4 a.m.: Hurricane Katrina is downgraded to a strong Category 4 storm.
7 a.m.: Katrina makes landfall on the Louisiana coast between Grand Isle and the mouth of the Mississippi River.
11a.m. Katrina makes another landfall near the Louisiana-Mississippi state line with 125 mph winds. The storm's daylong rampage claims lives and ravages property in Louisiana, Mississippi and Alabama, where coastal areas remained under several feet of water. (Gallery)
Two major flood-control levees are breached, and the National Weather Service reports "total structural failure" in parts of New Orleans. A section of the roof of the Louisiana Superdome, where 10,000 people are taking refuge, opens. (Full story) Many are feared dead in flooded neighborhoods still under as much as 20 feet of water.
In Mississippi, dozens are dead and Gov. Haley Barbour describes "catastrophic damage" along the coast. More than 1.3 million homes and businesses in Louisiana, Mississippi and Alabama were without electricity, according to utility companies. (Full story)
10 p.m.: More than 12 hours after making landfall, one of the most powerful hurricanes to hit the northern Gulf Coast in half a century is downgraded to a tropical storm. Remnants head north toward Tennessee and the Ohio River Valley, spurring harsh storms and tornadoes.