Hurricane Dorian delivered a minor blow to much of Florida this week after spending a deadly day and a half over the northern Bahamas. Dorian is the fifth Category Five storm in the Atlantic in four years—after Matthew, Irma, Maria, and Michael. Climate researchers now see a trend of hurricanes stalling in coastal areas like Dorian.
Other recent examples of hurricanes stalling and dumping large amounts of rain over a small area include Hurricane Harvey in 2017 and Hurricane Florence in 2018. The longer a hurricane stalls, the more rain it pours on that area.
While many climate experts cannot draw a direct link between stalling hurricanes and global warming, they do say it fits with some of the changes to large scale hemispheric weather patterns that could be driven by global warming. But proving a direct link requires studying many more intense hurricanes over many years.
Dr. Andrea Dutton is a professor of geology at the University of Wisconsin, studies climate change to predict the future of sea level rise. Bob Berwyn is a reporter for Inside Climate News. Both were guests on The Florida Roundup.
An excerpt follows.
The Florida Roundup: As the science is getting collected from Dorian, what strikes you first of all about the speed of the storm or the lack of it?
BERWYN: I did, in relation to Dorian, speak with several climate researchers, who have in recent papers, detected a trend of more hurricane stalls by the definitions that they used which involved proximity to the coast in forward speed – translation they call it. They were very careful to say that they can't see it or identify a direct link to global warming, but that the trend of more hurricanes stalling in coastal areas over the last 50 years is pretty clear to them.
Again, they're not saying that you know we can say 100 percent that this is caused by global warming but, they are saying that it does fit with some of the changes to large scale hemispheric weather patterns that could be driven by global warming shifts in the in the Bermuda high, changes to the jet stream and westerly winds. And again, you don't know direct link. It's really hard as Andrea said to pick out a fingerprint signal out of all the noise. But we also have to act on what we do know sometimes.
As scientists and researchers look to ascertain whether warming oceans are slowing down the storms, certainly the stalling of the storm that people in the Bahamas experienced was absolutely devastating. How long it remained stationary and how slowly it moved over those populations. I'd like to get your thoughts about that as well.
DUTTON: It's just terrifying. It's bad enough that there was a Category 5 hurricane clocking in with sustained winds of 185 miles per hour. But unlike Hurricane Michael, which tore across the panhandle move very quickly and we all saw the devastation that was left behind that. This hurricane just parked itself and was there for I think more than 24 hours.
And that's really scary. We were just talking about increases in rainfall. That will happen anyway with a warmer atmosphere. But if these hurricanes are moving slower or stalling and not moving, there are periods of time when it was technically classified as stationary not even moving at all. That will really increase these total rainfall amounts as it just sits there and rains. We all remember seeing that with Hurricane Harvey too.
So, it's one thing to build a structure that might withstand Category 5 winds but then you have to ask yourself the next question can it withstand that for 24 hours or longer -- which is really a whole different ballgame.
People that have loved living on coastlines for many years are looking at the prospect of more intense storms. They're talking about picking up stakes. Increasingly we hear that from people here in Florida and it's not just a phenomenon unique to Florida. Right?
BERWYN: Absolutely not. I've spoken with actually with a climate researcher who lived in Tucson, Arizona. He was at the university there for many, many years and recently moved to Michigan and when I interviewed him first time after his move he said one of the reasons he's moving is heat waves and water shortages and. He called himself only half joking – a climate refugee.
We hear that term increasingly and I think that's worrisome when you look at the future viability of Florida. Andrea Dutton you've moved to Wisconsin but you've spent a lot of years here in Florida. Did you move to Wisconsin because of this? Are you a climate refugee or was it some other reason that prompted your move to the Midwest?
DUTTON: That's a great question and obviously the big move like that there are a lot of factors to consider but climate change was definitely one of them. I spend 24/7 thinking about this, researching it, talking to the public about it. I've looked at those graphs of what it's going to be like in 10 years. And that was definitely one of the reasons. So, I would yes again half-jokingly call myself a half climate migrant…
One point I made to an audience I spoke to in Miami recently is even if you just look at heat right the most the most direct effect of climate change and how that is changing and the number of days you have say over 90 degrees. In Miami the number of days over 90 degrees has increased by about 73 days since 1970. It started about 40 days a year now it's well over 100 days a year. And by the year 2030 we expect danger days where we have a heat index of 105 to be at about 126 days a year in Miami. That's one in three days. Imagine trying to do any work outside right in when the heat index of 105.
Here in Jacksonville people are saying, ‘well it's hurricane season.’ What's the big deal? But as you look at these data points over many decades, yes, we're always going to have a certain number of hurricanes but we're very concerned about the escalating intensity of these hurricanes. Correct?
BERWYN: My partial answer to that would be as number one there is a few different ways to measure intensity -- the strength of the wind speeds, whatever it is on the Saffir-Simpson scale. There’s also rainfall which is obviously one of the most dangerous factors associated with hurricanes.
And in that particular metric have been a number of studies the last few years on Florence on Harvey, that have made a direct attributable link to the amount of rain that comes from one particular storm. It's called attribution climate science. And that's pretty good science. That's one metric we could probably say pretty clearly as it has already been discussed here. You know that global warming is fueling storms with more rainfall.
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