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Hurricane Katrina - Impacts |
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In August 2005, Hurricane Katrina tore through many areas of the Gulf Coast. BBC Weather looks at how Katrina made an impact to these areas in southern USA. |
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The three main threats from a hurricane are the rain, wind and the storm surge. Under the low pressure centre of a cyclone the sea surface bulges upwards, and combined with the push from the cyclone's winds the storm surge is created. This rush of seawater swamps unprotected low-lying coastal areas, and is responsible for most loss of life from all tropical cyclones worldwide. ...Louisiana, Mississippi and Alabama all saw significant damage and loss of life. The Gulf Coast saw the biggest impact from Katrina. The states of Louisiana, Mississippi and Alabama all saw significant damage and loss of life. The storm surge from Mobile Bay flooded Mobile in Alabama, and large portions of the coastal Mississippi cities of Biloxi and Gulfport were left underwater as a result of the 6-9 metre (20-30 foot) storm surge.
New Orleans initially seemed to have escaped the worst of the winds as Katrina's eye passed to the east of the city, but the earthen levees which separate the city from the surrounding lakes could not withstand the prolonged battering from the strong winds, heavy rain and 8.5 metre (28 foot) storm surge. ...80% of the city was left under water by 31st August...
As a result 80% of the city was left under water by 31st August, after the levees were breached in several places and water flooded in from Lake Pontchartrain, which had been swollen by water surging in from the Gulf of Mexico. New Orleans sits mostly below sea level on swampland, and parts of the city were left under as much as 6 m (20 foot) of water. The levee system was built to withstand a Category 3 hurricane.
The first bands of rain associated with Katrina started affecting the coast long before landfall, and as the hurricane came ashore rainfall rates of 25 mm (1 inch) per hour were recorded along the Gulf Coast, in some spots for as long as three consecutive hours. Rainfall totals exceeded 200-250 mm (8-10 inches) along and to the east of much of Katrina's path. Wind speeds over 140 mph (224 km/h) were recorded at landfall in southeast Louisiana, and just to the left of the eye (where winds are less stronger than to the right) winds gusted over 100 mph (160 km/h) in New Orleans. 1.7 million people lost electricity across the Gulf states. At its second landfall near the Louisiana-Mississippi border steady winds were recorded as 125 mph (200 km/h), and gusts of over 90 mph (144 km/h) were recorded in Biloxi, and 80mph (128 km/h) in Mobile. 1.7 million people lost electricity across the Gulf states.
The main impact on southern Florida as Katrina passed over four days earlier was from the amount of rainfall. Some spots saw 380 mm (15 inches) of rain, which led to localised flooding. Wind speeds reached 80 mph (128 km/h) which caused some damage and power cuts to around 1.3 million people. Katrina also spawned tornadoes which caused damage...
After Katrina moved inland from the Gulf Coast the wind speeds lessened quickly and rainfall became the main threat. Up to 100 mm (4 inches) was recorded from Katrina in a large area from the Gulf Coast to the Ohio Valley, causing flood watches and warnings to be issued widely. Katrina also spawned tornadoes which caused damage in other states including Georgia.
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