How Hurricane Helene became a deadly disaster in six states

Some hurricanes are remembered for their wind damage or rainfall. Others because of their coastal flooding. Hurricane Helene was a stew of all of the above and more. Its near-record size, storm surge, winds and rainfall combined to make Helene an almost unimaginable disaster that stretched more than 500 miles inland from the Florida coast.

At least 230 people died in Florida, Georgia, South Carolina, North Carolina, Tennessee and Virginia as Helene flooded towns, destroyed roads and bridges and ripped away homes.

In Florida, the storm surge from Helene caused damage to hundreds of kilometers of coastline. While residents were clearing up debris there, another dangerous hurricane was approaching them. Some of the same areas hit hard by Helene on September 26, 2024 – including Tampa Bay and Cedar Key – were expected to experience further flooding and an even stronger storm surge in Tampa Bay from Hurricane Milton, which is expected to make landfall as early as October becomes . 9.

Most of Helene's victims were far from the coast and were caught by surprise when the storm dumped more than 20 inches of rain on the mountains, quickly turning streams and rivers into torrential torrents.

I study hurricane history as a geographer and climatologist in one of these hardest hit states, South Carolina. Helene was by far the deadliest inland hurricane of all time, surpassing Hurricane Agnes in 1972, which killed 128 people in the northeastern United States. And it was the third deadliest on the continental United States since operational forecasts began in the 1960s, after Hurricanes Katrina (2005) and Camille (1969).

Meteorologists routinely assess three main components of hurricanes: wind intensity, storm surge and rain. Here you can see how these elements, along with Helene's enormous size and forward speed, made the storm far more destructive than its wind speed alone suggested.

Helene's destructive winds

Helene was undoubtedly the strongest hurricane to hit Florida's Big Bend area north of Tampa since 1851. It made landfall late on September 26 near Perry, Florida, as a Category 4 hurricane with sustained winds of 140 miles per hour.

The storm's rapid forward motion – it moved northward at about 30 miles per hour after making landfall – and its size meant that Helene's winds were still strong as it reached Georgia and South Carolina, areas that rarely experience such damaging winds Winds occur. More than two million homes lost power across the two states, and more than a quarter million of them were still without power a week after the storm.

Valdosta, in southern Georgia, was hit by near Category 2 winds, with speeds around 90 to 95 miles per hour. The city has experienced only a few hurricanes in the last century, including Idalia in 2023. Augusta, on the other side of Georgia near the South Carolina border, experienced sustained tropical storm gusts with speeds of up to 69 miles per hour.

Storm surge almost record-breaking

Helene's size was an important factor. The hurricane was huge – about 400 miles wide, similar in size to Hurricane Katrina and one of the largest to make landfall in the continental United States

This size contributed to Helene's destructive storm surge. Hurricanes push on the sea, creating a storm surge that can inundate the coast with water several feet above normal sea level. Large, strong storms impact a larger area of ​​ocean over a longer period of time and build up a larger storm surge.

Initial estimates were that Helene's storm surge peaked at about 15 feet in the Big Bend area. This would make it one of the highest storm surges recorded in the region since the mid-19th century. Field surveys will take several weeks to verify elevation.

Cedar Key, Florida, about 50 miles east of central Helene, experienced a storm surge of about 9.3 feet, which would be the highest storm surge since the early 20th century. Three higher storm surges have been reported in this area in the past: 12.5 feet in 1896, and about 15 feet each in 1842 and 1848.

Tampa Bay, nearly 200 miles south of Helene's center, experienced a destructive storm surge of over 6 feet. There were worse things in the Tampa area, including a 15-foot storm surge in 1848, but Helene's damage was still extensive there. Twelve people died in the storm near Tampa.

Rain and floods in the mountains

Much of Helene's most devastating impact occurred far inland as the storm moved up the mountains.

Normally, fast-moving storms present a lower threat of rain, but Helene was a major exception. In the southern Blue Ridge Mountains, Helene's rain was enhanced by the terrain and what is known as orographic uplift. When a storm is forced to climb up a mountainside, the air cools and condenses, causing more precipitation to fall.

In the mountains, precipitation flows quickly into streams and rivers. Asheville, North Carolina, a rapidly growing city of about 95,000 residents, sits in a depression in mountainous terrain. This made it and other nearby towns very vulnerable to high river flows and extreme flooding. What made matters worse was that the area just before Helene was already saturated by a storm.

The French Broad River crested at 24.67 feet near Asheville, breaking the previous record of 22 feet set in 1916, also caused by hurricane remnants.

In South Carolina, the storm was so large that its rain bands covered the entire state. The National Weather Service in Greenville-Spartanburg reported that 8 to 2 feet of rain fell in the state of South Carolina.

Atlanta reached 11.2 inches in 48 hours, setting a record.

Assessing Hurricane Risk in a Warming World

Helene's devastation is an important reminder that hurricanes cannot be judged by wind speed alone. The commonly used Saffir-Simpson scale, which classifies storms into categories 1-5, is based primarily on wind intensity. Helene was classified as a Category 4 storm, but its damage was comparable to some of the most destructive hurricanes in history.

As the climate warms, the risk of hurricanes changes. Warmer ocean water fuels hurricanes, and warmer air can hold more moisture, leading to stronger, more destructive storms. The exceptional rainfall in Helene and the consequences could be a sign of future hurricanes.