Tutorial
Lesson 2
Understanding the Event
What is a Storm Surge?
A storm surge is a rise in the level of seawater that is caused by strong winds pushing the water onshore. The flooding caused by this can be devastating and, so the greatest risk from storm surge is to coastal communities. However, a large strong surge can reach up to a kilometer or more inland like a very large wave.
The figure on right shows how a storm surge forms.
Above the equator, typhoon winds rotate counter-clockwise. The figure illustrates a situation when winds in the northern half of the typhoon are blowing to the west and, so, pushes seawater onshore in the eastern coast of a country. The situation can be reversed on the western coast, when the southern half of the typhoon blows seawater onto the shore.
What is a Storm Surge Like?
Storm surge survivors report different things occurring during the storm surge. In some cases, as the eye moves through an area, the direction of the wind changes. This can cause the shore to recede initially, as the winds push the water away from the land. And, then, when the wind changes, it can start pushing the water in the other direction, onto the land, forming a storm surge. This was reported by some eyewitnesses during Typhoon Haiyan.
The storm surge can develop rapidly. In some cases, the weather can seem calm, even sunny, hours before the typhoon arrives. But when the winds begin gathering strength, the storm surge can form very quickly, rising several meters in a matter of minutes. This is why people get trapped, as they assume they can wait until the last minute to flee the coastal area.
