Hurricane Florence storm surges will be amplified by sea level rise

Surging hurricane waters can throw around cars, boats, and houses like toys. 

Six years ago, Hurricane Sandy pushed storm surges into the streets of Staten Island, New York, wrecking entire neighborhoods along the small island off the coast of Manhattan. Homes are still being rebuilt, and some have simply been abandoned.

Now, a more powerful tempest, Hurricane Florence, is set to hit the Carolinas late Thursday with winds reaching some 120 mph.

Regardless of exactly where it makes landfall, the storm’s mass of winds will be destructive, forcing high surges of ocean water into coastlines, barrier islands, and neighborhoods. 

And the storm surge may be even worse due to the effects of human-caused climate change.

The oceans off the southeastern coast of the U.S. have risen by about 9 inches in the last 100 years, boosted by some of the most visible manifestations of global warming, namely melting ice sheets and expanding oceans. 

In light of this reality, how much worse might these Florence-caused storm surges be?

“The simplest effect is that any storm surge is amplified by sea level rise,” Jaap Nienhuis, a researcher at Florida State University’s Coastal Morphodynamics Lab, said in an interview.

“When a major event like this occurs, it’s riding on top of sea level rise,” added Rick Luettich, the Director of the Institute of Marine Sciences at the University of North Carolina at Chapel Hill, in an interview. 

Sea level rise can certainly make the difference in whether or not hurricane waters surmount coastal dunes and comes flooding into communities, said Luettich, but it’s not yet as influential as normal tides in determining how a destructive a storm’s surge may, or may not, be. 

Off the North Carolina coast, tides rise and fall between 5 and 6 feet each day — substantially more than current contributions from sea level rise.

“The timing of the surge with the tide is enormously important,” said Luettich. “We might dodge the bullet if it [Florence} were to hit at a low tide.” 

Yet, a looming problem with Florence is that the expansive storm is expected to stall over the region — as more storms are want to do as the Arctic warms. 

This means strong winds could have more opportunities to hit the high tide cycle, bringing the worst of the surges.

“If it’s a real lingerer, then it will undoubtedly end up going through a high-tide cycle,” said Luettich.

The future of storm surges

Any storm surge is dependent on a variety of factors — the shape of the land, winds, tide, etc. — and sea level is just one component. 

But sea level rise is now accelerating as ice sheet melt hastens and the warming ocean expands. Eventually, sea level rise will be a critical influence.

“The effect today is not nearly what it’s going to be in 100 years,” said Hugh Willoughby, a hurricane researcher at Florida International University. “Down the road — when the sea has risen a meter — then it’s going to be a factor.”

Until then, however, sea level rise will still be a growing, relentless problem.

Melting ice and expanding oceans “are going to persistent into the future,” Ben Hamlington, NASA’s Sea Level Change Team Lead, said in an interview. “You know they’re going to contribute going forward.”

A NASA graph showing sea level rise since 1993.

And as the surges grow, development along the coast has largely eliminated the natural barriers that once weakened storm surges — things like marshes and dunes. 

“There’s not a buffer zone anymore,” said Nienhuis. “It’s been developed immensely,” he said, specifically citing the Southeastern coastline.

To counteract the disappearance of natural barriers, we’ve built impressive fortifications like seawalls to combat rising seas or surges, said Nienhuis. 

But these efforts are counter-intuitive, he said. Rigid walls reflect wave energy, rather than absorbing it, sending that energy to other portions of the coast, and bringing erosion and damage elsewhere.

Hurricane Florence promises to be such a powerful tempest that it’s wise — if not imperative — to leave the coasts, should the right combination of high tides, surging waters, and ever-growing sea level rise combine to hammer coastal communities. 

Willoughby says it would behoove coastal dwellers to take a trip well inland — perhaps using the storm as an excuse to really get out of town.

“There’s a lot of people in the coastal Carolinas that should be thinking about visiting Aunt Mabel in St. Paul, Minnesota,” he said.