Tropical Storm Bonnie -- downgraded Sunday to a tropical depression -- made landfall in the southern state of South Carolina, putting a damper on holiday weekend plans for millions of Americans.

At 11 am (1500 GMT), Bonnie was about 30 miles (50 kilometers) northeast of Charleston, South Carolina, with maximum sustained winds of 35 miles (55 kilometers) per hour, according to the latest bulletin from the Miami-based National Hurricane Center.

Bonnie was expected to weaken further as it moves inland, but heavy rains were expected in areas it passes over.

The storm hit land in the middle of the three-day Memorial Day weekend. The public holiday observed on Monday commemorates fallen service members.

The holiday -- considered the unofficial start of summer -- finds many Americans heading to parks and beaches for barbecues, picnics and parades in towns and cities across the nation.

On Friday, US weather forecasters issued their prediction for the Atlantic hurricane season that begins June 1 and runs through November 30, saying it would be "near normal," although with more storms than in recent years.

The Atlantic will likely see between 10 and 16 tropical storms, of which four to eight could become hurricanes, said the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center.