(This article has been updated with the latest information.)

While we often focus on wind speeds when hurricanes draw near, one of the most dangerous and destructive components of these storms is the surge of water that floods the shoreline and pushes upstream into rivers and bays at landfall.

Tropical Storm Helene is expected to strengthen into a major hurricane, prompting hurricane and storm surge watches across much of Florida’s Gulf Coast as it moves northward from the Caribbean into the Gulf of Mexico.

The sudden influx of water combined with powerful waves can create immense damage, sweeping homes from their foundations and inundating low-lying regions even miles inland.

Understanding storm surge

In the deep sea, hurricane winds push water towards the center of the storm. Instead of accumulating, the water spirals downwards and spreads outward.

As water is forced downward, some flows out into the ocean, while some moves toward the coastline.

When the storm nears land and enters shallower waters, the ocean floor obstructs the outflowing water. This causes the water to surge onto land.

The Gulf of Mexico’s heightened risk for storm surge

The ocean bottom and the coastal shape can greatly affect the height of storm surge—which is the difference in water levels as a storm approaches. The soft, gently sloping continental shelves in the Gulf of Mexico make the region particularly susceptible to water buildup. In contrast, the narrower, steeper shelves of the Atlantic coast generate a lower surge.

Other factors include the size and speed of the hurricane. A rapidly moving hurricane tends to produce a higher surge when hitting an open coastline. However, if a slower storm approaches an enclosed bay like Tampa Bay on Florida’s Gulf Coast, the surge can be larger.

Storm surge is just one element contributing to higher water levels. When a storm coincides with a lunar high tide, those water levels will be elevated even further. Together, the surge and tide create what is termed storm tide.

(This article has been updated with additional details.)