ST. PETERSBURG, Fla. (CBS) -- Beaches in Florida were largely empty ahead of Memorial Day as a slowly intensifying storm carrying brisk winds and heavy rain approached the U.S. 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 are banned due to high surf and dangerous conditions.
Subtropical Storm Alberto -- the first named storm of the 2018 hurricane season -- 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 (NHC) in Miami said in a statement. The governors of Florida, Alabama and Mississippi all declared states of emergency ahead of the storm.
The hurricane center said Sunday that a tropical storm warning was in effect from Bonita Beach, Florida, to the Mississippi-Alabama border.
On Sunday, gusty showers began lashing parts of Florida, and authorities were warning of the possibility of flash flooding.
The National Weather Service (NWS) said Sunday that tropical storm warnings cover the entire Florida Gulf Coast and inland portions of the Florida Panhandle as well as parts of coastal Alabama.
Isolated tornadoes were possible across the region on Sunday and Monday.
At 11a.m. EDT Sunday, the NHC said Alberto was about 130 miles southwest of Tampa, Florida, and moving north at 14 mph. The storm had top sustained winds of 50 mph.
About 5 to 10 inches of rain are possible along affected areas in eastern Louisiana, Mississippi, Alabama, western Tennessee and the western Florida Panhandle. Isolated areas could see as much as 15 inches.
Under overcast skies and occasional drizzle, several Gulfport, Mississippi, residents lined up to fill 10- and 20-pound bags with sand they will use to block any encroaching floodwater expected as a result of Alberto.
Tommy Whitlock said sandbagging has become a usual event in his life since he lives next to a creek.
"I'm doing this because every time we have a hard rain, it floods at my house," Whitlock said. "We get water from other neighborhoods, and water can get up to a foot deep in some places."
Eddy Warner, a retired consultant for a construction company, filled bags while waiting for his nephew to come help transport them home to protect his garage.
"I'm 65 years old and too old to be doing this," he said, laughing.
Alberto expected to strengthen until it reaches the northern Gulf Coast, likely on Monday night.
The NWS said waves as high as 18 feet could pound the popular Gulf beaches in Baldwin County, Alabama, and northwestern Florida on Monday.
A high surf warning was in effect through 7 p.m. Tuesday local time.
A tropical storm warning remained in effect for Cuba's western Pinar del Rio province, where heavy rains could trigger flash floods and mudslides, the NHC said.
Mexico canceled its watch for the resort-dotted coast of the Yucatan peninsula, where the storm brought heavy rain.
There were no immediate reports of emergencies. In Cancun, local newspapers showed scenes of some streets flooded to mid-hubcap level.
The downpours could dampen Memorial Day, the unofficial start of the summer tourist season along Gulf beaches.
Along with heavy rains and high winds come rough seas and a threat of rip currents from Florida to Louisiana that can sweep swimmers out to sea.
Tracey Gasper and her 6-year-old son, Chase, traveled to Biloxi Beach from Donaldsonville, Louisiana, for a day of fun in the sun with a group of friends from Baton Rouge, Louisiana.
The weather had scared off the usual crowds expected for the holiday weekend.
"It was a 50-50 chance of whether to come down and we decided to chance it," Gasper said.
What is a tropical storm watch?
A tropical storm watch means that tropical storm conditions are possible for the area and time frame described.
At the most recent information available from NOAA, the Cuban province of Pinar del Rio and areas of Mexico from Tulum to Cabo Catoche should monitor Alberto for the next 24 hours.
What is a subtropical storm?
The NHC defines subtropical storm as a "subtropical cyclone" in which the maximum sustained wind speed -- using the U.S. one-minute average -- is 39 mph or higher. Subtropical storms have cooler centers than tropical storms, but they can eventually develop into tropical storms and then into hurricanes.
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