storm forecast to remain far offshore, Mr Brennan said.

The Hurricane Center said Erin should begin to slowly weaken Monday as the storm encounters increased wind shear. 

Hurricane specialist and storm surge expert Michael Lowry said Erin gained strength at a pace that was “incredible for any time of year, let alone August 16th”.

Lowry said only four other Category 5 hurricanes have been recorded in the Atlantic on or before August 16.

The most powerful storms tend to form later in the year, with the hurricane season typically peaking in mid-September.