When a hurricane approaches the shoreline, the winds on the right hand side of the hurricane (looking toward where the hurricane is moving) push the ocean water ahead of it. The ocean can rise to great levels. During the Category 3 Hurricane Camille the storm tide was 24.6 feet (7.5 meters), but during the even more destructive Category 3 Hurricane Katrina, the storm surge was over 28 feet (8.5 meters) above the normal tide. How a storm works is seen below. In the example, a 15 foot storm surge is added to the normal 2 foot High Tide giving a 17 foot Storm Tide.
Although, winds, flooding and occasional tornadoes accompany hurricanes, most damage and death are caused by the storm surge. The surge consists of the rising of the sea level caused by low pressure, high winds, and high waves. These are characteristic of hurricanes as they reach land. Storm surges cause significant flooding, and being caught in one is extremely hazardous.
The fall in air pressure with a hurricane helps with the
rise in water. Normal pressure at sea level is 29.92126 inches or 14.6969
pounds per square inch. In the wall of the hurricane's eye, ascending
and spiraling winds lift over a million tons of air per second. This process
drops the surface pressure as the air soars. The surface of the sea rises
one foot for each one inch drop in barometric pressure due to the air
rising within the eyewall.
Although Camille was a Category 5 hurricane and Katrina a category 3 hurricane when they made land fall, the damage caused by Katrina was much more extensive than that caused by Camille. What might be an explanation?
If you think about the weight or mass of water, it is easy to understand why a storm surge can cause so much damage. One cubic meter of water has a mass of 1,000 kilograms. If we look at the weight of water using the British system, most of us are used to, we see that a cubic yard of water weighs nearly 1,700 pounds! From this, it is easy to see why a storm surge causes so much damage.
An example of the damage caused by Hurricane Katrina's storm surge.
Additional Information:
NOAA Hurricane Education on storm surge (will download as a Word .doc file)
Hurricane Damage at Think Quest
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