Storm surge is the water that is pushed toward the shore by the force of the winds swirling around the storm. When the center of a tropical cyclone approaches the coastline, the wind quickly picks up as the center approaches and acts to push the ocean onto the coastline. The water piles up on the shallow bank and surges towards the shore, causing massive destruction and erosion. This surge of water combines with the power of the winds and the normal tides to increase the height of the water 15 feet or more. In addition to the increase of height of the water, the winds produce powerful waves, which crush many things in its path. The result is severe flood damage along with wave damage and is most definitely the costliest and deadliest part of a hurricane.
The strength and level of a storm surge strongly depends on the height of the continental shelf at sea. If the shelf is very shallow and high compared to the ocean floor, the storm surge would be very large because there would be more water for less space to spread it out in. However, if the continental shelf is very low, the storm surge will be not as dramatic.