Hurricane Katrina approaching the shore at Gulfport, Mississippi, USA, on 28th August 2005. Less than twelve hours after this, its record storm surge and high winds devastated the region. A storm surge is a rise in sea level caused by high winds driving waves forward in the path of the hurricane. The storm surge of almost ten meters that hit the Gulf of Mexico coast on 29th August was the largest ever recorded in the USA. Katrina was the most deadly and costly natural disaster to befall the USA. The entire population of New Orleans was evacuated after 80% of the city was flooded, killing thousands.