Stacking soft drinks, snorkeling masks and kitchen supplies on high shelves, Jared Hunt of Keaton Beach prepared for Hurricane Helene to reach his small-town convenience store. He locked the door, sent his wife and son to stay with his sister in Ocala and rode out the storm in Perry.
“We came back to nothing,” Hunt said.
More than half a mile inland and eight feet above sea level, Keaton Beach Bums had flooded only twice since its construction in 1952. Each time, waters were a foot high inside. Hurricane Helene’s 14-foot storm surge topped the building’s roof.
With seven miles to the next closest corner store and 20 more to the supermarket, the town lost a key fixture.
“Growing up here, you always hear the worst of what's going to happen and then a lot of times you don't get that,” Hunt said. “This time we got the worst of it.”
New research suggests the intense flooding Hunt experienced is becoming more frequent along the nation’s coasts. The study found that once-a-century storm surge extremes — that is, levels with a 1% chance of happening in any given year —may now be twice as likely.
But storm surge is challenging to track in regions without tide gauges.
“There is also relatively higher uncertainty along other coastal regions (for example, Big Bend of Florida from Apalachicola to Cedar Keys) that have been impacted by major hurricanes but have no nearby operational tide gauge sites.” - Nature Climate Change study
What the researchers put in a parenthetical note, residents of Florida’s Big Bend felt in flooded roads and homes reduced to debris: The Big Bend faces high risks of storm-induced flooding but lacks long-term data to reliably estimate that risk.
Revising the numbers
Storm surge is often measured by National Oceanic and Atmospheric Administration tide gauges: futuristic-looking poles, panels and boxes installed near coastal areas. The gauges measure the normal coming and going of the tide, and, during storms, how high the water rises above the expected tide.
Researchers use a gauge’s previous data to determine how frequently different levels of storm surge happen. Typically, these calculations are based on a single gauge’s prior data. If a gauge didn’t record a big past event for any reason, its estimates may not reflect what actually happened.
Each instrument has, at a minimum, a main monitoring method and a backup. Data gaps can still happen because the gauge was installed recently, lost signal or was damaged in a storm.
In a study published this year, researchers attempted to fill these data gaps by using a statistical model to find patterns between data observed at nearby gauges.
“Things that are near one another tend to behave like each other,” said D.J. Rasmussen, a co-author of the study formerly affiliated with Princeton. “ You can use that relationship between those two gauges over many, many decades and get a reasonable understanding of what happens.”
The team found that this model provided a more accurate estimate of extreme storm surges than single-site analyses.
They concluded that the prior method may have underestimated the likelihood of extreme storm surge at 85% of the sites they analyzed nationwide.
For example, Hurricane Helene brought more than six feet of storm surge to St. Petersburg last fall, setting the city’s record. Traditional single-site estimates suggest this had a 0.07% chance of happening in any given year. The new study suggests the chance is more than six times higher. That’s in addition to sea level rise and land subsidence, which the study didn’t measure.
It’s important to note that the researchers compared their new data to prior academic studies. Comparisons to federal and state agency storm surge estimates are forthcoming.
The analysis also showed that storm surge extremes are becoming frequent in the Southeast. Researchers attribute the change to increasing coastal storm intensity since 1950, natural climate variability and human-caused climate change.
“Sea level rise has been front and center in terms of changing coastal hazards, and I think rightly so,” Rasmussen said, “but we show that [storm surge frequencies] are changing in ways that are not helpful.”
Those changes may be particularly significant along the Big Bend. Its concave coastline and shallow offshore waters can funnel storm surge inland, intensifying its impacts.
But stretches of the region lack tide gauges, making it difficult for the researchers to estimate how frequent extreme storm surges may be.
Red signifies a risk of storm surge greater than nine feet above ground during a category 1 storm. Orange - greater than six feet. Yellow - greater than three feet. Blue - less than three feet.
When sensors are scarce
The stretch of coastline between Apalachicola and Cedar Key flares neon red on flood risk maps, its low-lying beaches more like ramps than blockades to storm surge.
But on NOAA tide gauge maps, the same region is dark.
The 150-mile expanse between Apalachicola and Cedar Key has no instruments. Tampa Bay, for comparison, has four.
The Big Bend’s gap isn’t unique. The 200-mile stretch between Jacksonville Beach and Port St. Lucie, for example, only has one tide gauge. It also has a significantly lower risk of storm surge flooding, according to the National Hurricane Center.
NOAA has 207 operational tide gauge stations through its National Water Level Observation Network, the most recent of which was added in Alaska in 2017.
“If we had all of the money in the world, I think that we would have about 400 stations,” said Lorraine Heilman, who oversees the agency's tide gauges within the Center for Operational Oceanographic Products and Services.
The water level sensor and electronics of a tide gauge range considerably in cost, anywhere from $150,000 to $700,000 depending on if they're hardened to withstand extreme storms.
It costs approximately $14,000 to $16,000 annually to maintain a gauge, which accounts for things like emergency repairs and overhead equipment costs.
The agency’s 2024 evaluation of tide gauge priorities spans 93 pages, its rankings considering geographic gaps, marine navigation needs and coastal conditions, among other factors. It serves as a reference for the agency’s priorities, not a list of the regions next in line for a gauge.
Rankings list the Houston ship channel in Texas, Inner Bays of Indian River and the Upper St. Johns River in Florida as priorities in the southeast.
Florida’s Big Bend is shown as a “medium priority” coverage gap within the report.
NOAA operates additional water level stations with local stakeholders through a cost-sharing program known as the Physical Oceanographic Real Time System. “If someone in a specific area really would like a tide gauge, we can help them with that,” Heilman said.
That system and others bring the total of NOAA’s real-time water level stations nationwide to 314.
Separately, the U.S. Geological Survey and Florida’s Water Management Districts operate about a dozen permanent water level monitors near the Big Bend’s coast. The USGS and University of Florida each deploy additional, temporary gauges ahead of hurricanes.
The additional data are helpful, Rasmussen said, but imperfect.
“Not all of them have long records,” he said. “Some of those gauges are located in estuaries and rivers that are far away from the coastline, so you're getting influences from the geography that can impact your estimates.”
The multi-agency network of gauges still leaves a gap between the Suwannee River and the mouth of the Aucilla River. The gap spans 75 miles and includes more than a thousand residents, Keaton Beach’s Jared Hunt among them.
From data to decisions
Storm surge frequencies help inform how and where coastal residents build.
Flood protection methods such as elevating buildings or constructing breakaway walls are expensive, making it important for planners to balance costs and risks.
“We're not designing roads that are getting flooded by every medium tide,” said Katy Serafin, a coastal scientist at the University of Florida.
“ You can imagine if we've underpredicted the frequency of some event, say a 10-foot storm surge actually occurs every five years on average compared to every 100 years, you may have under-designed your structure.”
Federal, state and local agencies use a variety of methods to analyze flood risks. They consider single studies like Rasmussen’s in conjunction with other types of models, damage records and other climate and weather data when designing things like building codes.
Taylor County, for example, gave Jared Hunt the choice after his store was destroyed to build a new structure 17 feet in the air or set up shop in a “road ready” structure that could be trucked away at a moment’s notice.
Hunt chose the ground-level option.
He organized shelves, refrigerators and snacks into a semi trailer and reopened Keaton Beach Bums six months after the hurricane passed.
The store has grown to fill three trailers and a food truck, selling flamingo-printed shirts and dishing out mullet dip to neighbors and visitors alike.
A couple weeks ago, the gas company installed temporary tanks. “We did go back 50, 60 years, I do have to come pump your gas for you, but that’s alright,” Hunt said with a laugh, “We’d rather have that option than not have anything.”
“It's working and it's an option and people are happy to see us here, but it's not the forever option,” Hunt said.
Climate change is boosting coastal hazards globally through rising tides, more extreme storm surge and warming waters. The changing landscape has driven some waterfront residents to permanently relocate.
Alachua County expects its population to increase 8% by 2100 due to so-called “climate migrants” alone, according to the County’s 2024 Climate Vulnerability Assessment.
Alex Kolker, associate professor at the Louisiana University’s Marine Consortium, says tide gauges are particularly important for residents in sinking spots who face difficult decisions.
“People may decide to stay. They may decide to go,” he said. “As a scientist, I hope that they do that based on the best available information, and these gauges can provide that kind of information.”
Jared and Monica Hunt will stay.
They’ve both lived in the Big Bend their whole lives and are at home on the water. They’ll stick with the road-ready trailers for now and plan to build a wrought-iron structure with roll-up doors for a more permanent storefront once they get county approval.
If an extreme storm surge returns to their quiet coastal town again, “hopefully we don’t have to deal with that,” Hunt said, “but we’re going to be as ready for it as we can.”