What is Storm Surge?

Rough seas breaking over the lighthouse on Roker Pier
Roger Coulam / Getty Images

A storm surge is an abnormal rise of seawater that occurs when water is pushed inland as a result of high winds from a storm, usually tropical cyclones (hurricanes, typhoons, and cyclones). This abnormal rise in seawater level is measured as the height of water above the normal predicted astronomical tide and can reach tens of feet high! 

Coastlines, especially those at low sea-levels, are particularly vulnerable to storm surge because they sit closest to the ocean and receive the highest storm surge waves.

But inland areas are at risk too. Depending on how strong the storm is, the surge can extend as much as 30 miles inland.

Storm Surge vs. High Tide

The storm surge resulting from a hurricane is one of the more deadly portions of a storm. Think of a storm surge as a giant bulge of water. Much like waves of water slosh back and forth in a bathtub, seawater also ebbs and flows back and forth in the ocean. Normal water levels rise and fall in periodic and predictable ways due to the gravitational pull between the Earth, sun, and moon. We call these tides. However, the low pressure of a hurricane combined with high winds causes the normal water levels to rise. Even high and low tide waters can rise beyond their normal levels.

Storm Tide

We've looked at how a storm surge differs from an ocean high tide. But what if a storm surge ever occurred at high tide? When this happens, the result is what's called a "storm tide." 

Storm Surge Destructive Power

One of the most obvious ways storm surge damages property and lives is by overtaking . Waves can ashore, overcoming. Waves not only move fast, but weigh a lot. Think of the last time you carried a gallon or pack of bottled water and how heavy it was. Now consider that these waves repeatedly pount and batter buildings and you can understand how surge waves  .

 

For these reasons, storm surge is also the leading cause of hurricane-related deaths. 

The force behind storm surge waves not only but also makes it possible for waves to extend inland.

Storm surge waves also erode sand dunes and roadways by washing away the sands and ground underneath them. This erosion can also lead to damaged building foundations, which in turn, weakens the entire structure itself.  

Unfortunately, a hurricane's rating on the Saffir-Simpson Hurricane Wind scale tells you nothing about how strong a storm surge to expect. That's because varies. If you want an idea of how high waves could climb, you'll need to check NOAA's Storm Surge Flooding Map

Why are Some Areas More Prone to Storm Surge Damages?

Depending on the geography of the coast, some areas are more susceptible to storm surge damages. For example, if a continental shelf is gently sloping, the power of a storm surge can be greater. A steep continental shelf will cause the storm surge to be less intense. In addition, low lying coastal areas are often at risk of increased flood damage.

Some areas also act as a sort of funnel through which water can surge even higher. The Bay of Bengal is one location where water is literally funneled into the coast.

In 1970, a storm surge killed at least 500,000 people in the Bhola cyclone.

In 2008, the shallow continental shelf in Myanmar caused Cyclone Nargis to produce intense storm surges killing tens of thousands of people. (Go to a video explaining the Myanmar storm surge.)

The Bay of Fundy, while not usually hit by hurricanes, experiences tidal bores daily due to its funnel shaped land structure. While not caused by a storm, a tidal bore is an increased surge of water from tides due to the geography of an area. The 1938 Long Island Express hurricane caused extensive damage as it hit New England and threatened the Bay of Fundy. But by far, the greatest damage was done by the Saxby Gale hurricane of 1869.

Updated by Tiffany Means