After a year of record coastal flooding, eastern North Carolina may feel a slight reprieve from high-tide flooding days between now and April 2025.
The National Oceanic and Atmospheric Administration’s National Ocean Service last week released its 2024-25 Annual High-Tide Flooding Outlook, which projects slightly fewer of these flooding days through spring 2025 than last year. That’s because El Niño conditions are transitioning to La Niña conditions, and these two opposing climate patterns in the Pacific can affect weather worldwide.
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“Bottom line: Over the past year, we’ve seen record coastal flooding, or high-tide flooding, along our coastlines,” Nicole LeBoeuf, National Ocean Service director, during the Aug. 6 online news briefing, said. “When the ocean runs hot, sea levels run high, and we see that playing out in our coastal flooding data.”
The outlook recaps high-tide flooding events from May 2023 to April of this year at 97 NOAA tide gauges along the U.S. coast, and it projects what to expect at these locations through April 2025.
High-tide flooding, which is sometimes called nuisance or sunny-day flooding, happens when tides reach anywhere from 1 to 2 feet above the daily average high tide, and cover what is typically dry land along the coast. “As sea levels continue to rise, high-tide flooding occurs more frequently, even without severe weather,” she said.
For the 2023-24 season, coastal communities in the United States experienced seven to eight flood days, LeBoeuf said. In 2023, 34 locations broke or tied their records for flood days, which she called “a dramatic increase” from the previous year.
Hot ocean temperatures led to the highest levels of sea level measurement on record. There were 44 NOAA tide gauge locations, mostly on the East Coast, that broke or tied their previously recorded sea levels to date. This means “we got an additional 6 inches of sea level rise and five median coastal flood days annually compared to the year 2000, roughly a 200% increase,” LeBoeuf said.
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The recurring climate pattern called El Niño contributed to the record-breaking 2023-24 observations.
“El Niño typically raises ocean temperatures and can result in more frequent and intense storms hitting the coastlines, especially along the East Coast, where we saw many records break this past year,” she said. “With sea level rise and high-tide flooding increasing, El Niño simply makes things worse for coastal communities, home to almost 40% of the U.S. population.”
Because high-tide flooding can degrade infrastructure, damage property and disrupt coastal ecosystems and people’s daily lives, NOAA works to help communities predict this kind of flooding and its potential impacts, she said.
NOAA maintains the tide gauges across the U.S. and its territories that make up the National Water Level Observation Network. Some of the gauges have been recording water-level data for more than 150 years. Through this network, “NOAA monitors the unrelenting creep of sea level rise and the rapid increase of high-tide flooding,” LeBoeuf said.
The outlook brings together data about high-tide flooding events between May 2023 and April 2024. That time frame is used to “account for increased sea levels in the fall and increased stormy weather during winter months, so that we can most effectively predict the year ahead,” she continued.
There are four National Water Level Observation Network stations on the North Carolina coast. According to the annual outlook, Duck experienced 22 high-tide flood days between May 2022 and April 2023 compared to 13 the year prior. Oregon Inlet Marina encountered seven days, up two from the previous year’s five. High-tide flood days at the Duke University Marine Lab at Pivers Island in Beaufort increased from six to 11. At the Wilmington tide gauge, high-tide flood days increased from two to three.
“Almost every location we measure between New York and Georgia broke their sea level and flood-day records in 2023. It’s like El Niño had the US East Coast in its Bullseye,” she said.
In the coming year, NOAA projects that the country’s coastal communities will see a median range of four to eight high-tide flooding days between May of this year and next April, which she said is slightly down from last year “as we move away from El Niño and into La Niña conditions.”
The outlook projects that for Duck, there will be nine to 15 high-tide flood days, four to seven at Oregon Inlet Marina, four to six at Duke University Marine Lab in Beaufort, and two to six in Wilmington.
NOAA’s National Ocean Service researchers predicted that this year’s Atlantic hurricane season will increase the chance of significant flooding in some places, particularly along the Atlantic and Gulf coasts.
Hurricane predictions are not directly factored into NOAA’s high-tide flooding outlooks, but the product “can provide situational awareness regarding baseline flooding that can compound the impacts from real-time weather events like hurricanes and tropical storms” she said. “Events like hurricanes get a lot of attention, but high-tide flooding is one of the most tangible impacts of long-term sea level rise, reminding us that while we brace for impact today, the United States must also plan for a wetter future.”
NOAA scientists project that communities across the nation will experience an average of 45 to 85 high-tide flood days per year by 2050, which means that “every four to eight days, Americans along our coast will face disruptive and damaging seawater inundation regardless of the weather at the time.”
The federal agency also produces a Monthly High Tide Flooding Outlook to provide flooding likelihoods each day of the year, up to a year in advance, offering windows of time where there’s increased flood risks.
“Together, these outlooks complement one another with information across time scales to protect lives, ecosystems and economies as towns, states, tribes and businesses are faced with increased coastal flooding,” LeBoeuf said.
Coastal Ecologist Dr. Christine Voss, who recently retired from University of North Carolina Institute of Marine Sciences based in Morehead City, in response for comments about this high-tide outlook, explained that the trends in rising sea levels and the acceleration of global, regional and local water levels are sustained, and the data are clear.
“If one examines the entirety of the data, there is some annual variation, yet the ‘big picture’ is unchanged. In its reports, including this one, NOAA makes clear that the Southeast US region, including coastal NC, is experiencing more high-tide flooding due to global sea-level rise, land subsidence, and regional oceanographic effects — compared to 2000 and the previous century,” she said in an email.
NOAA’s Aug. 6 article suggests that the expected development of La Niña is likely the reason that their models predict a lower number of high-tide flooding events from May 2024 through April 2025, compared to the previous year.
“So, this is the ‘regional oceanographic effects’ part of the equation. There are also numerous astronomical harmonic constituents that cause variation in our water levels,” Voss said. “Some of these harmonics have a period of up to almost 19 years,” pointing to the harmonic constituents at the NOAA Beaufort, Duke Marine Lab gauge and the Wilmington gauge.
“Regardless of the flux in water levels, the major trend is the continued rising of sea levels and an acceleration of this trend. We, along the NC coastal region, need to proactively prepare for higher sea levels and do what we can to slow climate change,” Voss continued.
