Storm surges are abnormal increases in water levels caused by the force of winds barreling around the eye of the hurricane, the National Hurricane Center (NHC) explains. Water gets pushed onto the shore with violent force, exacerbating the damage caused by vicious hurricane gusts.
Combine these storm surges with the effect of ocean tides, and you get what’s commonly known as the storm tide.
Over a third of property damage expected to be caused by the hurricane will be the direct result of storm surges, estimates real estate analytics firm CoreLogic.
The sheer size of Irma’s hurricane-force winds means that the resulting storm surge could be particularly brutal.
“Along the coast, storm surge is often the greatest threat to life and property from a hurricane,” the NHC says. “In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall.”
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Authorities are well aware of the unique dangers posed by these phenomena, with Miami-Dade County setting up storm surge planning zones using geographical data to determine evacuation plans for different regions.
Storm surges are difficult to predict accurately because they’re highly sensitive to small changes in storm intensity, speed and path, as well as the shape of geographical features such as bays and coastlines.
As of Friday night, the NHC was estimating storm surges higher than nine feet above ground on stretches of Florida’s southern coastline. Miami Beach, located near the southeast tip of Florida, is shielded by a relatively steep continental shelf, which should ensure that the height of the storm surge doesn’t hit double digits.
The NHC estimates that a similarly powerful Category 4 storm striking the Louisiana coastline would be capable of producing 20-foot storm surges. Hurricane Katrina, which caused around 1,000 deaths in Louisiana, brought storm surges of 25-28 feet above normal sea tide levels.
Hurricane Irma is expected to make landfall in Florida on Sunday morning.