NEW ORLEANS, Louisiana (CNN) -- New Orleans Mayor Ray Nagin ordered a mandatory evacuation of the city beginning 8 a.m. Sunday morning but urged residents to consider escaping "the mother of all storms" before then. New Orleans residents leave Friday via Interstate 10 westbound ahead of Hurricane Gustav. 1 of 3 more photos » "You need to be scared," Nagin said. "You need to be concerned and you need to get your butts moving out of New Orleans right now. This is the storm of the century."