Sunday marks the 16th anniversary of Hurricane Katrina’s landfall in Louisiana as a Category 3 storm. It also marks the expected landfall of Hurricane Ida, which is forecast to crash ashore south of New Orleans at Category 4 strength, unleashing destructive 140 mph winds, flooding rain, and an ocean surge up to 15 feet.

On Friday night, the National Hurricane Center warned of “life-threatening inundation” due to the surge and “potentially catastrophic wind damage” near where Ida comes ashore, as it boosted the storm’s predicted landfall intensity a category, from 3 to 4.

New Orleans was placed under a hurricane warning, which stretches from Louisiana’s central coast to the border with Mississippi. Storm surge warnings, for the rise in ocean water above normally dry land, stretch from the Louisiana’s central coast to the Mississippi-Alabama border.

Anticipating flooding, New Orleans Mayor LaToy Cantrell issued a mandatory evacuation order for residents outside the city’s levee system Friday and called for voluntary evacuations elsewhere in the city.

“If you have any medical needs or wish to voluntarily evacuate on your own, now is the time to start that voluntary evacuation,” Cantrell said at a Friday morning news conference.