Why Hurricane Florence is Unusual and Dangerous
Updated September 14, 2018 at 4pm
With 90-mile per hour winds and 10-foot storm surges, Hurricane Florence started battering the Carolinas on Thursday morning. Forecasters are warning that some areas could receive up to 40 inches of rainfall. Already, more than 300 people have had to be rescued from flooded homes, and four deaths are linked to the storm, which is expected to persist into early next week.
At the Earth Institute, hurricane and disaster experts are closely monitoring the situation. Below, they explain what makes Hurricane Florence unusual, and unusually dangerous.
Hurricane and disaster experts within Columbia’s Earth Institute are available to answer questions from the media about hurricane physics, emergency response, the role of climate change in creating strong storms, and more.
Why Hurricane Florence is Unusual
It’s somewhat rare for hurricanes this intense to make landfall in the Carolinas, said Suzana Camargo, executive director of the Initiative on Extreme Weather and Climate at Columbia’s Lamont-Doherty Earth Observatory. “It’s a not a typical track,” she said, referring to the storm’s expected path. Normally hurricane trajectories curve backwards toward Europe, sending the storm back into the ocean. Not so for Florence—simulations show it making a beeline for the Carolinas.
“Hurricanes basically go with the winds,” Camargo explained. “The winds take them where the winds are going… When you have areas of high pressure, that’s where hurricanes don’t go. Right now we have this very strong high in the Atlantic that’s not allowing the storm to recurve.”
Why Florence Was Difficult to Predict
In the days leading up to the storm, what concerned Camargo most was that the forecasts for what would happen as Hurricane Florence approached the coast had been very uncertain. Different models showed different predictions for exactly where the storm would go, whether it would make landfall, and how slow it would be moving. That’s due to a second high pressure system in the Midwest, similar to the one in the Atlantic, which also wanted to push the hurricane away.
“To determine where the hurricane will go, we have to predict which high is going to be stronger,” said Camargo. “It’s like they’re competing, and it depends on the winds and what’s happening in the storm.”
It was also difficult to predict exactly how strong, or intense, Hurricane Florence will be. Hurricane scientist Chia-Ying Lee from the International Research Institute for Climate and Society at Columbia’s Earth Institute explained that hurricane intensity change depends on large-scale factors like the vertical structure of the winds and ocean temperatures, as well as small-scale processes such as thunderstorms within the hurricane. “These processes are not fully understood,” she wrote via email. “The smaller scale features are not well observed, and are chaotic in nature. Thus, it is harder for computer models to have good representation of these processes and accurately predict storm intensity change. So, while we often know whether a storm is going to intensify or weaken (because we know the large-scale conditions), exactly how much a storm intensifies or decays is less predictable.”
The Potential Impacts
While Hurricane Florence’s exact trajectory and intensity were uncertain, scientists warned that the storm would pose a significant threat to the Carolinas in all scenarios, in large part because of the slow-moving nature of the storm.
Radley Horton, a climatologist at Lamont-Doherty said that where the storm slows down would be critical. “Unfortunately, it currently appears this will occur close enough to land to inflict serious storm surge flooding,” he warned on Wednesday. “The slow movement, should it indeed happen near shore, would virtually guarantee that the storm surge coincided with at least one, and possibly more than one ‘astronomically’ high tide, leading to further ocean flooding and accumulated wave damage.”
Earth Institute experts also noted that Hurricane Florence would likely bring intense rainfall. Slowing or stalling near the coast would increase flood hazards, “because there’s more time for winds to drive surge and more accumulated rain,” explained Tim Hall, who models hurricane risk at the Earth Institute-affiliated NASA Goddard Institute for Space Studies.
There is a high to moderate risk of flash flooding from #Florence across eastern North Carolina and extreme eastern South Carolina on Friday. @NWSWPC is forecasting more than 20″ of rain in some areas over the next week. https://t.co/krDhlpZ8LX pic.twitter.com/YhIH0JziC0
— National Hurricane Center (@NHC_Atlantic) September 12, 2018
“Significant effects could also be felt as far inland as parts of Tennessee, Kentucky, Alabama and West Virginia,” Jeff Schlegelmilch and Irwin Redlener from Columbia’s National Center for Disaster Preparedness warned in The Hill. “This could lead to flash flooding and damaging winds further inland. Additionally, an influx of people evacuating from the storm or traveling for supplies could lead to temporary shortages of fuel and other necessities, as has been seen in the aftermath of other storms.”
What Role Did Climate Change Play?
“The airtight link between Florence and climate change is through sea level rise,” said Horton. “Coastal Carolina and Virginia have experienced approximately a foot of sea level rise over the past century, the majority of which is due to human-driven climate change. As a result, when a storm like Florence occurs, additional areas are flooded by the sea that would not have flooded had human activities not melted land-based ice and warmed the ocean, causing it to expand.”
In addition, warmer oceans can add more energy into hurricane systems. Meanwhile, a warmer atmosphere is able to take up more water vapor, leading to more intense rainfall later.
Lastly, “there’s evidence that a warming climate is slowing the large-scale wind patterns that steer storms,” said Hall. He cites a recent paper in Nature that found that hurricanes are traveling around the planet more slowly. “I’d expect this slow-down to be realized as more frequent stalls and abrupt changes in direction,” he said. “Harvey last year is an example, and Florence could be, too.”
Addressing the Challenges that Lie Ahead
Schlegelmilch and Redlener praised Virginia’s and the Carolinas’ disaster preparation and mandatory evacuations in low-lying coastal areas, but warned that recovery from the storm could be long and challenging.
While the nation needs to improve on disaster preparedness as well as disaster response and recovery, Earth Institute director Alex Halliday reminded us that taking action on climate change will also help to spare lives and human misery in the future.
“Climate change is expected to result in increased numbers of very intense storms like Hurricane Florence,” he said. “With higher temperatures, it is not surprising that there would be more evaporated water and energy in the atmosphere. To limit the future loss of lives, homes, and billions of dollars in damages, we need to address climate change at the local, state, and national levels. Within Columbia’s Earth Institute, researchers are using advanced modeling techniques to understand today’s storms and to predict what future ones might look like. We are testing the effectiveness of sea walls, recommending recovery processes after disasters, and finding innovative ways to decarbonize our society. If all parts of society can come together on a united front, we can better deal with the weather challenges that lie ahead.”