The robbery happened around 1:49 p.m. Wednesday at a U.S. Bank branch inside a Pavilions grocery store on the 3900 block of Portola Parkway in Irvine.
The suspect handed a bank clerk a note that read, "Empty Drawer, do not touch alarm. High powered gun, 15 seconds." He was wearing a black motorcycle helmet, black nylon jacket and blue jeans.
Witnesses described him as a white male, between 25 and 32 years old, about 6 feet 2 inches tall and 190 pounds.
Authorities believe the suspect has robbed at least eight other Orange County banks since December.