Hurricane Katrina began as a very low pressure weather system, which strengthened to become a tropical storm and eventually a hurricane as it moved west and neared the Florida coast on the evening of 25 August.
Animated guide: How Hurricanes form
After crossing southern Florida - where it left some 100,000 homes without power - it strengthened further before veering inland towards Louisiana, eventually making landfall at Grand Isle, approximately 90km south of New Orleans, at 10am local time on 29 August.
At this point, Katrina's sustained wind speed was approximately 200 km/h.
The storm passed directly through New Orleans, destroying many lighter buildings and causing extensive damage to others.
Hurricane force winds were recorded along a 200km stretch of coastline, with scenes of similar destruction and flooding in Louisiana, Mississippi and Alabama. Storm surges from the sea caused flooding several kilometres inland in some places.