Storm surge refers to an offshore rise of water caused by wind and low pressure. This commonly occurs during a tropical cyclone or a hurricane. Storm surges are often mistaken for tidal surges. Tidal surges are violent surges caused by the tidal change in sea level.

Waves during a storm surge usually reach a height of 6 meters (18 feet) or higher, potentially causing severe damage. The 1899 storm surge in Australia is the largest recorded storm surge in history, with waves as high as 13 meters (43 feet). In 2005, Hurricane Katrina caused storm surges that reached 9 meters (30 feet).

The following interacting factors determine the height and power of storm surges:

Strong wind

A storm surge is principally caused by strong wind that blows over the water, which results in violent surges of gigantic waves. The wind moves in a spiral rotational direction, reducing the sea water height downwind and increasing the water height upwind.

The spiral rotational movement of the wind causes the formation of a storm surge. Wind force determines the potential power of the storm surge and the direction of the wind also gives clue as to the direction of the surge.

Low pressure

Another factor that affects storm surge formation is pressure. The water level is lower in a high pressure area since there is much pressure to control the water level.

On the other hand, the water level is higher in a low pressure area because there is not much pressure in counteracting the heightening sea level. Meaning, at the center of the tropical cyclone or hurricane where the pressure is lowest, the effect of the wind is unstoppable and the heightening sea level cannot be controlled.

Heavy rainfall

Rainfall that usually goes with tropical cyclones, hurricanes, as well as other types of storms also affects the formation of storm surges. Heavy rainfall can aggravate the situation - strong wind and low pressure - as it increases the volume of sea water.

High tide

There is a bigger problem if a tropical cyclone or hurricane hits during a high tide since it heightens the water level of the sea. However, it remains unclear for scientists whether the increased sea level is a result of an impending storm surge or whether it is attributed to high tide alone.

Bathymetry

Storm surge formation can also be affected by the depth and terrain of the ocean floor. One critical factor is whether the ocean floor drops off from the shore steeply or not (bathymetry). In other words, a steep drop encourages more powerful and higher storm surges, whereas a sloping floor encourages generally weaker storm surges.