How hurricanes cause catastrophic flooding

For the first time in decades, the Carolinas faced what was, at its peak, a major category four hurricanes with the potential to rip homes from their foundations. Over a million residents were instructed to evacuate eastern North Carolina in the days leading up to the storm, finding temporary places to stay in Charlotte, Winston-Salem, Atlanta, or other inland cities distanced from the coast. The media began preparing everyone for the devastation blowing in, but on Thursday, September 13th more and more residents refused to flee as wind speeds started to fall.

In the days leading up to the storm, wind speeds decreased from one hundred and forty miles per hour to under one hundred miles per hour. Instead of retreating to a friend’s home, temporary rental, or a pet-friendly hotel with a kitchen, many people stayed in their house and ignored the threat. On Friday, September 14th Florence was thought to be ‘just a category one by many locals, and little focus was put on the potential destruction of flooding. Heavy clouds rolled over the states, moving at less than three miles per hour, pouring gallons and gallons of rain on the streets, homes, farms, and rivers of the Carolinas.

As we’ve seen with recent hurricanes like Harvey and Matthew, Florence slowed down significantly as it approached land, which decreased the threat of wind damage but increased the threat of water damage. Many people fail to realize that the severity rating of hurricanes is based solely on wind speeds and not on a more sophisticated combined measurement for predicting damage. Hurricane-force winds start at seventy-four miles per hour. Storms that reach this speed are classified as hurricanes, though in the Pacific Ocean they are usually called “typhoons.” Many U.S. homes are insured for hurricane (or wind-related) damage but not flood damage, so flooding from Florence will likely impact the National Flood Insurance Program and local economy more than the insurance industry as some displaced homeowners look to FEMA and the Red Cross for aid.

The Atlantic reported that Florence would drop eighteen trillion gallons of rain on North Carolina, equivalent to the volume of the Chesapeake Bay, but otherwise, the media focused mostly on storm surge and the “category” of the storm. New Bern, North Carolina was the first place to see major flooding. Soon after, parts of Wilmington, Leland, and Jacksonville received upwards of thirty to forty inches of rain over a large span of low-lying land. Much of the water dumped on North Carolina would later flow south. While Florence sat over the states for more than two days, thousands of homes were damaged by water, and thousands more still remain under threat.

The “Storm of the Century” that decreased from a category four to a category one over the Atlantic never lost its deadly power, that destructive power was simply converted. The NOAA reports that the majority of hurricane-related deaths are the result of freshwater or saltwater drowning, and not because of wind, tornadoes, electrical, or other threats that accompany a hurricane. At last count, forty-eight people had died because of Hurricane Florence, many relating to freshwater flooding, drowning, or cars being swept off the street by heavy rains and flash flooding.

The Saffir-Simpson Hurricane Wind Scale that gives us our five-category hurricane scale is the most commonly used indicator of the predicted severity of a storm, but now it’s being questioned, as it may have led some people to take this storm less seriously than they should have. Category four hurricanes will almost always cause more immediate property damage than category one or two hurricanes, but the loss of life and total long-term effect of a storm is more accurately measured by the amount of water dumped on an area and that area’s geographic layout.

Flooding is typically the longest-lasting effect of a hurricane, but in visual models, we usually see visualizations of storm surge rather than a flash flood. Storm surge occurs when a hurricane pushes water outward, causing the sea level surrounding the storm to rise before making landfall. Television meteorologists often show visualizations of storm surge lifting vehicles on city streets. While a sizeable surge was seen on the coast, it was ultimately not as damaging as the subsequent flooding from torrential rainfall more inland.

During Hurricane Katrina, the storm surge broke the levees of New Orleans leading to major flooding and preventing many citizens from evacuating the city. Since Katrina, the storm surge has been one of the most concerning threats during a hurricane. North Carolinians were given more warning for Florence than citizens in New Orleans were given in 2005. A larger portion of the population in North Carolina escaped before the worst of the storm, but still, the downgrading of Florence may have led more people to ignore evacuation orders and put more responsibility on first responders to save those stranded in rising floodwaters.

Some homeowners forced to evacuate have made claims for temporary housing until they can return home after repairs are made. Before the storm made landfall, Sedgwick’s temporary housing division had begun locating hotels and suitable temporary housing for our adjusters and their customers. Our CAT team was able to get into Wilmington before most response teams and immediately began assisting property adjusters and first responders in rebuilding the community.

Inland flooding will remain a major issue because much of eastern North and South Carolina is relatively low in elevation. The landscape of where a storm makes landfall contributes heavily to the way that storm proceeds in severity and damage to life, land, and property. While the coast received up to thirty inches of rain in some areas, cities as far west as Raleigh had more than ten inches dumped on them, causing flash flooding to be a major issue and the trickledown effect to flood numerous towns days after the storm had ended.

For the moment, New Hanover County and the city of Wilmington have become an island, cut off from the rest of the state by the downpour that was Florence now moving toward South Carolina and returning to the sea. Sedgwick’s temporary housing division CAT Response Team and others continue assisting those returning to homes battered and destroyed. We will be here for the long run, rebuilding communities with the citizens who call them home.