Hurricane Ian is now the deadliest hurricane in the continental United States since Hurricane Katrina in 2005. It made landfall on September 28 along Florida’s gulf coast at Category 4 strength, with sustained winds of 155 mph driving a storm surge as high as 18 feet, flinging boats and sweeping homes off foundations.

As of Friday morning, officials report that at least 101 people are dead from the storm, 89 of them in Florida — 45 in Lee County, which includes Fort Myers and Cape Coral. More than 60 percent of the deaths were due to drowning.

“That’s something I’ve never seen in my 38 years in public safety in Lee County,” said Cecil Pendergrass, Lee County Commission chair, during an October 2 press conference.

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It’s an extraordinary tally, one that bucks a decades-long trend of declining disaster casualties. Even as climate change has worsened rainfall and storm surges during hurricanes, and even as populations have grown in coastal areas, such storms have killed fewer people in recent years. Florida in particular has a long history preparing for and rebuilding from hurricanes, and deadly storms are increasingly rare.

“I think we, as Floridians especially, we know that we are always going to have hurricanes,” said Abdul-Akeem Sadiq, a professor of public administration at the University of Central Florida who studies disaster response and recovery. “We cannot let our guard down.”

Yet for Florida, Ian now has the highest death toll of any hurricane to hit the state since 1935. The question, then, is why Hurricane Ian proved to be such an outlier.

The factors behind Hurricane Ian’s death toll

Hurricane Ian’s deadly course highlights that while fewer people are dying from hurricanes in general, it’s a trend that anyone can take for granted. Driving down disaster casualties requires proper planning and a robust response. Failure on either front means more people will die.

The storm itself was unusual

Hurricane Ian followed a route less traveled, as it spooled up in the Caribbean and climbed north into the Gulf of Mexico before hooking east toward Florida. While the state does experience regular hurricanes, not every part gets hit with the same frequency. The last time a Category 4 hurricane hit Florida’s west coast was Hurricane Charley in 2004.

Predicting Hurricane Ian proved especially tricky

Meteorologists have dramatically improved their ability to see where a hurricane is heading, sometimes 72 hours or more ahead. Twenty years ago, such a forecast could only be issued 24 hours in advance. But Ian still proved confounding.

“Ian was approaching the coast at an oblique angle, so that small changes in the hurricane’s projected track made a large difference in where the storm would hit,” said Jeff Masters, a former hurricane scientist at NOAA who now writes about extreme weather and climate change, in an email.

In addition, Hurricane Ian underwent rapid intensification, a phenomenon where a hurricane gains more than 35 mph in wind speed. For meteorologists, this remains a difficult trait to anticipate, so a storm whose path is known could still land with surprising strength. And Ian rapidly intensified twice over, surging from 75 mph winds to 155 mph in 48 hours.

People were confused about how to parse the forecast

Lee County, home to more than 750,000 people, only ordered an evacuation 24 hours ahead of Hurricane Ian’s landfall. Pendergrass, the Lee County Commission chair, said that they didn’t order residents to leave sooner because the county was outside of the storm’s projected “cone” three days earlier.

National Hurricane Center

But the forecast maps of Hurricane Ian from the National Hurricane Center warn that the cone doesn’t show the full size of the storm and that dangerous conditions can still occur beyond its boundaries.

“It is the storm surge watches and warnings that people should be paying attention to, not the whether or not the cone is over them,” Masters said. Storm surge, where winds push a wall of seawater inland, is often the deadliest aspect of a hurricane.

National Hurricane Center

And given Florida’s long history with hurricanes, officials should have understood the limits of predictions and potential for destruction beyond what’s shown, according to Masters. “Understanding forecast uncertainty is something every emergency manager should be an expert on,” he said.

Without a formal evacuation order, officials didn’t muster the resources to get people away from the coast in time. That’s particularly critical for low-income residents and older adults who may not have the means to leave or a place to shelter away from their homes. And many residents who could have left on their own took the lack of a mandatory evacuation as a signal that the storm wasn’t going to be that dangerous and stayed.

The population in vulnerable coastal areas has grown

Since 2010, Florida’s population has swelled by nearly 3 million people, with coastal areas seeing some of the largest increases. Lee County grew by more than 167,000 people during this period. Many of the newer residents are older adults, particularly retirees, who are often more vulnerable during disasters.

“We had a lot of people move here in the last five years that have never been through a hurricane,” Pendergrass said. That may have led them to underestimate the risk.

More people also means more homes, cars, power lines, and roads that are vulnerable during a hurricane, increasing the financial costs of the storm.

Complacency had set in

Though hurricanes don’t always get as strong as Ian did, they are still a regular occurrence in the southeastern US. Hurricane Irma, the last Category 4 storm to make landfall in Florida, led to an evacuation of an unprecedented 6.8 million Floridians.

“We have to always remember that this could happen again and we should be ready for the next one,” Sadiq said.

Only 10 people in Florida were killed directly by Irma. The lower severity and lesser damage from Irma and other storms in recent memory may have misled people into thinking Ian wasn’t all that dangerous.

“We’ve actually been in the cone” during previous storms, Pendergrass said. “People get callous to that.”

In addition, there wasn’t much effort made to interrogate past hurricane forecasts and to educate the public about how to respond to uncertainties, particularly when a storm takes a different course than what was predicted, according to Sadiq. It can also be hard to appreciate how much planning and evacuations saved lives, even if they may be an overreaction in some cases.

“The next time a prediction like that is made, people are less likely to heed that warning,” Sadiq said.

Hurricane Ian’s full impact is still growing

Though the winds have died down and the waters have receded, Hurricane Ian is still casting a long shadow. Past hurricanes have shown that the greatest dangers don’t always come from the storm itself but during the recovery, as people grapple with power outages, poor sanitation, no shelter, injuries, and a lack of medical care. These deaths are the hardest to track. It’s also tricky to separate which deaths are “natural” from the storm and which ones stem from human failures to adequately prepare and respond.

With Hurricane Irma, for example, there were 84 indirect deaths in the aftermath of the storm, 77 of which were in Florida.

Hurricane Maria in 2017 is an even starker case. That Category 5 storm knocked out Puerto Rico’s power grid for months, creating the largest blackout in US history. That led to more than 3,000 deaths, most after the hurricane had long dissipated. Similarly, Hurricane Katrina killed around 1,800 people, most during the flooding and societal breakdown after the storm itself passed.

“If we use the Hurricane Maria model with Ian, there are some deaths that haven’t even happened yet,” Samantha Montano, an assistant professor of emergency management at the Massachusetts Maritime Academy, said in an email.

Ricardo Arduengo/AFP via Getty Images

More recently, Hurricane Fiona made landfall in Puerto Rico as a relatively weak Category 1 hurricane but still caused a blackout across the whole island. As of Friday morning, more than two weeks later, 79,000 utility customers in Puerto Rico still don’t have power.

And deaths are only the most severe outcome from disasters. Many people who survive hurricanes can still have lasting health problems from injuries, illness, and the stress of dealing with the storm.

“One aspect that doesn’t typically get much attention is the psychological impact of disasters,” Sadiq said.

The survivors of a storm have to handle the grief of losing loved ones and their possessions. Many suffer conditions like post-traumatic stress disorder or experience a sense of dislocation, particularly if they’ve had to move permanently. Without treatment, the mental health burden from Hurricane Ian will likely grow and impair the effort to rebuild and restore lives.

The good news is that the overall downward trend in deaths from hurricanes shows that many casualties can still fall further.

“In my opinion, the United States has the knowledge, resources, and technology to prevent this kind of high hurricane death toll,” Montano said.