“Every time you walk over that beach access path, the first thing you should do is look at the surf,” said Steve Pfaff, the warning coordination meteorologist at the National Weather Service in Wilmington. “How big are the waves; are there flags flying … what does the flag mean?”
Pfaff is more than a weatherman. He’s an active participant in Wrightsville Beach Fire and Ocean Rescue Department’s hurricane season training. He collects data twice daily from Wrightsville and Carolina beach lifeguards with contributions from Myrtle Beach and its surrounds, accumulating the second-largest base of rip current data nationwide. Those daily entries — broken down into wave components — help forecast rip current conditions.
The breakdown of the wave components supplied by human observers is enhanced by hard empirical data collected from offshore buoys.
“We’re looking at buoy data and we’re looking at lifeguard reports,” Pfaff said. “What we’ve been able to find was what we’re calling a wave window, a spectral wave window.”
Three wave components have led to rip current events, he said.
“We’re finding the angle of the wave is very important, the height of the wave is also very important,” Pfaff said.
The wave period refers to intervals of time between wave crests. Short sets of three small surface waves may come to shore in eight-second intervals, while bigger, rolling waves produced from groundswells may break in longer wave periods.
“We were looking specifically at a different wave period than what we’re looking for now,” Pfaff said, “so we’ve opened up the range of wave periods that have led to rip current events we might have missed had we not done the study. Certain windows of tides, around low tide, are important; but the actual range in tides isn’t as important as we thought it was originally.”
Since 2000, North and South Carolina have shared 105 rip current fatalities.
“One out of four of the drownings were from a bystander who went in to make a rescue,” Pfaff said.
Lowering the number of fatalities has led to the study of the ocean’s waves. In addition to wave angle, height and frequency, another water formation has been tossed into the stew: circulation cells.
In 2014, Spencer Rogers, North Carolina SeaGrant’s coastal construction and erosion specialist, worked with University of North Carolina Wilmington grad student Cobi Christiansen.
“They actually put buoys into a rip current to see if the circulation cell was complete — in other words, if it came back to the shore,” Pfaff said. The research was based on the work of Jamie MacMahan, associate professor at the Naval Postgraduate School in Monterey, Calif.
During the East Coast experiment in the summer of 2014, Rogers said the question asked was, “If these circulation cells exist, and we were pretty sure they did, how regular are they and how frequently does someone get ejected into deeper water? Compared to what he was finding on the West Coast we found much more irregular performance with large numbers of ejections eventually.”
The rip currents were measured with drifter buoys. Described by Rogers, each is about two feet tall, made of 8-inch diameter PVC pipe, with perforated caps at each end to allow water to pass through. A flotation ring is glued to the top and a 5-pound barbell weight is fixed to the bottom. A waterproof box is strapped to the top, a water-resistant GPS unit inside. Such an elaborate device would have cost $25,000 a decade ago but Rogers said the price of the GPS unit has dropped to $140, and the entire cost of the unit is less than $250 today.
Rogers explained he and Christiansen worked with local lifeguards to identify areas where they suspected rip currents would be present before deploying the drifters.
“We throw them in the area inside the sandbar,” Rogers said. “If there is a rip current present they will move to usually one spot and then get ejected or into circulation. … The drifters will sit around for 10 or 20 minutes and nothing happens. All of a sudden everything gets ejected. So it’s very difficult to visibly predict the risk of a rip current. … And these things record continuously so we just throw them in, multiple units at a time.”
The drifter buoys were deployed on 12 days and received good rip current data from three of those days, typically the day of or day after an offshore storm.
Had Rogers and Christiansen’s drifters demonstrated a regular pattern of East Coast circulation cells that were complete, Pfaff said, the warning model may have changed.
“The message would be for people to focus on staying afloat. In California they found the circulation cell was mainly complete so you had a better chance of the current taking you back to shore after some time,” he said.
Rogers said rip currents are the most dangerous thing on the beach, “an area that is otherwise fairly safe for recreation,” he added. “They’re highly irregular, they’re on many beaches every single day, but they’re only rarely dangerous depending on the location.”
Dividing the beach into permanent and semi-permanent locations where rip currents form, Pfaff said, “You’re going to have fixed rip currents that are near piers but they’re fixed on permanent structures.”
Wrightsville Beach Ocean Rescue Capt. Jeremy Owens said the reason there is a no-swimming zone within 200 feet of the piers is because there has always been a deep washed-out area underneath the pilings.
Semi-permanent rips form on beaches without structures, Pfaff said.
“The semi-permanent ones might be more controlled by the configuration of the sand bars. … A storm comes by and it might change the whole configuration of the shoreline,” he said. “We’ve had many of these events where the weather is beautiful but the surf is roughed up from a distant storm and we can’t equate good weather to good surf. It doesn’t work that way.”
Tips from the experts:
• Carry a flotation device to the beach.
• Pay attention to the flags.
• If you see someone in trouble, find a lifeguard or call 911.
• Try to direct the person to swim out of the rip current with hand signals.
• Don’t panic. If caught in a current, swim parallel to the shoreline for 20-50 feet.
• If in doubt, don’t go out.
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