{"id":15432,"date":"2021-09-16T08:39:59","date_gmt":"2021-09-16T12:39:59","guid":{"rendered":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/?page_id=15432"},"modified":"2024-08-19T11:51:31","modified_gmt":"2024-08-19T15:51:31","slug":"model-behavior","status":"publish","type":"post","link":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/model-behavior\/","title":{"rendered":"Model Behavior"},"content":{"rendered":"\n\n\n\n\n

Several years ago in late September, Bob Schiffer rode his bike to the beach at Kill Devil Hills for a dip in the ocean, as he often did. Before heading to the water, he hung up his backpack on a pole with a waving red flag \u2014 a no-swimming alert indicating hazardous surf conditions. His plan was to repeatedly propel himself, porpoise-style, through shallow water, then backstroke to where he had started as part of a strength-building exercise he had practiced numerous times.<\/p>\n\n\n\n

The sea was turbulent that day, with waves breaking in all directions, recalls Schiffer, who at the time lived on the Outer Banks. He had barely begun his routine when he suddenly discovered that he was nowhere close to the beach. \u201cIt happened as if I were on an express train,\u201d he says, and \u201cI realized I was in a rip\u201d \u2014 that is, a narrow current of water flowing away from shore.<\/p>\n\n\n\n

\"Top:
Top: Red flags signal no swimming because of hazardous surf conditions. Photo: Robert Alford\/Shutterstock. Bottom: Signs of a rip current include a narrow gap of darker, seemingly calmer water between areas of breaking waves and whitewater. Photo: NOAA<\/figcaption><\/figure>\n\n\n\n

As a teenager growing up in New York City, Schiffer served as a beach lifeguard. He knew the common safety protocol: If you\u2019re caught in a rip current, try to break free by swimming parallel to shore. Otherwise, float and call for help.<\/p>\n\n\n\n

The churning water made swimming futile. Spying bystanders in the distance, Schiffer yelled for someone to call 911. Then he tried to relax, turning the face of his watch away from sight so he wouldn\u2019t dwell on the time.<\/p>\n\n\n\n

About 40 minutes later, help came splashing toward him. David Elder, lifeguard and supervisor of Kill Devil Hills Ocean Rescue, had received the distress call and arrived with a torpedo-shaped float. Schiffer grabbed hold and together they kicked back to shore.<\/p>\n\n\n\n

The next day, the two ran into each other at a local caf\u00e9. Schiffer remembers wearing a rain slicker and that Elder pointed to its off-white interior, noting, \u201c\u2018That\u2019s the color of your complexion when I came to see you.\u2019\u201d In the ocean, treading water at what seemed like 50 yards from shore, Schiffer wasn\u2019t aware of how drained he\u2019d become.<\/p>\n\n\n\n

Rip currents are the leading cause of death on surf beaches worldwide. Preliminary data collected by the National Weather Service suggests that in 2020, 65 rip-current related fatalities occurred in the United States and Puerto Rico. But that number doesn\u2019t reflect unreported or undocumented drownings. (In this article, \u201cdrowning\u201d implies fatality.)<\/p>\n\n\n\n

Given that the majority of drownings occur on unguarded beaches or outside of regular beach patrol times, the actual U.S. death rate could be more than 100 a year, according to U.S. Lifesaving Association (USLA) executive director Chris Brewster and colleagues, reporting in Natural Hazards and Earth System Sciences<\/em><\/a> in 2019.<\/p>\n\n\n\n

This public safety threat has driven researchers to devise ways to predict hazardous rips. Until recently, efforts centered on a tool first pioneered in the 1990s, which National Weather Service forecasters have tailored to their locales. Just this past spring, the National Oceanic and Atmospheric Administration officially launched a new model designed to provide more precise and timely forecasts than ever before.<\/p>\n\n\n\n

The tool combines lifeguard observations of rip currents and rescue reports with artificial intelligence to deliver an hourly forecast up to six days out for many U.S. coastlines \u2014 including in Hawaii, Puerto Rico, and Guam. Greg Dusek, NOAA senior scientist and project lead, says that with additional refining, forecasts will be available for the entire continental U.S., and even the Great Lakes, \u201chopefully not too far down the future.\u201d<\/p>\n\n\n\n

Ultimately, researchers aspire to warn swimmers of rip currents on their specific stretch of shore \u2014 in real time.<\/p>\n\n\n\n

\u201cOur long-term vision is that as a beachgoer points their smartphone at the beach, they will be alerted to locations where there are potential rips,\u201d says Alex Pang, a computer scientist at UC Santa Cruz and a colleague of Dusek\u2019s. In short, \u201cwe want to save lives.\u201d<\/p>\n\n\n\n

Wading In<\/h2>\n\n\n\n
\"Kill
Kill Devil Hills Ocean Rescue lifeguard Reggie Kelly holds a yellow flag, warning swimmers to be cautious of strong currents. Photo: Kill Devil Hills Ocean Rescue<\/figcaption><\/figure>\n\n\n\n

Back in the early 2000s, lifeguard David Elder was becoming increasingly frustrated with the number of rip-related close calls and fatalities that his team was encountering. He wondered if there was a way to improve rip current forecasting, particularly for the sake of people on unguarded beaches.<\/p>\n\n\n\n

\u201cWhat I realized was the problem that we were experiencing was a lack of knowledge and an inability of the average patron to be able to understand what a rip current was,\u201d says Elder, who has over 30 years of lifeguarding experience, and whose team has advanced certification from the USLA. \u201cWe need to inform them about [rips] in a more timely manner,\u201d he adds \u2014 before they set foot on the sand.<\/p>\n\n\n\n

Rip currents occur along beaches with breaking waves, including some Great Lakes shorelines. But their mere existence doesn\u2019t spell danger. Speed is one key determinant. Many rip currents are so languid that swimmers won\u2019t notice them. Others \u201ccan exceed the fastest Olympic swimmers at their worst,\u201d says Spencer Rogers, North Carolina Sea Grant\u2019s coastal erosion and construction specialist.<\/p>\n\n\n\n

Lifeguards are expertly trained to spot dangerous rips \u2014 not by their speed, which is nearly impossible to detect with the naked eye \u2014 but by recognizing other signature traits, such as a narrow band of darker, seemingly calmer water between breaking waves on either side.<\/p>\n\n\n\n

Guards also recognize when weather and ocean conditions have aligned such that rescues will be likely. \u201cThe really dangerous days are blue-sky, nice weather on the beach, with local wave-generating conditions that make high-velocity rip currents that are very, very dangerous,\u201d says Rogers, who has served on a national rip current task force with NOAA, NWS, and USLA partners. \u201cThose are the days where we have the most fatalities and the most rescues, because it doesn\u2019t look threatening.\u201d<\/p>\n\n\n

\n
\"Information<\/a>
Photo: John McCord\/Coastal Studies Institute<\/figcaption><\/figure><\/div>\n\n\n

The probability that a hazardous rip current will occur is what drives NOAA\u2019s new forecasting tool. In other words, it hinges on the question, \u201cHow likely is this rip current to cause a swimmer distress?\u201d says Dusek, who began the project as a Ph.D. student at the University of North Carolina at Chapel Hill.<\/p>\n\n\n\n

Broadly speaking, three major factors contribute to rip current formation: wave conditions, tide, and the shape of the sea floor, or bathymetry. To build his model, Dusek had to figure out how to weight those factors such that their relationship predicted dangerous rips.<\/p>\n\n\n\n

For help, he turned to Elder, who supplied him with a set of lifeguard observations and rescue reports from the summers of 2008 and 2009. Dusek then plugged historical ocean and weather data into the model to see how accurately it predicted hazardous rips reflected in the lifeguard data, tweaking the tool as necessary.<\/p>\n\n\n\n

Using human observations \u2014 albeit ones rooted in expertise \u2014 to hone a computer model might raise eyebrows. \u201cThat kind of more qualitative observation, at first, could seem less powerful than a very quantitative speed measurement, but for the purposes of developing a hazard forecast, it\u2019s actually perfect,\u201d says Melissa Moulton, a coastal physical oceanographer at the University of Washington in the Applied Physics Laboratory and at the National Center for Atmospheric Research.<\/p>\n\n\n\n

A few years ago, Moulton and Dusek tested the model against measurements that she and scientists from Woods Hole Oceanographic Institution had recorded with current meters submerged off the U.S. Army Corps of Engineers Field Research Facility in Duck. They wanted to see if the model predicted hazardous rips when the meters had recorded strong currents going offshore.<\/p>\n\n\n\n

\u201cWe found that those totally different types of observations were remarkably consistent with each other,\u201d she says. \u201cI was really surprised how the lifeguard-derived hazard model and me, sticking a current meter in water, gave such a similar answer for the way that waves and tides control the presence of strong rip currents.\u201d The team published their study in Weather and Forecasting<\/em><\/a> in 2017.<\/p>\n\n\n\n

Over time, Dusek and NOAA colleagues have improved the model with additional lifeguard observations from other beaches in and outside of North Carolina. Indeed, the suite of conditions that promote hazardous rip formation along our state\u2019s barrier island shoreline aren\u2019t identical to those along, say, rocky West Coast beaches. The model must crunch numbers differently depending on where it\u2019s forecasting.<\/p>\n\n\n\n

\u201cThe baseline model that we trained in North Carolina worked pretty well everywhere else we tested,\u201d Dusek says, and yet \u201cwe can improve it dramatically if we have good observations in other places.\u201d<\/p>\n\n\n\n

Filling in Gaps<\/h2>\n\n\n\n

In March 2021, Dusek\u2019s rip current model debuted as part of NOAA\u2019s Nearshore Wave Prediction System, a tool that forecasts wave conditions, overwash, and erosion. The system seamlessly provides data for the rip model to make its predictions.<\/p>\n\n\n\n

Many National Weather Service Forecast Offices are now using the new rip forecasts in conjunction with an older forecasting method to issue their rip guidance. The traditional method \u2014 which entails manually entering values for different weather and ocean conditions into a spreadsheet \u2014 has limitations for which the new model helps compensate, says Steve Pfaff, warning coordination meteorologist for the NWS Forecast Office in Wilmington.<\/p>\n\n\n\n

\u201cI think this is a great leap forward,\u201d Pfaff says. For decades, forecasters have been \u201chamstrung, only able to provide a composite rip current risk for the beaches of an entire county.\u201d The new model\u2019s resolution enables meteorologists to home in on mile-long sections and provides hourly forecasts nearly a week in advance.<\/p>\n\n\n\n

In addition, whereas the old method relied on a three-tier warning structure \u2014 low risk, moderate, or high \u2014 the new model provides a zero to 100% probability of hazardous rips occurring, similar to a rain forecast.<\/p>\n\n\n\n

\"Rip
Rip currents occur on surf beaches around the globe. The rocky structure at the bottom of the frame likely contributed to this rip, photographed in Australia and distinguishable by a swirling sediment plume. Photo: GUAVWA\/Shutterstock<\/figcaption><\/figure>\n\n\n\n

When Dusek and his doctoral advisor, Harvey Seim of UNC-Chapel Hill, first described the model in 2013 in the Journal of Coastal Research<\/em><\/a>, they noted a 67% improvement over the old forecasting method for Kill Devil Hills. Since then, Dusek says, \u201cpretty much everywhere we test, we see an improvement with the new approach, with obviously the added benefit [that] we\u2019re not just giving you one value for today; we\u2019re giving you much more information going much further into the future.\u201d<\/p>\n\n\n\n

\u201cIt\u2019s really the first time we\u2019ve had sophisticated numerical model guidance for rip currents that goes out that far and for that many beaches,\u201d adds Mark Willis, Wilmington\u2019s meteorologist in charge.<\/p>\n\n\n\n

From a planning perspective, advance warning is crucial to emergency managers. Case in point: This past August, the University of North Carolina Wilmington was hosting an event on Wrightsville Beach, and the school\u2019s emergency manager was concerned about the rip current risk.<\/p>\n\n\n\n

Combining the old and new rip forecasting approaches, \u201cwe were able to say with a higher level of confidence, yes, there\u2019s a moderate risk of rip currents for New Hanover County \u2014 in particular, Wrightsville Beach today \u2014 and we think that the rip probabilities will be highest during the morning,\u201d Pfaff says.<\/p>\n\n\n\n

On the Horizon<\/h2>\n\n\n\n

Despite years refining his model, Dusek acknowledges that \u201cthere\u2019s still a lot of work to do.\u201d<\/p>\n\n\n\n

One important limitation is the tool\u2019s treatment of bathymetry, a critical factor in rip current formation. For instance, channel rips can occur when a break between sandbars or reefs creates a conduit for water flowing back out to sea.<\/p>\n\n\n\n

But capturing data on a constantly shifting sea floor is difficult, to say the least.<\/p>\n\n\n\n

\u201cWhat\u2019s going on under the water, in the surf, is changing so fast and [is] so hard to measure,\u201d says Moulton, the coastal physical oceanographer.<\/p>\n\n\n\n

The rip model currently uses an approximation for bathymetry; specifically, it considers whether a big storm occurred several days prior to a given forecast. \u201cFrom our research data we saw that, following a storm \u2014 you know, a pretty large wave event \u2014 the shape of the bottom would end up being pretty favorable to rip currents,\u201d Dusek says.<\/p>\n\n\n\n

Nor does the model yet account for the influence of structures, such as groins, jetties, and piers, which can promote rip currents as incoming waves deflect. Such structures can also influence how sediment moves and thereby affect bathymetry.<\/p>\n\n\n\n

Dusek also plans to further improve the model using data beyond lifeguard observations. \u201cEven though lifeguards are really good at doing this, there\u2019s going to be different interpretations depending on where you are,\u201d he says, \u201cso a lifeguard in Kill Devil Hills, North Carolina, is probably going to see the beach differently than a lifeguard in San Diego, California.\u201d Plus, most beaches don\u2019t have guards, so many nearshore nuances go unobserved.<\/p>\n\n\n\n

\"Examples
Examples of virtual overlays delineating a rip current. Images: Courtesy of Alex Pang\/UC Santa Cruz<\/figcaption><\/figure>\n\n\n\n

Dusek and colleagues think surf webcams \u2014 internet-connected cameras attached to stationary structures like piers \u2014 could provide missing data. The idea is that a camera would capture video of the surf, and a computer would analyze the imagery for tell-tale signs of dangerous rips. Positive identifications would then be used to enhance the rip current model.<\/p>\n\n\n\n

Alex Pang of UC Santa Cruz is developing that technology using a process called machine learning; the team is testing its capability using footage from a regional array of webcams operated by the Southeast Coastal Ocean Observing Regional Association.<\/p>\n\n\n\n

Dusek and Pang\u2019s ultimate goal is to enable beachgoers to use their own smartphones to detect rip currents in real time. They envision docking stations located on elevated locations, such as piers and beach access points, where visitors can position their phones, open an app, and take steady footage of the shoreline in front of them. The app would then reveal dangerous rips with a virtual overlay marking their path, similar to Instagram filters that stick \u201cwhiskers and funny noses over someone\u2019s selfie,\u201d Pang says.<\/p>\n\n\n\n

Pfaff says the concept is promising. Seeing a rip current illuminate on your phone \u201chas a sense of realness to it,\u201d he notes. \u201cAs far as an educational tool, I think that\u2019s amazing.\u201d<\/p>\n\n\n\n

Getting the Message<\/h2>\n\n\n\n

The rip current that Bob Schiffer survived in Kill Devil Hills wasn\u2019t his last. This past June, he and his daughter and grandson were playing in the surf at Ocean City, Maryland, when he discovered that he was again caught in a rip.<\/p>\n\n\n\n

The prospect of drowning in front of loved ones filled Schiffer with anxiety, and he began frantically swimming. \u201cYears of training and experience were erased by a flash of emotion,\u201d he says.<\/p>\n\n\n\n

Schiffer\u2019s family escaped to shore, where his daughter immediately sought help. Once again, a lifeguard pulled him out of the water, shaken but unscathed.<\/p>\n\n\n\n

In retrospect, Schiffer says he overlooked certain realities that likely contributed to the close call: He\u2019s older, he hadn\u2019t been in the ocean in a while, and, having once been a competitive swimmer, he fancied himself somewhat invincible.<\/p>\n\n\n\n

Not everyone will experience such an epiphany. An enhanced rip current forecast is one step to saving more lives, but a prediction is only as good as the messaging around it. In that regard, building public awareness \u201chas a long way to go,\u201d says Pfaff.<\/p>\n\n\n\n

Elder agrees. \u201cHow do you tell a 55-year-old male and a 19-year-old kid the same message? And where do you tell them that, and how do you say it?\u201d<\/p>\n\n\n\n

\u201cThis is something I\u2019m passionate about,\u201d Elder adds, \u201cbecause I can see the faces in front of me, right now, who should have known this stuff and who will never get a chance to.\u201d In North and South Carolina alone, more than 170 people have drowned in rip currents since 2000.<\/p>\n\n\n\n

For Schiffer\u2019s part, he\u2019s changing his ways. \u201cI\u2019m accustomed to swimming alone, and was accustomed to swimming early before the beach opened,\u201d he says. \u201cI\u2019ve now made a pact with my children, my daughters, that Grandpa will no longer do that, that I will abide by all of the reasonable standards.\u201d<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

By the Numbers<\/h3>\n\n\n\n

Anyone can get caught in a rip current. The map above \u201chighlights the need to talk about rip currents not only within coastal areas, but also in cities well inland, across the country,\u201d says Victoria Oliva, a meteorologist with the NWS Forecast Office in Wilmington. \u201cWhether someone lives in Greensboro, North Carolina, or Kentucky, if they ever visit a beach, they need to be aware of rip currents \u2014 what they are and how to stay safe.\u201d<\/p>\n\n\n\n

The Wilmington office provided the rip current-related statistics below. The data applies to North and South Carolina and extends from 2000 through July 31, 2021, except where noted.<\/p>\n\n\n\n