5 a.m.: Katrina is upgraded to a Category 3, or major hurricane, with the Gulf Coast in its path.
During the day, residents of Louisiana's low-lying areas are told they must evacuate; residents in other low-lying areas are urgently advised to do so. President Bush declares a state of emergency in Louisiana.
Highways leading out of New Orleans are filled with bumper-to-bumper traffic. Several major interstates are converted to one-way routes away from the city.
11 p.m.: The National Hurricane Center issues a hurricane warning from Morgan City, Louisiana, to the Alabama-Florida border, an area that includes New Orleans. A warning means that hurricane conditions are expected within the warning area within the next 24 hours.