Since 2019, Florida has been in the crosshairs of seven different hurricanes. If the National Hurricane Center’s official forecast track and intensity for Helene verifies, this would make the storm the third major hurricane to make landfall in Florida in as many years.
Yet Helene’s become an outlier whose rapid progression from mere tropical disturbance to powerhouse storm has confirmed meteorologists’ fears: A fast-moving tropical system quickly intensifying over a relatively short distance has created one monstrous hurricane.
Brian McNoldy, a hurricane researcher with the University of Miami, said Helene has not taken the traditional route when it comes to formation. “Typically, you see these storms evolve over days and days and days,” McNoldy said. “Obviously, it has a cumulative effect building surge, but in this case we had a potential tropical cyclone only a couple days ago (on Tuesday) and a Category 4 hurricane by landfall.”
As a result, Helene had been able to strengthen into a massive storm, with 130-mph peak wind speeds and outer-band gusts stretching over 400 miles, which has meant far-reaching storm surge. By daybreak Friday, Helene had made landfall in Florida’s west coast and had quickly weakened into a tropical storm.
Every corner of the state of Florida has been covered by hurricane or tropical storm warnings and storm surge alerts are in effect along Florida’s Big Bend on the western coast, a testament to Helene’s enormity and widespread threat. Storm surge is the deadly and destructive wall of water that slams ashore from the intense hurricane-force winds blowing across the open ocean. The worst of the surging water — described by federal forecasters as “unsurvivable” — reached over 20 feet in coastal regions due to the generally northerly wind flow on the eastern side of Helene.
Surge is typically worse in the Big Bend part of coastal Florida, according to McNoldy, because “you’ve got all this onshore wind from the hurricane pushing water towards the shore, which has a coastline that is concave. There’s nowhere for the water to go other than onto land.”
As of Thursday, parts of St. James City near Fort Myers in Lee County, Fla., were inundated with nearly two feet of water over normally dry land. While this is only a fraction of the potential 20-foot surge that could overwhelm the Big Bend region of Florida, St. James City is more than 150 miles away from the center of Helene.
High tides also impact the storm surge, worsening the flood threat since water levels are already at or near their highest level of the twice daily cycle. Smaller storms, on the other hand, not only affect a smaller section of shoreline, but they have a finer needle to thread when it comes to coinciding with high or incoming tide.
Brian Tang, an associate professor of atmospheric sciences with the University of Albany, said the widespread impacts from Helene will be felt quite far from the coast.
“As we concentrate on the coastline, this storm will dump tremendous amounts of rain over southern Appalachia,” Tang said, adding that flash flooding and mudslides are possible all the way up to Tennessee. Several forecasters are predicting those areas could see some of the worst flooding in 100 years.
Warmer oceans
Stronger hurricanes typically produce higher storm surge and heavy rains and stronger hurricanes feed off warm ocean waters. According to Climate Central’s Ocean Shift Index, the near-record warmth of the Gulf of Mexico is 300 percent more likely because of our warming climate. And it’s more than just the sea surface temperatures that are warm — the index takes into account the depth of warm ocean water.
As hurricanes turn the ocean into a washing machine, the colder waters from below help cool the water temperatures at the surface. This can help slow strengthening or even help weaken a hurricane, but that is not the case with Helene. “If you have a lot of ocean heat content (warm water from surface to ocean floor), there’s not a lot of cool water there to be upwelled because the warm water runs deep. So in this case, we have a rather strong hurricane,” McNoldy said. And ocean heat content is running at a record high.
These warmer ocean temperatures help inject storms with even more moisture and help them to rapidly intensify right up until landfall. Helene strengthened even further Thursday night, to a Category 4 storm, just hours before it’s forecast to make landfall late tonight. According to Tang, “this rapid intensification trend is increasing, largely due to climate change.”
Meteorologist Chris Gloninger is a senior scientist in climate and risk communication at the Woods Hole Group. Follow him at @ChrisGloninger.