For the third time in 13 months, a hurricane is spinning through the Gulf of Mexico on a collision course with Florida’s northwest coast, threatening a region still recovering from recent extreme weather with historic storm surges and dangerous winds spanning hundreds of miles.
But Hurricane Helene, which follows last year’s Hurricane Idalia and last month’s Hurricane Debbyis no ordinary storm, even by Florida standards. Like other high-profile climate-driven storms of the last few years, it is expected to undergo what meteorologists call “rapid intensification,” gaining strength at a phenomenal rate as it moves through the unusually warm waters of the Gulf. As a result, it is poised to make landfall as a Category 3 or 4 storm just days after it first formed in the Caribbean. It also ballooned to become one of the most widespread storms on record, which would allow it to bring 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 she was gutted and hoping for the best as the storm is expected to make landfall that evening.
“I’m a lifelong resident of this area,” she told Grist. “I have weathered many a storm. I believe that God has his arms around us. But this storm is definitely testing our strength.”
Three factors conspired to make Helene a particularly powerful storm. Like any hurricane, its fuel is warm ocean water, which injects energy into the atmosphere as it evaporates. As Helene moved through the Caribbean, it at least fed off of unusually warm ocean temperatures that had been created 300 times more likely due to climate changeaccording to experts. As it continued its march north toward the Gulf Coast, it gained power from water, both of which are unusual warm and deep – a large pool of high-octane fuel.
In addition, the region’s wind shear — a term that refers to the tendency of winds to move in different directions and speeds at different altitudes — was low. That atmospheric messiness will typically put a lower ceiling on a hurricane’s strength. Finally, high humidity was another ingredient that worked in Helene’s favor.
“It had almost perfect conditions,” said Karthik Balaguru, a climate scientist who studies hurricanes at the Pacific Northwest National Laboratory.
The combination of warm and deep-sea fuel, high humidity and low wind shear put Hurricane Helene on the verge of rapid intensification, which technically refers to an increase in sustained wind speed of at least 35 miles per hour within 24 hours. Scientists have a dramatic increase in the number of rapid intensifications near the coast in recent decades.
“The clear sign of climate change is that it increases the ratio of intense hurricanes,” Balaguru said. “Storms tend to intensify faster, faster and especially near the coast.”
This makes hurricanes more dangerous than ever. For one, a coastal city can prepare for an approaching Category 1 hurricane, only for it to suddenly turn into a Category 3. Far beyond the coast, the more powerful a hurricane is, the better it can resist dissipating as it moves over land. and lost its source of fuel. And as the atmosphere warms, it can also hold more moisture, so hurricanes can dump more rainfall.
Photo by Joe Raedle/Getty Images
For coastal communities, what makes a storm like Helene so dangerous is not only the winds and rainfall, but also the storm surge. A hurricane’s winds push water ashore—a dangerous outcome for a region like the Gulf Coast, which is already experiencing sea level rise.
The geography of Florida’s west coast only makes things worse. While the sea depths of some beach regions drop right off the coast, here the depths gradually increase if you move away from the coast. If the water near the coast was deeper, a storm surge could be partially absorbed by these depths, mitigating its impact on land. But with such shallow water off Florida, the water has nowhere to go but straight to coastal communities.
Although the eye of Helene is expected to make landfall around Tallahassee on Thursday evening, a hurricane’s strongest winds tend to blow in the northeast part of the storm. For Helene, those winds are poised to hit Florida’s less developed Big Bend region, which also took the worst impact from Idalia last year. That part of the state is extremely low lyingso that the storm surge can rush inland, unhindered by the kinds of geographic features that would normally be mitigating factors. The projected surge could reach as high as 20 feet in towns like Steinhatchee, just south of where Hope Webb is riding out the storm at her beachside home. In an announcement Wednesday night, the National Weather Service office in Tallahassee called these conditions “catastrophic” “potentially unsurvivable.”
Further south, the populous Tampa Bay region is also poised to see record boom numbers after decades of near misses. “Just the shape of that coastline in that area, it definitely makes it easier for that storm surge to pile up,” said Samantha Nebylitsa, who studies hurricanes at the University of Miami. “It kind of runs into Tampa Bay, and so there’s really nowhere for the water to go but in that area.” In many cases, estimates indicate that Hurricane Helene is on its way break climbing records by more than 2 feet.
As of early Thursday, the storm was still hours away from passing over St. Petersburg, but winds had already begun to pick up and the sky was darkening. Several gas stations in the city’s downtown area ran out of fuel as residents filled their tanks, and most people in low-lying areas shored up their homes against flooding with sandbags, tarps or door sealants. Flashing signs reading “HIGH WATER EXPECTED” warned drivers to stay away from the shoreline. Counties all along the Gulf Coast, including those surrounding the cities of Tampa and St. Petersburg, issued mandatory evacuations for residents in storm surge zones and those living in mobile and manufactured homes. Streets in the beach town of Clearwater have already seen localized flooding.
Jake Bittle / Grist
Hurricane Helene is a massive storm — its wind field is more than 400 miles across — so its rain will fall from the coastlines of Georgia and the Carolinas clear into Missouri and Arkansas. As of early Thursday, every county in South Carolina, Georgia and Tennessee was under some kind of flood or wind warning. Forecasters are warning of flash flooding, especially in the mountainous regions east of Knoxville and Chattanooga, Tenn., as the storm stalls, and of dangerous winds that could cause widespread power outages across Georgia.
Like a car accelerating to a higher speed, Hurricane Helene can drive further inland without running out of momentum, given just how much speed it picked up as it passed through the extra warm Gulf waters.
“It will essentially just shoot itself into those states,” Nebylitsa said. “And at that speed, it will take a lot more before it slows down.”
All of these regions, whether coastal or inland, have significant development that is uniquely vulnerable to flooding. The Florida coast contains thousands of homes on low-lying coastal land that is 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 flood when Helene passes. As intense hurricanes like Helene become more frequent, they expose these vulnerabilities.
“We’re entering this new normal of what we’re going to experience under climate change,” said Michelle Meyer, director of the Hazard Reduction and Recovery Center at Texas A&M University. “But secondly, what’s been going on for a long time is that we continue to build in really risky places, in ways that are also quite risky. So if we continue to add and add more homes in areas that are going to flood frequently, or add more homes on the coast without requiring greater mitigation, we’re going to see greater and greater dangers.”
Ayurella Horn-Muller contributed reporting to this article.
