Subtropical Storm Alberto: Emergency warnings issued with torrential rain expected to batter Florida, Louisiana, Mississippi and Alabama

Flooding, high winds and massive waves all predicted as hurricane season begins

An empty beach as subtropical storm Alberto approaches Cancun, Mexico (REUTERS)

States along America’s Gulf Coast have declared emergencies as the region prepares to be battered by the season’s first subtropical storm.

Heavy downpours are expected to lash Florida, Louisiana, Mississippi and Alabama from Sunday as Storm Alberto arrives.

The National Hurricane Center, in Miami, issued weather warnings and told residents to take precautions. Waves as high as 18 feet are predicted to pound popular beaches along vast swathes of the coast including in Alabama and northwest Florida.

"Heavy rains and gusty winds continue to spread," the centre tweeted. "Hazardous storm surge is possible along portions of the central and eastern Gulf Coast beginning Sunday."

Alberto is the first named storm of the 2018 hurricane season which officially starts June 1.

It has already pounded parts of eastern Mexico and Cuba causing some localised flash flooding. It is expected to make US landmass on Monday.

The governors of Florida, Alabama and Mississippi have all declared states of emergency ahead of its arrival.

The city of New Orleans – one of the most geographically vulnerable metropolises – urged residents and businesses to be “prepared and stay informed”.

The main threat is from heavy rain that could lead to flooding, the city said, but added that high winds and storm surge could cause problems.

"I strongly encourage everyone to be safe and stay informed," Mayor LaToya Cantrell said in a statement reported by CNN.

Subtropical storms like Alberto have less defined and cooler centres than a tropical storm, which generally makes them less fearsome. However, they can quickly develop into tropical storms, which in turn can strengthen into hurricanes.