(CNN) Subtropical Storm Alberto was disrupting plans for Memorial Day barbecues and beach outings in Alabama, Florida and Mississippi, as the storm continued churning north through the Gulf of Mexico on Sunday.

Alberto is scheduled to make landfall on the Florida Panhandle early Monday, and the three states likely to bear the brunt of the storm have begun preparing states of emergency.

Florida Gov. Rick Scott issued the declaration for all 67 counties in his state. Mississippi Gov. Phil Bryant authorized the use of the National Guard, his office said in a statement.

Alabama Gov. Kay Ivey issued a state of emergency for 40 counties, starting at 6 a.m. Sunday. Ivey activated the state's emergency operations center while the Alabama National Guard activated its high water evacuation teams.

Alberto is expected to produce heavy rainfall and flooding over western Cuba, South Florida and the Florida Keys, the National Hurricane Center said Sunday.

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