I am a product of the Crescent City. Most of everything that I love can be tied back to my hometown — spicy food, great music, and hurricanes. Especially hurricanes.
In the springtime, I remember looking up as giant river barges floated down the Mississippi River above my parents’ home. I spent hours high atop the levees that cradled the mighty Mississippi. To a young flat lander, those levees felt like mountains of the swampland. In a city whose average elevation is only one to two feet below sea level, they were; a 20–25 ft mound of dirt was the farthest and highest I’d ever been from the water.
It’s difficult to grow up in New Orleans and not have an innate fascination with hurricanes. Each Saturday morning, on my way to tennis lessons at City Park, I would cross the Orleans Avenue Canal along Harrison Avenue and marvel at the curtain floodwalls that veiled any glimpse of the surrounding sea from the Big Easy castle. What would happen if a Category 3 hit?
Years later, I found out.
The scope, the damage, the absolute totality was incomprehensible. In all of the fanciful scenarios I drew up as a hurricane obsessed child nothing came close to what I saw with my own eyes. It’s easy to dismiss what happened in New Orleans as an engineering failure but what happened in coastal Mississippi wasn’t. Nearly 200 people died there, mostly from storm surge. It was something more.
Storm surge was always keenly interesting to me, but in the context of the hurricane and hurricane forecasts. That is, as a budding scientist, I wanted to find a way to improve the forecast so we could better predict the Cat 3s, 4s, and 5s that might flood my city. During the year of Katrina, I was in graduate school in the midst of doing just that. But in the months leading up to Katrina, a small but intense and largely forgotten Florida hurricane came along that forever changed my world view of storm surge.
Hurricane Dennis made landfall about 20 miles east of Pensacola in the western Florida panhandle on July 10, 2005. As the the Category 3 hurricane moved across Santa Rosa Island, a 6–7 foot storm surge flooded nearby beach communities. This was forecast and expected. What wasn’t expected was the scene at Panacea, Florida, 150 miles east of where Dennis came ashore, where, at the time of landfall, there was no hurricane warning.
Nearly 9 feet of water poured into Angelo’s Seafood Restaurant on Ochlockonee Bay, where winds at the time barely gusted to tropical storm strength. How could storm surge, seawater flooding driven ashore by strong onshore winds, be higher where winds were 80–90 mph weaker? As it turned out, there was more to storm surge than just the Category.
That one forgotten hurricane changed not only the trajectory of my career but more importantly launched over a decade of change to how we forecast and communicate storm surge. Since 2005 we’ve vastly improved our storm surge modeling capabilities so that sneaky surges far away won’t surprise us in the future. In 2010 we officially removed storm surge from the Saffir-Simpson Hurricane Wind Scale. And for this hurricane season the National Hurricane Center (NHC) announced the addition of two new products aimed at communicating life-threatening storm surge information to the public.
Weather communications is a tricky business. I learned this quickly during my first few years in broadcast media. Information that seems so straightforward to us meteorologists isn’t always so obvious to the general public. As the lead scientist on the development of these new storm surge products during my time at the National Hurricane Center, I thought it would be worthwhile to take a closer look at them, what they [actually] mean, and how to avoid any pitfalls as a weather communicator.
Storm surge isn’t just a coastal problem. For as long as we’ve issued hurricane forecasts, storm surge has been characterized as a line along the coast from Point A to Point B.
Storm surge, however, doesn’t stop at the beach. In some cases, it can surge 30 or 40 miles inland. That’s where the new NHC Potential Storm Surge Flooding Map comes in.
The beauty of this new product is that is clearly shows the vulnerability and exposure of even inland locations to storm surge from a landfalling tropical storm or hurricane.
As elegant as this map is, though, it can be easily misinterpreted.
For example, if your area isn’t colored, does it mean you won’t be asked to evacuate? No. Hurricane evacuation is a completely separate business and the Potential Storm Surge Flooding Map should never be used by the general public for evacuation decision making. Even if it shows your area dry, you could live on a high spot surrounded by areas at risk for serious flooding (see parts of Galveston Island above). For your own safety, your local officials may decide to include you in a hurricane evacuation order. If bridges to your island community are washed out, you’ll be cut off from emergency services. That isn’t a safe place for you and your family in the days and weeks after a hurricane. So regardless of what the map shows, always check with your local officials first and heed their advice.
Another potential area of confusion is what this map represents. The Potential Storm Surge Flooding Map is not intended to show the areas where we expect storm surge flooding to occur. In that sense, it’s not a flood forecast map. Instead, the potential flood map is based on thousands of storm scenarios that give a reasonable worst-case flood level for each location on the map. Take for example the areas painted in red. Not all of these areas are expected to see greater than 9 feet of flooding but if you live inside a red zone, the potential exists for greater than 9 feet of flooding at your location. Even if the reasonable worst case doesn’t materialize, it’s what you should prepare for.
Storm surge is incredibly complicated and even the smallest changes to a forecast have huge (huge) ramifications on when, where, and how high the flooding will be. To accurately forecast storm surge means first being able to accurately forecast every aspect of a hurricane (size, intensity, speed, track) plus knowing a thing or two about hydrodynamic modeling, or how the ocean works. If you thought weather forecasts were humbling, try storm surge forecasting. If we were to attempt to forecast exactly where the water will go based on a single hurricane forecast, or even just a handful of hurricane forecast scenarios, our storm surge forecasts would yo-yo with every new forecast cycle. Can you imagine seeing a forecast of no flooding for your location a few days before landfall, then waking up the morning before landfall to expected flooding of greater than 9 feet? That would lead to mass panic and confusion.
You should prepare for a reasonable worst case scenario because, albeit infrequent, storm surge is an extreme event. Water moving at only 4 mph has the same damage potential as the winds of a Category 3 hurricane. 90% of hurricane related deaths are from water. Storm surge is the deadliest hazard of a hurricane. I can go on but needless to say a few feet of ocean water in your neighborhood is a big, life-threatening deal.
Which brings us to the second new storm surge product from the National Hurricane Center — the storm surge watch/warning graphic.
It’s experimental this season, but don’t let that throw you; you’ll see the watch/warning but it means the government is still warming the engine. They may need to fine tune a few things after the season, but if all goes well beginning next hurricane season the storm surge watch/warning will graduate from a single graphic to part of the official suite of watches and warnings from the National Weather Service.
The storm surge warning is the big brother to the inundation graphic. If the potential exists for life-threatening storm surge from Hurricane X, big brother steps in to warn the public about it. But why a separate storm surge warning? Doesn’t the hurricane warning already cover this? Actually, it doesn’t. The hurricane warning only covers the wind. A watch or warning from the National Weather Service is meant to signal the potential for dangerous or life-threatening weather. As it stands now, we have no signal for dangerous or life threatening storm surge. And as Hurricane Dennis showed us in 2005, dangerous storm surge can extend outside of the hurricane warning.
And what about the storm surge threat inside those levees that piqued my early curiosity in hurricanes? Well the science isn’t there just yet to tell us exactly where the water could spill over or if the storm barriers might be compromised. If you live in these vulnerable areas like New Orleans, you might feel left out, but it’s done in your best interest. Consult your local officials during any storm threat and, regardless of the Category, if you’re ordered to evacuate, please do so. There are low grade hurricanes and even strong tropical storms that can cause problems for our most hardened levee systems. As someone who developed the computer models we use to forecast storm surge for this country, trust me when I say this.
Katrina reminded us that, even in 21st century America, thousands can die in a hurricane, primarily from storm surge. Four of the five deadliest natural disasters in U.S. history were water related, and three of those five were storm surge related, including the deadliest of them all — the Great 1900 Galveston Hurricane. 22 million Americans now live in areas vulnerable to storm surge flooding. Our most vital ports, key oil and gas production facilities, and even some nuclear facilities sit in our most surge-prone areas. It’s not good enough to get a forecast right. A perfect forecast gives us a weather touchdown but great communication of that forecast wins us the game. So take a few minutes to familiarize yourself with these new storm surge products and how to use them for this hurricane season. It’ll give you the view from high atop the levee, where water is no longer second class citizen but a very real and ever-present part of our growing coastal community.