In the Gulf of Mexico, Katrina continued to gain strength as it turned northwest, then north towards southeast Louisiana and southern Mississippi. On the morning of Sunday, August 28, Katrina was upgraded to a top-notched Category 5 hurricane. Around 10 am, Mayor Nagin issued a mandatory evacuation of the entire city, the first such order ever issued in the city's history. An estimated 1 million people evacuated from Greater New Orleans and nearby areas before the storm. However, some 20% of New Orleans residents were still in the city when the storm hit. This included people who refused to leave home, those who felt their homes were adequate shelter from the storm, and people without cars or without financial means to leave. Some took refuge in the Superdome, which was designated as a "shelter of last resort" for those who could not leave.