Storm Surge

What is Storm Surge?

When a hurricane makes landfall, the biggest danger isn’t from the rain or the wind. It’s the flooding caused by storm surge.

A hurricane’s spiralling winds create a centrical force that makes a dome of water at the center of the storm. In the ocean this mound of water eventually sinks without causing harm. It becomes a danger when the hurricane reaches land and the water piles up to cause coastal flooding. When this happens during high tide, storm surge can be even more devastating. This double whammy is called storm tide. It has been responsible for huge floods.

 A hurricane can cause sea level to rise as much as 20 or 30 feet higher than normal. The sea level rise only lasts a short time, usually just a few hours, but it can cause a huge amount of damage. The rising water may totally submerge low-lying areas and towns along the coast. Huge ocean waves cause damage too, demolishing docks, houses, roads, and eroding beaches.
A storm surge hammers a shorelineUsually the stronger the winds the more powerful the hurricane is and the higher the storm surge. The winds create low pressure creating a vacuum to raise sea level and make dramatically higher waves. Wind direction towards shore  pushes water inland. When the wind follows along the coast water is pushed along the shore.

A storm surge can obliterate every object in its way. Trees, buildings, boats and cars can be demolished. One of the highest recorded storm surges was Hurricane Camille in 1969. A 25 foot (7.6 m) surge crashed into Pass Christian, Mississippi. It killed thirty people who had gone to an ocean-front apartment to attend  a “hurricane party”.

In the US  storm surge is not the biggest cause of death from hurricane activity. Only 1% of hurricane-related deaths in the US are from storm surge. Most hurricane-related deaths in the US are from inland flashfloods. In other countries though, almost all hurricane-related deaths are because of storm surges. Storm surges have killed hundreds of thousands of people in   Bangladesh alone.Lower elevations allow water to be pushed further inland.

How much storm surge will a hurricane produce? Forecasters use computer modelling to calculate potential storm surge. SLOSH is such a model that looks at a storm’s path and strength and combines it with data on ocean depths and the shape of land where the storm may make landfall to predict how much storm surge to expect.

Storm surge risk maps can be prepared by mapping low-elevation areas along the shoreline. Areas of highest storm surge inundation risk are low elevation areas along the coast and inland water routes. Lower risk areas are at higher elevations and/or farther inland.