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Why is Hurricane Laura so frightening? Two words: storm surge

August 26, 2020, 11:14 PM UTC

As Hurricane Laura barrels toward the Louisiana-Texas border this evening, the massive category 4 storm is almost certain to pound a vulnerable stretch of coastline with cannonballs of air, as sustained 145 mile-an-hour winds flatten much of what lies in their way. But the bigger threat—a potentially “unsurvivable” one, according to the National Hurricane Center—will be the storm surge, and that’s partly because of where this cyclone is headed.

Laura is tracking closely in the path of another killer storm 15 years ago—Hurricane Rita—which slammed the Gulf Coast less than a month after Hurricane Katrina. “Hurricane Rita was kind of forgotten about, given the epic destruction of Katrina just before it, but it was also devastating—and Hurricane Laura is pretty much on track to follow it,” says Hermann Fritz, a professor at Georgia Tech’s School of Civil and Environmental Engineering, who has studied the effects of both Katrina and Rita.

Hurricane Laura, which at 4 p.m. Central time was about 155 miles away from both Port Arthur, Texas and Lake Charles, La.—and could veer toward either bull’s eye by landfall Wednesday night or early Thursday—was likely to bring catastrophic, high-velocity flooding in either case. “This is a territory where 20-foot storm surges for up to 30 miles inland are very possible,” Fritz says.

A massive storm surge approaching Lake Charles could be particularly costly given the energy infrastructure around Calcasieu and Sabine Lakes, where some three-quarters of export capacity for liquefied natural gas is centered in the United States, and where oil refineries and a major fishing industry are located.

If Hurricane Laura follows Rita as expected, then its heaviest winds to the right of the eye wall—the vertical wall of clouds surrounding the eye of the storm—will drive right into Calcasieu Parish, says Fritz. “The problem is, the Calcasieu Ship Channel that goes up to Lake Charles is exactly perpendicular to the shoreline, which means it’s aligned with the advancing storm,” he says. “It will be a perfect match for the storm surge to maximize its effect along that path.”

Nearly all of the storm surge from major hurricanes come from the winds generated by the eye rotating counterclockwise, which are most fierce to the right of the eye wall. Right now, as Hurricane Laura drives to the coastline at 15 miles per hour, it’s pushing the Gulf water towards the shore. Though that can generate huge waves offshore, it doesn’t do too much in terms of raising sea level far away from the coast, says Fritz. But when you get to shallow water, the effect is suddenly pronounced—particularly in the Gulf of Mexico, which has a very wide continental shelf and a very shallow coastline. “The water has nowhere to escape,” he says. “It’s trapped. It gets pushed to the shore and the wind is blowing over it and piling up the water towards the shoreline. Then you get to the Calcasieu River and that navigation channel—and then to Calcasieu Lake, which is also super shallow—which amplify the surge as they form an artery straight up to Lake Charles. Take all that into consideration and we can have inundation 30 miles inland.”

“We’re going to see storm surge in the order of 20 feet, potentially all the way up to the city of Lake Charles, all the way up there,” Fritz predicts. “It will be quite dramatic.” But the destruction doesn’t just come from the rising water level, he points out, it’s also due to the speed and force of that fast-moving water. “You get current velocity, you get flow velocity, overlap flow velocity—all of which is capable of washing things away,” he says.

In the 15 years since Hurricanes Katrina and Rita walloped the area in back-to-back blows, we’ve built some protective infrastructure on this vulnerable coastline—but in only a few places. “Humans have a tendency to fight the last war,” says Fritz. So significant barriers and fortifications were built around New Orleans, but not so much around Calcasieu. “But we have gotten much better at forecasting these hurricanes,” he says. “And evacuations. So there’s at least time to get out of the way.”