Storm surge

Big storms can push the sea.

Strong winds blow the water toward the land. This causes a flood.

Low air pressure also helps. It lets the water rise up. The shape of the sea floor matters too. Shallow water can make the surge higher.

Rain can make it worse. Rain flows down rivers into the sea. This adds even more water to the coast.

Storms can break roads. They can also hurt buildings. People must be ready for the water.

It is important to have a plan. We can build walls to stop the water.

A storm surge is a sudden rise in sea level. It happens during big storms like tropical cyclones. This rise is not the same as waves. It is the extra water pushed toward the coast.

Many things cause a surge. Strong winds push water toward the shore. This is called wind setup. Low air pressure also helps. When air pressure drops, the water level rises.

The shape of the ocean floor matters too. Deep water lets the surge spread out. Shallow water can make the surge much higher. This is because the water has less room to move.

Rain can also make floods worse. Heavy rain flows down rivers into the sea. This meets the rising ocean water in places called estuaries.

Storm surges can damage roads and buildings. They can even hurt people. To stay safe, towns can build flood barriers. They can also make plans to move people to safety.

A storm surge is a sudden rise in sea level. It is often called a storm flood or a tidal surge. This event is different from waves. It is the extra amount of water that rises above the normal tide. This can happen during big storms like tropical cyclones. These storms can cause huge floods along the coast.

Many things work together to create a surge. High-speed winds push water toward the shore over a long distance. This is called wind setup. Low air pressure also helps the water rise. For every millibar of pressure drop, the sea level can rise. The Earth's rotation also plays a part. This is called the Coriolis effect. It can bend currents toward the shore to make the surge even larger.

The shape of the ocean floor changes how a surge behaves. Deep water lets the surge spread out and lose strength. Shallow water gives the surge less room to move. This makes the water rise much higher. For example, Florida Bay is very shallow. It can experience higher surges than deeper areas. A narrow, steep shelf might produce smaller surges but much larger waves.

Scientists use special tools to study these events. They use pressure sensors to measure water height during a storm. After a storm, they look for high-water marks on land. They also use a computer model called SLOSH. This stands for Sea, Lake and Overland Surges from Hurricanes. It helps experts predict how much water might flood an area. This model looks at storm size and wind speed.

Storm surges can be very dangerous for people living near the sea. They can break roads and damage the foundations of buildings. Heavy rain can also make things worse by flooding rivers. This extra water flows into estuaries from the land. To stay safe, many communities build flood barriers or sea walls. They also use early warning systems to help people move to safety.

A storm surge is a coastal flood caused by a sudden rise in sea level. It is often called a storm flood, a tidal surge, or a storm tide. It is important to distinguish surge from waves. A surge is the rise in water level above the normal tidal level.

While waves move across the surface, a surge represents a massive increase in the total volume of water near the coast. This phenomenon is most commonly associated with low-pressure weather systems, such as tropical cyclones.

Several mechanical processes work together to drive a surge. The most direct cause is wind stress, which leads to a phenomenon called wind setup. High-speed winds push water toward the downwind shore, causing levels to rise there while they decrease on the upwind shore. This movement is influenced by the Ekman spiral, where surface currents move at a 45-degree angle to the wind. This effect spreads vertically through the water column and is proportional to the depth.

Additionally, the low atmospheric pressure at the center of a cyclone allows the ocean surface to rise. For every millibar (hPa) of pressure drop, the sea level is estimated to rise by a corresponding amount. A major storm with a 100 millibar drop would cause a significant rise due to this pressure effect alone.

The Earth's rotation also plays a critical role through the Coriolis effect. This effect bends ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. If this bending brings currents into a more perpendicular contact with the shoreline, it can amplify the surge. Conversely, if the rotation bends the current away from the coast, it may lessen the surge.

Other factors include the rainfall effect, which is most common in estuaries. Large amounts of rainfall from a hurricane can cause surface runoff to flood rivers. This freshwater flows downstream to meet the ocean surge, increasing the total water level.

Geography and topography significantly change how a surge behaves. The shape and depth of the ocean floor, or the bathymetry, determine if a surge is large or small. A wide, shallow continental shelf tends to produce a higher storm surge because the water has less room to disperse. In contrast, a narrow shelf with deep water near the shore produces a lower surge but much more powerful waves.

For example, the shallow Florida Bay experiences higher surges than deeper coastal areas. On the west coast of Florida, the edge of the Floridian Plateau lies much further offshore. In these deeper areas, the surge can be dispersed down and away from the storm center.

Storm size also influences the height of the water. As a storm's diameter increases, its area grows much faster than its perimeter. If a storm doubles in diameter, its area actually quadruples. Because there is proportionally less perimeter for the surge to dissipate through, the surge height can end up being higher. This relationship between area and perimeter makes larger storms particularly dangerous for coastal inundation.

Scientists use several methods to measure and predict these events. During a storm, pressure transducers can be deployed along the coastline to measure the height of the water. After the event, surveyors map high-water marks (HWM) on land to find the elevation of the floodwaters. These marks are compared to tidal predictions to calculate the specific surge height.

To help with planning, the National Hurricane Center uses the SLOSH model. This stands for Sea, Lake and Overland Surges from Hurricanes. The model is accurate to within 20 percent and considers variables like storm track, wind speed, and local topography.

Storm surges pose serious risks to human life and infrastructure. They can destroy roads and undermine the foundations of buildings. Because they can cause unexpected flooding in estuaries, they often catch populations unprepared. To manage these risks, governments use both hard infrastructure, like flood barriers, and soft infrastructure, like mangroves or coastal dunes. Early warning systems and evacuation plans are also vital social strategies for protecting coastal communities.