Residents of southern Florida have been warned not to travel as a “life-threatening” storm moves across the state.

The storm was about 145 miles east-northeast of Fort Pierce, moving at a speed of about 20mph, late on Saturday.

It is forecast to bring rainfall of up to 10 inches (25cm) in south Florida, including the Florida Keys, and has already caused three deaths and property damage in Cuba.

The city of Miami tweeted: “This is a dangerous and life-threatening situation.

“Travelling during these conditions is not recommended.

“It is better to wait – turn around, don’t drown.”

The National Hurricane Center said that the storm – known as Agatha in the Pacific Ocean – will be named Alex in the Atlantic Ocean basin if it is designated as a tropical storm.

Maximum sustained winds are currently near 45mph, with the storm expected to strengthen into Monday as it moves into the Atlantic.

A storm is categorised as a tropical storm if its winds are between 39 and 72 mph.

The threat of flash flooding was expected to diminish on Sunday, although the threat of urban flooding was increased, the centre said.

A tropical storm watch is in effect for Bermuda, which is already experiencing flooding and strong winds.

Miami Beach mayor Dan Gelber said drainage pumps in his area had been tested by the storm, adding: “We moved the water off pretty quickly, but in some areas, obviously, it was really challenging.

“There were some problems getting through on some streets, one of the main arteries was unpassable, but by and large water is dissipating.”