The “perfect” conditions make Hurricane Helene “unsurvivable”

For the third time in 13 months, a hurricane is tearing through the Gulf of Mexico on a collision course with Florida's northwest coast, threatening a region still recovering from recent extreme weather events with historic storm surges and damaging winds stretching hundreds of miles.

But Hurricane Helene, which followed last year's Hurricane Idalia and last month's Hurricane Debby, is no ordinary storm, even by Florida standards. Like other climate-related storms in recent years, it is expected to undergo what is known as “rapid intensification,” increasing in strength at a phenomenal rate as it passes through the Gulf's exceptionally warm waters. Therefore, it is likely to make landfall as a Category 3 or 4 storm just days after it first forms in the Caribbean. It has also become one of the most powerful storms on record, bringing life-threatening winds and rain as far inland as Tennessee.

Hope Webb, a real estate agent who lives in a beach area of ​​the state's sparsely populated Big Bend region, said Thursday that she is hunkering down and hoping for the best as the storm is expected to make landfall later in the evening.

“I’ve lived in this area my whole life,” she told Grist. “I have weathered many a storm. I have faith that God will put his arms around us. But this storm is definitely testing our strength.”

Three factors combined to make Helene a particularly powerful storm. Like any hurricane, its fuel is warm seawater, which releases energy into the atmosphere as it evaporates. As Helene moved through the Caribbean Sea, she fed on exceptionally warm ocean temperatures, which experts say have been made at least 300 times more likely by climate change. As it continued its march north toward the Gulf Coast, it gathered power from water that is both unusually warm and deep — a vast pool of high-octane fuel.

Additionally, wind shear — a term that refers to the tendency of winds to move in different directions and speeds at different altitudes — was low in the region. This atmospheric disorder would normally lower the strength of a hurricane. Finally, the high humidity was another factor that affected Helene.

“The conditions were almost perfect,” said Karthik Balaguru, a climate scientist who studies hurricanes at the Pacific Northwest National Laboratory.

The combination of warm and deep ocean fuel, high humidity and low wind shear has put Hurricane Helene on the cusp of rapid intensification, which technically means an increase in sustained wind speeds of at least 35 miles per hour within 24 hours. Scientists have noticed a dramatic increase in the number of rapid intensifications near coasts in recent decades.

“The clear signal of climate change is that it is increasing the proportion of intense hurricanes,” Balaguru said. “Storms tend to intensify more quickly and especially near the coast.”

This makes hurricanes more dangerous than ever. For one thing, a coastal city may be preparing for an approaching Category 1 hurricane, only for it to suddenly turn into a Category 3 hurricane. Far beyond the coast, the stronger a hurricane is, the better it can resist dissipation as it moves over land and loses its fuel source. And as the atmosphere warms, it can also hold more moisture, allowing hurricanes to drop more rain.

What makes a storm like Helene so dangerous for coastal communities is not just the winds and rainfall, but also the storm surge. A hurricane's winds wash water onto the coast – a dangerous outcome for a region like the Gulf Coast, where sea levels are already rising.

The geography of Florida's west coast makes matters worse. While the depth of some beach areas decreases precipitously just offshore, the depths here gradually increase as you move further from shore. If the water near the coast were deeper, a storm surge could be partially absorbed by those depths, lessening its impact on land. But with water so shallow off Florida, the water can only flow directly into coastal communities.

Although the eye of Helene is expected to make landfall near Tallahassee on Thursday evening, a hurricane's strongest winds tend to blow in the northeastern part of the storm. For Helene, those winds are poised to hit Florida's less developed Big Bend region, which also suffered the worst impacts of Idalia last year. This part of the state is extremely low-lying, allowing the storm surge to move inland without being impeded by geography that typically presents mitigating factors. The forecast flood could reach as high as 20 feet in towns like Steinhatchee, south of Hope Webb, who is weathering the storm at her beachfront home. In an announcement Wednesday evening, the National Weather Service office in Tallahassee called these conditions “catastrophic,” “potentially unsurvivable.”

Further south, the populous Tampa Bay region is also expected to see record increases after decades of near misses. “Just the shape of the coastline in this area definitely makes it easier for that storm surge to build up,” said Samantha Nebylitsa, who studies hurricanes at the University of Miami. “It kind of flows into Tampa Bay, and so the water really has nowhere to go except into that area.” In many cases, estimates suggest Hurricane Helene will break storm surge records by more than two feet.

Early Thursday, the storm was still hours away from passing over St. Petersburg, but winds had already picked up and the sky was darkening. Several downtown gas stations ran out of fuel as residents filled their tanks, and most people in low-lying areas had secured their homes against flooding with sandbags, tarps or door sealants. Flashing signs reading “HIGH WATER EXPECTED” warned motorists to stay away from the coast. Counties along the Gulf Coast, including the cities of Tampa and St. Petersburg, had ordered mandatory evacuations for residents of storm surge areas and those living in mobile and manufactured homes. Localized flooding has already occurred on the streets of the beach town of Clearwater.

Hurricane Helene is a massive storm — its wind field is more than 400 miles across — so its rain will fall from the coasts of Georgia and the Carolinas well into Missouri and Arkansas. As of early Thursday, all counties in South Carolina, Georgia and Tennessee were under some type of flood or wind warning. Forecasters are warning of flash flooding, particularly in the mountainous regions east of Knoxville and Chattanooga, Tennessee, as the storm subsides, and damaging winds that could cause widespread power outages in Georgia.

Like a car accelerating to a higher speed, Hurricane Helene can slide further inland without running out of momentum, given how much speed it has gained as it travels through the Gulf's particularly hot waters.

“It will basically just hurl itself into these states,” Nebylitsa said. “And at this rate, it’s going to take a lot longer to slow down.”

All of these regions, whether coastal or inland, have significant development that is particularly vulnerable to flooding. Along Florida's coast, there are thousands of homes on low-lying coastal land that are easy prey for storm surges, and states like Georgia and North Carolina have built thousands of homes near rivers and streams that are likely to be inundated if Helene passes over the coast moves. The more frequently strong hurricanes like Helene occur, the more these vulnerabilities become apparent.

“We're entering this new normal of what we're going to experience with climate change,” said Michelle Meyer, director of the Hazard Reduction and Recovery Center at Texas A&M University. “But secondly, we have been continuing to build in really risky places for a long time, in ways that are also pretty risky. So if we continue to add more and more homes in areas that regularly flood, or add more homes on the coast without the need for major remedial work, we will see greater and greater dangers.”

Ayurella Horn-Muller contributed to this article.