When back-to-back hurricanes Helene and Milton slammed Florida, much of the damage they caused came from storm surge, the violent waves blown ashore in the path of hurricanes.
The National Hurricane Center has been issuing storm surge warnings since 2017, when Hurricane Irma threatened to make landfall on both coasts. Yet emergency officials still struggle to convey the risk to the public. At least nine people drowned in Pinellas County during Hurricane Helene.
WLRN environment editor Jenny Staletovich spoke to Cody Fritz, the head of the hurricane center’s storm surge team, about forecasting a hurricane's most lethal threat. What follows is an edited, shortened version of a longer interview that aired on WLRN.
STALETOVICH: So if we can start with Helene and Milton. How did you forecast and model them differently? Sort of, what were the challenges and what were the differences?
FRITZ: With Helene, yeah, it was, it was a big storm. It started out big. It remained big. It certainly intensified as it approached the coast, in comparison to Milton, which was a very small storm in its infancy, but a very, very strong storm overall. And then as it obviously traversed the Gulf of Mexico and made its way over to the Florida coast, it did weaken, but it also became bigger.
So it's not just that intensity of the hurricane. It's also what is the size of that storm. And that means how far out do those hurricane force and those tropical storm force winds reach? Because ultimately that's the force that's pushing the water towards the shore.
STALETOVICH: You know, I still tend to focus on, where’s it going to wind up. You know, that’s going to be the biggest threat. And clearly with Helene, it was, I think, about 100 miles offshore when it passed Tampa.
FRITZ: You're absolutely right. It was 100 miles offshore. And I think for many communities that live along the West Coast, they probably thought they were, in some ways, okay because the storm was well offshore. They were tracking that hurricane as it moved more north, northeast. But what you're tracking is ultimately just the center of the circulation, right? It doesn't even account for any of the hazards associated with that storm.
And so that's kind of where I come into play and try to communicate to you one of the specific hazards, being storm surge. Because ultimately storm surge is why we evacuate any coastal community. That has little to do with the wind and a lot more to do with storm surge. And the west coast of Florida is so vulnerable to storm surge. I cannot stress that enough. So even though Helene tracked west of the Tampa Bay area, its wind field was so large, in fact, that the tropical storm force winds, I believe, were in the 90th percentile, right? That means that there's only 10% of storms that have exceeded that size.
STALETOVICH: When you talk about that region, too, and that coastline, we've talked before about how surge is able to, I'm going to say hit it harder. That's probably not the technical phrase. But I mentioned my brother lives on Saint Pete Beach. He said that the water came in so quickly in his house, he sort of lost track of time. But he said it felt like under an hour. It went from just coming in to being so deep that he couldn't open the door. He had to crawl out a window. And so can you talk about that kind of that? Because I, that seems surprising to me. It was certainly surprising to him.
FRITZ: Yeah, so, you know, one of the reasons why we, we warn about storm surge is not just solely on how high the water can get. It's really the velocity at which that water can come in, right? So how fast that water can move. Because the combination of high water and fast moving water is very detrimental to life. It can cause death in many cases. And that's ultimately why we're telling you there's a danger of life-threatening storm surge. So, yeah, certainly in the case of, let's say, your brother, right. In St. Pete, when the storm surge comes in, it can rise several feet in a matter of minutes to hours.
So it's not just this slow creep up of water. It can come in very, very fast and then give you very little time to respond to that. That's why ultimately we're trying to promote those evacuation decisions when a storm surge warning is issued so people have the time to do what they need, get out of harm's way. Because when the water comes in, it's going to come in very, very quickly and you're going to have very little time to respond to it.
STALETOVICH: So sea level rise. I talked to a geologist last week who said that since 2000, sea levels in southwest Florida have risen about six inches. Is that accurate? And how are you factoring that into your models?
FRITZ: Yes, I mean, sea level rise is occurring. I mean, you can't deny it because you can observe that water levels have risen over the past several years and continue to rise as we move forward here. Can we account for those increases in sea level rise? Absolutely.
So whenever we are trying to forecast or predict storm surge, relative to the aspects that are associated with that hurricane, we also have to fundamentally know how high is the water at the current state. So we can initialize our models that we use to forecast storm surge. We can initialize those models with the current state, the current initial water level, and then use that as our base reference and then we can apply the various wind forcing characteristics of the hurricane on to that initial base state and from there, understand just what the significance of the storm surge would be, relatively speaking. Because ultimately it matters, right?
If you increase the water levels, you have a greater potential to not only increase the height of the water that's experienced at the coast, but also water can also penetrate further inland and you can inundate areas that may not have actually experienced storm surge before. And for those that live in vulnerable areas like the west coast of Florida, much of the areas along the Gulf Coast who will be experiencing sea level rise or have already experienced sea level rise, any hurricane that comes through can definitely make worse that storm surge hazard.
STALETOVICH: So we need to pay attention to sea level rise because safe ground may no longer be…
FRITZ: Yeah, I mean, absolutely. I think with or without sea level rise, I mean, if you live on the coast and if I can tell you anything about storm surge and these areas along the Gulf Coast, portions of the southeast coast and the East Coast, a lot of these areas are very vulnerable to storm surge.
And one of the bigger things that I've noticed, too, and we've talked about this, even with people's experiences of Hurricane Irma; Hurricane Irma didn't hit Miami. It went up making landfall on the West Coast and that's where some of the worst impacts were. If Hurricane Irma had hit Miami directly, it would be a completely different event.
And you can take a look at that from many different aspects of hurricanes where people's experiences are what they experience in that storm. But what they may have seen may not be the complete devastation of what that hurricane can do. And so I always caution people to not just use their experience in that hurricane, but understand that all hurricanes are different.
It very much depends on where those hurricanes make landfall. It very much depends how big and intense those hurricanes are. And if you live in a community along the coast, especially those on the west coast of Florida or the Gulf Coast or the southeast, and you are very vulnerable to storm surge, you can't just use your experiences in the past to guide your decision in the future, you know. It's our job to predict what's going to happen. And it's hopefully your job to respond to that prediction that we're making.
STALETOVICH: Well, it seems like having Helene and Milton come so close together, both in time and location, and behave so differently, there are lessons to be learned there.
FRITZ: There are absolutely lessons to be learned there. You have two hurricanes, very intense overall. But there are other characteristics about them that were different. Obviously, one was very big, remained big and continued to increase in intensity with time. One was small in the beginning, very intense, but weakened with time, but then became bigger. They made landfall in different locations, but many of the locations along the Florida West Coast were still impacted in some degree.
The specific thing about Tampa is that Milton made landfall south of the bay. And so a lot of the winds that you experienced were offshore. All the water went out of the bay rather than in. What's more interesting than that, as you could see, what can happen in a case where you had a storm still off the coast and made landfall north of you, then you got more of the onshore winds and therefore you got more of the storm surge.
If Milton had made landfall maybe 15 or 20 miles north of where it did, all that wind would have been onshore and it would blown all that water up the bay and you would have had a significant storm surge, probably in excess of about ten feet.
STALETOVICH: So going forward, are there things that you're looking at doing differently?
FRITZ: Our ultimate goal is obviously to continue to improve our modeling capabilities and trying to improve our ability to predict these storms. I think for storm surge specifically, though, our ability to better resolve the overall structure of a hurricane, because, again, it's all about the wind, where the wind is and where the wind is pushing water. That's it for storm surge. Where's the wind pushing water?
And if we can better resolve and understand the structure of the hurricane from a modeling point of view, we can better predict the overall amount of storm surge. And then from there, we can even better communicate those predictions to local officials, the public and the media, and have much more confidence in that prediction.
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