Officers discovered Enrique Jimenez suffering from gunshot wounds in a vehicle in the parking lot of the Grocery Outlet at 66 Admiral Callaghan Lane at around 5 a.m.
Jiminez died at the scene, police said.
Witnesses described a suspect who fled on foot toward Henry Street as a Hispanic man, 5 feet 5 inches tall and 160 pounds.
Police are asking additional witnesses to come forward to help provide an account of the events leading up to the shooting.
Anyone with information is asked to call police at (707) 651-7146 or the anonymous tip line at (800) 488-9383.