Storm Surge

While a hurricane is out over the open ocean, there is not any storm surge to speak of. There is what is called an inverted barometer effect where the ocean level is slightly higher in the center of the hurricane due to the lowered atmospheric pressure. However, this effect is so small that it does not make a large difference once the hurricane makes landfall.

When the center of a hurricane (or even a tropical storm) approaches the coastline, the winds really pick up and act to push the ocean onto the coastline. The diagram to the right illustrates how a hurricane that is moving onshore will pile up the ocean just ahead of the center or eye.

Angle of Attack/Right-Front Quadrant
Angle of attack is a very important aspect to consider when determining the potential damage from a hurricane storm surge. Remember that the right-front quadrant (RFQ) is the stronger side of the storm and will deliver the highest storm surge. A powerful hurricane can be roaring up the coast at a good 20 mph and pass us by to the east by only 20 or 30 miles. Yes, we will have hurricane force winds and heavy rains but we would be spared the destructive RFQ and the storm surge that accompanies it.

A hurricane striking the coast head on, or perpendicular, will do the most damage as far as storm surge is concerned. South facing beaches that are struck by a north moving hurricane would fit this profile. Also, east facing beaches that are struck by a westward moving hurricane would receive a perpendicular strike. Let's now look at a hurricane that parallels the coast:

The Result
The illustrations below depict a category two hurricane and a category four hurricane at the beachfront. The illustrations show the beach in profile to demonstrate scale. Notice the differences in the two scenarios. The category two hurricane causes dune erosion and minor ocean overwash on well nourished barrier islands. Thus the damage is typically minor as compared to what will likely occur during a category four hurricane.

The Inland Danger
Storm surge is usually considered the most dangerous part of a hurricane. Recently though, inland flooding has been the big killer. It has been responsible for more than half of hurricane-related deaths. One quarter of those deaths from 1970-1999 were people who drowned in their cars.

Two feet of water can float a car. Hurricanes can dump five to 10 inches of rain and, in some cases, more than 20 inches of rain can fall. Local residents were assaulted with more than 30 inches of rain from Hurricane Danny in 1997; 24 inches drenched the area in 1998 from Hurricane Georges. In these situations, storm drains can’t handle all the water and may become clogged with debris. Rivers will rise out of their bank and many areas will flood quickly. For more information, see our Floods page..