ST. PETERSBURG, Fla. — Beaches in Florida were largely empty ahead of Memorial Day as a slowly intensifying storm carrying brisk winds and heavy rain approached the Gulf Coast on Sunday.

The storm disrupted plans from Pensacola in the Panhandle to Miami Beach on Florida’s southeastern edge.

Lifeguards posted red flags along the white sands of Pensacola Beach, where swimming and wading were banned because of high surf and dangerous conditions.

Subtropical Storm Alberto – the first named storm of the 2018 hurricane season that starts June 1 – prompted Florida, Alabama and Mississippi to launch emergency preparations Saturday. Rough conditions were expected to roil the seas off the eastern and northern Gulf Coast region through Tuesday.

“These swells are likely to cause life-threatening surf and rip current conditions,” the National Hurricane Center in Miami said.

In Miami, organizers called off the sea portion of the Miami Beach Air & Sea Show on Sunday because of heavy rain and rough waters. And in the Tampa Bay area on the central Gulf Coast, cities offered sandbags for homeowners worried about floods.

Live video from webcams posted in Clearwater and Destin showed half-empty beaches, and whitecaps roiled the normally placid Gulf.

Gusty showers were to begin lashing parts of Florida on Sunday, and authorities were warning of the possibility of flash flooding.

The hurricane center said Sunday that a tropical storm warning was in effect from Bonita Beach, Florida, to the Mississippi-Alabama border.