How Hurricanes cause Storm Surges

Hurricanes and tropical storms are the primary causes of storm surges. In order to understand such a concept, a storm surge must be defined.

A storm surge is an abnormal rise in water levels caused by heavy winds. The water levels, particularly in the oceans, have risen above the average astronomical tide height. Put simply, a storm surge is a difference between calm and rough water levels, and no reference in and of itself is used. For example, if you go boating out on a lake and a thunderstorm is working its way toward that lake, the winds will increase and push that water level higher than it would be on a calm, sunny day. The water level is raised due to the oncoming winds.

However, when the rising tide is combined with a storm surge, such as at mean sea level, a reference point is used. Let’s suppose a storm surge of 12 feet is combined with a tide that is 3 feet higher than normal. In this instance, you will have a storm tide of 15 feet! In regard to storm surges, they can penetrate quite a ways inland from the affected coastline. If a hurricane is powerful enough, the surge can go as far as 30 miles or even more. The US east coast and the islands in the Carribean are particularly vulnerable to storm surge because this is where most hurricanes occur.

When wind circulates around the eye of a hurricane, it affects the ocean’s surface vertically in deep water, but at this point, there is very little indication of storm surge. However, once that hurricane reaches shallower water levels, the vertical circulation is disrupted by the ocean floor. When that happens, the water has no place to go but upward and inland. This is then known as storm surge. Typically, this takes place where winds are blowing onshore. Thus, the highest surges will occur at the location of the strongest winds.

As for the devastaing damage caused by high category hurricanes, it takes place due to a combination of such surges, the tides, which are naturally-occurring fluctuations caused by the combined gravitational pull of the moon and sun, and the waves in the ocean itself. Therefore, when you see major flooding on the news following a hurricane that has come inland in one of these aforementioned geographical areas, this is the result of storm surge, tides, and waves combined. Two of the most catastrophic storms in recent history were Hurricane Katrina and Hurricane Ike. Katrina produced a 28 ft storm surge while Ike produced one of 20 ft.

The floods brought on by storm surges are often more dangerous than the high wind speed of the hurricane itself. Hurricanes actually weaken by a considerable margin once they move inland. The problem is that the storm surges result not only in sea water expanding inward to inhabited areas, but also torrential rainfall. As a result, it’s not uncommon to see as much as 6-12 inches of rainfall over a short period of time. Flooding causes extensive damage to property and loss of life. While any hurricane wind around 75 miles per hour is capable of rendering structural damage and can even produce secondary tornadoes, it should be stressed that the ensuing flooding from storm surges can be just as if not more catasrophic.

If you live in an area that is susceptible to hurricanes or tropical storms and one happens to be headed your way, it is prudent to follow the advice of authorities that know what such storms are capable of doing.