What Are the Mechanics of a Storm Surge?

A storm surge is an offshore rise in water that is usually associated with a tropical cyclone. Storm tide is another term that may be used to refer to this rising of water level. The National Hurricane Center uses the estimated water height for the time of year, high and low tide times or astronomical tide phase as the norm when reporting a storm surge height.

Storm surges occur with low pressure weather systems and high winds. This combination makes the water higher than its normal sea level. The pressure changes in a tropical cyclone will make the ocean levels higher in areas of low pressure and cause the water levels to fall in high pressure areas. The low pressure area basically sucks the water in an upward direction.

The combination of constant wind and a low pressure area over shallow water is the most frequent cause of flooding. Hurricane Katrina caused massive devastation along the Gulf Coast of the United States with its storm surge. Low lying coastal areas are more susceptible to storm surges from hurricanes and the Gulf Coast is very prone to them. The damage from storm surges will also be greater at a high tide time than if they occur during a low tide.

Hurricanes or other coastal storms push the storm surge water to shore with the force of the wind. The eye of the storm will pile up water in a dome shape. If the dome shape forms far offshore it will eventually sink and cause no damage. If the dome hits a shoreline it can send a water wall up to twenty five feet deep many miles across the shoreline. To further understand the potential for damage, water weighs one metric ton per cubic meter. This is an enormous amount of force hitting a shoreline.

In the Northern Hemisphere the most damaging area of a storm surge is in the right front quadrant. This is due to the counter-clockwise rotation of the winds and ocean wave movement. On the left side of the storm eye the winds will blow in an offshore direction which will moderate some of the surge.

With advance storm warnings and evacuations lives can be saved but property protection requires work. Natural buffers are frequently destroyed by coastal developments. Coral reefs, coastal vegetation and barrier islands all protect the coastal area from some of the damages caused during a storm surge. Rebuilding and restoring these natural areas is one way to protect coastlines from damage.

References:

http://ast.ednet.ns.ca/journal/journal2003/ss.pdf

http://www.nhc.noaa.gov/HAW2/english/storm_surge.shtml

http://www.magazine.noaa.gov/stories/mag178.htm