A storm surge is a series of high waves of water caused by wind and low pressure, most commonly associated with hurricanes.
Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level to heights that impact roads, homes and other critical infrastructure. In addition, wind driven waves often combine with the storm tide. The resulting rise in water level can cause severe flooding in coastal areas, particularly when the storm tide occurs at the same time as the normal high tide. Many buildings withstand hurricane force winds until their foundations, undermined by erosion, are weakened and fail.
Surge and wave heights on shore are affected by the configuration and bathymetry of the ocean bottom. A narrow shelf, or one that has a steep drop from the shoreline and subsequently produces deep water in close proximity to the shoreline tends to produce a lower surge, but a higher and more powerful wave. This situation is seen along the southeast coast of Florida. The edge of the Floridian Plateau, where the water depths reach 91 meters, lies just 3,000 m offshore of Palm Beach, Florida; just 7,000 meters offshore, the depth plunges to over 180 meters. Conversely, coastlines such as those along the Gulf of Mexico coast from Texas to Florida have long, gently sloping shelves and shallow water depths. On the Gulf side of Florida, the edge of the Floridian Plateau lies more than 160 km. These areas are subject to higher storm surges, but smaller waves. This difference is because in deeper water, a surge can be dispersed down and away from the hurricane. However, upon entering a shallow, gently sloping shelf, the surge cannot be dispersed away, but is driven ashore by the wind stresses of the hurricane.
In the United States and many other countries, the storm surge is not the primary cause of death associated with hurricanes. In fact, in the past twenty years, just over 1% of hurricane-related deaths in the United States have been caused by a storm surge. The majority of hurricane deaths in the United States come from inland flooding. In other parts of the world, however, virtually all hurricane-related deaths are a result of storm surges. Bangladesh is the area in the world most affected by the storm surge, with over a hundred on record. These storm surges are responsible for hundreds of thousands of deaths in the Bangladesh area alone.
One of the greatest recorded storm surges was generated by 2005's Hurricane Katrina, which produced a maximum storm surge of 25 feet around St. Louis Bay, Mississippi and Pass Christian, with a storm surge height of 27.8 feet. Another record storm surge occurred in this same area from Hurricane Camille in August 1969, with the highest storm tide of 24.6 feet.