During an event earlier this year before the start of the Atlantic hurricane season, National Weather Service Director Ken Graham talked about the biggest killer when it comes to tropical systems.
“Even the smallest storm – if it’s slow enough and big enough – is going to create catastrophic flooding and storm surge, right? There’s no such thing as ‘Hurricane Just-A.’ We gotta make sure the public pays attention.”
According to a 2014 study from the National Hurricane Center, just under half of all fatalities caused by tropical cyclones in the Atlantic between 1963 and 2012 were caused by storm surge – which is essentially the rise in sea level caused by a tropical system.
Because of that, learning as much as we can about the phenomenon can and will save lives. Atefeh Alipour is a doctoral student at Virginia Tech who has been researching storm surge characteristics.
“The storm surge is the most devastating phenomenon, national hazard along the U.S. coastline,” Alipour says. “It happens every year, every single year.”
A lot of the research, and forecasting, ahead of tropical systems and the resulting storm surge has historically focused on just how high the water will get. But Alipour and her fellow researchers stress that other factors are vital to consider.
“It is important how high water remains during a storm,” she says. “Like how long it remains.”
Alipour and her colleagues wanted to get a fuller picture of how a storm surge event evolves from beginning to end. To do that, they looked to the past.
“First of all, we extracted about 50,000 time series along the U.S. coastlines – about 700 locations – over the last two decades. And we wanted to focus on the extreme events, so we did pre-processing – filtering out the more than one-meter peak surge events,” Alipour says. “The other stuff we ended up having over a thousand time series and then we normalized them because we wanted to have representative curves that could be scalable to any other values. So, we normalized them – they are unitless – and then we grouped them. We group all the normalized time series to the eight distinct representative surge time series.”
Through a machine learning approach, the research group found eight unique storm surge patterns within that 20-year time frame that weren’t obvious when just looking at an individual tropical cyclone event. That included characteristics like a rapid surge before a gradual retreat or a storm surge event that remained elevated for a longer period of time.
Additionally, the data showed surprising variability based on where a storm would impact the contiguous United States – with some areas seemingly more prone to a certain type of storm surge characteristic compared to another.
“The more common patterns along the Gulf Coast rather than the Atlantic coast – we observed that the patterns that rise quickly are mostly prevalent in Gulf Coast areas,” Alipour says. “On the other hand, the patterns that can reach to the peak can be observed more frequently and more commonly in Atlantic coastlines.”
“The storm surge is the most devastating phenomenon, national hazard along the U.S. coastline. It happens every year, every single year.”
Alipour and her colleagues hope this information will be helpful to coastal communities and decision makers ahead of potentially devastating storm surge events.
“So, we wanted to help forecasting for more resilient coastal communities, right? These patterns are representative curves, they are scalable curves – they can be applicable for many different scenarios, storm scenarios,” she says. “Even preparing for evacuation, early hazard system and coastal management strategies could be improved by better knowledge and better understanding of storm surge evolution.”
This research is a first step, Alipour says – as there is still much to learn about the different variables that impact how storm surge will behave.
“I think the most important step moving forward is looking quantitatively at the factors that affect surge evolution and surge shape,” she says. “For example, we can say that during a hurricane that will approach to a specific area, we have this bathymetry, we have this coast shape and we have this background, this historical storm surge events – so which factor is the most important factor in this region. That could help us to predict and forecast better.”
You can read more about the research project here.
A very quiet Atlantic hurricane season so far...
As for the state of this year’s Atlantic hurricane season… it’s currently quiet and has been quiet – historically so.
Stephanie Zick is a tropical meteorology specialist at Virginia Tech, and she says depending on what metric you use, this year’s season has been at an all-time low in the Atlantic basin.
“This is another one that we use – it’s called ACE, or Accumulated Cyclone Energy. And by this metric, it is the least active season since the 1950s because that’s how far back this graphic goes,” she says.
Zick and some of her colleagues have discussed some of those other metrics as well, and while the data keeping at the time doesn’t match up to modern standards, this year’s season might just be the quietest since the early 1900s…
Why is that? Zick says there are two main factors that drive tropical cyclone development:
“So, the biggest things that control activity generally are ocean temperatures and vertical wind shear (that’s the change of wind speed or direction as you move up through the atmosphere). We have very warm ocean temperatures that would support tropical cyclones, but the vertical wind shear is very high. It just basically doesn’t allow them to form, even with those warm, sea-surface temperatures,” Zick says. “And the high vertical wind shear is because of the record El Nino.”
This time of year is considered the peak of the Atlantic hurricane season as well, which just makes the current situation even more interesting. The peak typically runs through the end of September, with the hurricane season overall stretching until November 30th.
El Nino isn’t going away anytime soon, so to get a tropical storm or hurricane through the rest of the season might have to involve development in areas that aren’t as common.
“I think the most likely route to get a hurricane this year is something in the Caribbean or Gulf. The Caribbean is a little rough though, too. The vertical wind shear is really strong in the Caribbean. But maybe in the Gulf – we’ve got very warm waters in the Gulf and the shear’s a little lower,” Zick says. “Or something in the subtropics. So, that can happen in the late season if you have what we call a mid-latitude cyclone and it moves off over warm waters in the Atlantic and transitions into a tropical cyclone.”
And this isn’t particularly good for large chunks of the U.S. that are still really dry from drought conditions seen this year.
“I mean, sure, we don’t want a Category 5 hurricane, but these storms actually do bring – it depends exactly you are, but I think in the Southeast U.S., it can be like 10% of the annual rainfall,” Zick says. “So that is a huge chunk of rain to not get.”
While the season as a whole may go down as a historically quiet one, Zick stresses that it’s still vital to be prepared for a hurricane. It only takes one to cause significant damage and havoc, so always having a preparedness kit and plan ready to go is essential.
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