Damage to buildings near Norman is being assessed Sunday. Several businesses were damaged by an apparent tornado that struck near Interstate 35 and State Highway 9 on Saturday night. [Photo by Steve Sisney, The Oklahoman]

NORMAN — A tornado hit Riverwind Casino on Saturday night while the Beach Boys performed before a sold-out crowd inside.

"There's somebody still out in the field investigating all the activity last night. Right now, there appears to be only one tornado in the Norman area," National Weather Service meteorologist Daryl Williams said Sunday evening.

The tornado's strength has not been categorized yet, but more information is expected Monday, Williams said.

Preliminary reports show that the tornado was both weak and short-lived, Williams said.