The future of hurricanes

Tom Knutson has been thinking about weather, in general — and hurricanes, in particular — along with the stampede of stimuli that form them for many years. It probably started in his boyhood in the southern Virginia mountains, a long way from the Atlantic basin where, this year, the named storms have just kept coming.

So far, four have been major hurricanes in a season that won't formally conclude until Nov. 30.

He thought about them right through his undergraduate days at the University of Virginia in Charlottesville, his post-graduate doctoral work in Wisconsin, where they don't have any hurricanes, and now for years as a senior scientist for the National Oceanic and Atmospheric Administration. There, he thinks about them in Princeton, New Jersey, in NOAA's Geophysical Fluid Dynamics Laboratory.

Knutson spends a lot of time wondering — and getting asked — a question urgent for a lot of Floridians who may be weighing the merits of clinging to a Sunshine State subject to such seasonal storm violence: Do demonstrably warmer oceans coupled with higher sea levels mean hurricanes will be both more frequent and more intense from now on?

The data established so far doesn't necessarily suggest a greater frequency of storms caused by climate change, he said — that's the good news.

"We have some confidence in our (predicted) U.S. landfall numbers — the trend is flat over a century, and so is the number of major hurricane landfalls."

For that matter, several climate scientists agree, seeming novelties such as hurricanes that form in the western Gulf of Mexico, like Helene and Milton, are not in themselves indicative of a new pattern.

Instead, says Joanne Muller, a professor in the Department of Marine & Earth Sciences at Florida Gulf Coast University's Water School with a doctorate in paleoclimatology, that may be down to luck, or bad luck as some define it.

She offered answers to Florida Weekly questions by email from a research vessel off Guam in the South Pacific Ocean, hunting new data.

"Many studies indicate that there has been no significant change in hurricane frequency in the Atlantic since 1900, and some studies indicate decreasing global frequency of tropical cyclones," she said.

If that's a relief, it's incomplete.

"The thing we have most confidence in," Knutson added of NOAA's research: "All hurricanes are coming in on a higher background sea level, so the storm surge is worse, and we think hurricanes are getting rainier — it's going on with global warming, precipitation is more extreme."

So, hurricanes are going to be water threats.

As for the wind speed of future storms, "there's some uncertainty, but models generally indicated an increase, so storms will get more intense," Knutson said. "But the magnitude is only about 3% — it's a range of minus 1% to 10% in the Atlantic basin."

As Muller put it: "The models do point towards an increase in storm strength and rapid intensification in the future, along with increased precipitation. The observational records also indicate rapid intensification and increased precipitation in tropical cyclones (hurricanes)."

Unfortunately, future storms may be inclined to sit on us.

"Some studies indicate a slower translation speed, that has the ability to increase both storm surge and rainfall rates," Muller explained. "Higher amounts of water vapor in the atmosphere may contribute to slower decay over land."

That's a lot to think about, but Knutson probably wasn't thinking about it, at least not directly and personally, when Hurricane Helene walloped the southeastern United States in late September, exactly 24 months after Hurricane Ian eviscerated Southwest Florida. Helene made landfall in the Big Bend as a category 4 storm on the Saffir-Simpson scale, with sustained winds as high as 156 miles per hour.

Then Helene did something unprecedented, not only driving into the southern mountains and, with storm surges and floods, killing more people than any hurricane since Katrina hit New Orleans 19 years ago, but the storm seemed to come looking for Knutson himself.

He and his family keep a little place in the Virginia mountains where he grew up, he said — and where he had to speak to a reporter on a cell phone with a tentative connection dependent on a distant tower because Helene had chased him down in the mountains, located the climate scientist's homestead retreat, and knocked over his much more dependable satellite dish.

"It was nothing compared to what happened to others," he said. "But I didn't expect it."

The data at this time, however, does not indicate that Knutson or his colleagues at NOAA have been specifically targeted by hurricanes.

The long view

Other scientists, echoing Knutson and Muller, caution against drawing conclusions about weather changes in Florida — or anywhere — just from the patterns of a few years or decades, or even more than a century.

"We have a historical record well delineated going back to 1851," noted Ryan Truchelut, who holds an undergraduate degree in geosciences from Princeton University (he graduated summa cum laude) and a doctorate from Florida State University's Department of Earth, Ocean and Atmospheric Sciences. He co-founded his company, Weather- Tiger, in 2013 to offer "both operational forecasting and research science" and provide "mission-critical forecast science and consulting (to) agricultural markets," among others, publishing a hurricane newsletter and Substack, and appearing regularly to forecast in prominent media such as USA Today.

"That's 170 years of data, but not many people lived in South Florida then, so we really only trust a data set going back to 1900 for catching and observing every landfall," he said. "In that time, there have been periods of higher activity and periods of lower activity. Right now, there's not a long-term trend in the number of hurricanes that make landfall in the state doing back 125 years. It's basically flat."

Consequently, what's going to happen going forward isn't entirely clear, in spite of our increasingly significant, data-based knowledge about climate change and the so-called steering factors that cause and shape hurricanes in any period of time.

The "luck" part of the equation may look like this: "There are periods. In the 1940s and '50s, Florida was slammed over and over again, with South Florida the target. Then there was period when not all that much was going on. In the last eight years, the Gulf coast has been the target, with an incredible profusion of landfall events. There were two major landfalls in the state in 2004 and 2005 (Truchelut, who grew up in Orlando, went through Hurricane Charley when the eye passed over him). But between Wilma in October 2005 and Hermine in September 2016, we had tropical storms but no major hurricanes."

What conclusion can be drawn from that fact?

"Peoples' memories tend to be short and focused on what's happened in the immediate past," he said.

Understandably. The immediate past was no fun, in terms of hurricanes.

"But as a hurricane climatologist, I'm trying to take the longer view. The longer view is this, more or less: We don't have the evidence to say, yes, there will be more hurricanes going forward. It's semi-random. I wouldn't be surprised if there has been a change in steering patterns (winds and currents) due to climate change, but it's too early to know that."

One thing clear to Truchelut, a fact about which there can be no dispute: "Sea levels have risen. We've had at least a foot of sea level rise in 70 or 80 years. That will make storm surge worse, and coastal flooding will get further inland. So: whatever is making landfall will have a higher impact."

Another disturbing fact, he said: "Oceanic temperatures have changed quite a bit. For the past two years, the Gulf has been at record levels, at the peak of (hurricane) season. It's been in the upper 80s as opposed to the lower to mid-80s in, say, September."

That's not good for the future.

"Here's the takeaway from this, and research supports it," Truchelut concluded: "There's no way you can have water temperatures in the Gulf in the upper 80s this randomly — it's way beyond the natural variability of a pre-industrial climate. We've unnaturally changed the Gulf."

As a result, the storms we see in the coming years, though not necessarily more frequent, may be more savage.

"We always have a choice in how we're going to be resilient," Truchelut said. "It's a question of, how can we live with the land and the sea? Hurricanes are a natural process, as old as time itself. How is the threat profile going to change?"

But in determining that, he said, "I can't emphasize enough: We should not draw long-term conclusions from short-term apparent trends." ¦

In the KNOW

To learn more about the scientists interviewed in this :

· Tom Knutson's homepage: www.gfdl.noaa.gov/tom-knutson-homepage

· Ryan Truchelut's homepage: weathertiger.com/about/who-we-are