Examining What Fuels Deadly Rip Currents

USF research may result in better safety forecasts and more lead time to warn swimmers.


TAMPA, Fla. (May 16, 2011) – On a single day – June 8, 2003 – eight people drowned in rip currents along Florida’s Panhandle beaches. Now remembered as Black Sunday, the currents claimed both the lives of swimmers caught by surprise and the people trying to rescue them.

Florida is no stranger to rip current deaths, easily leading the nation with 234 fatalities and another 199 injuries in a 15-year period studied by University of South Florida weather researchers. Their research shows that in addition to better safety education and measures, a better understanding of the weather patterns that typically proceed the formation of potentially deadly currents is needed.

Charles Paxton, the Science and Operations Officer for the National Weather Service office in Ruskin who also is completing his Ph.D. in USF’s Department of Geography, Environment, and Planning, has analyzed the wind and sea level pressure readings in the days before rip current deaths occurred and found common patterns which could aid in warning swimmers and staffing beaches with lifeguards.

The National Oceanic and Atmospheric Administration provides daily rip current forecasts and warnings, but Paxton’s research indicates that beachgoers might actually be able to know days in advance if they need to take more precautions.

Working in conjunction with USF Assistant Professor Jennifer Collins, Paxton’s research shows that analyses of wind and sea level pressure from the waters surrounding the lower 48 states indicate common weather patterns associated with rip current deaths and injuries.

“Forecasters who predict rip currents may be able to provide more lead time for ocean rescue services to plan for staffing,” Paxton said, “particularly when other conditions such as weekends with warmer water temperatures, and sunny skies may lead to a busy beach day.”

Florida beaches are especially vulnerable because the sandy bottoms are constantly shifting shape, said Paxton, an avid surfer. Rip currents form when water from breaking waves that has collected in the shallows is funneled seaward through a narrow channel, creating a powerful stream of water that swimmers can’t see and don’t know is there until they are in it.

The researchers created composite analyses of wind and sea level pressure from the waters surrounding the continental U.S. to examine what weather patterns were associated with rip current deaths and injuries.

They found that weather patterns related to rip currents in Florida and the Gulf Coast states were associated with strengthening of semi-permanent subtropical high pressure also known as the “Bermuda High”. As the high strengthens, so do the winds and waves. A similar area of high pressure has comparable impacts for Southern California. At higher latitudes, rip currents were typically associated with a combination of semi-permanent high pressure and migrating areas of low pressure.

The researchers found in most cases, it was wind-driven waves towards the beaches that produce the conditions leading to rip currents.

Paxton, an avid surfer who spends many hours at the beach, has more than a casual interest in rip currents. He has authored a chapter in the book examining cutting-edge current modeling technologies, “Rip Currents: Beach Safety, Physical Oceanography, and Wave Modeling” whose co-author is Stephen Leatherman of Florida International University, better known as “Dr. Beach.”

Noting that education is the first step in safety planning, Paxton said more knowledge could help save lives in more ways than one. The sandy beaches can drop off abruptly into deeper water and beachgoers often wade out to near the drop-off then get pulled out by a rip current just far enough to cause them to panic.

But Paxton also found that onshore winds contribute to deadly rip currents because the rough choppy waves can obscure the view of a swimmer struggling in the water. To escape a rip current, the swimmer should avoid panic and swim parallel to the beach to break free from the current.

“I have seen people panicking in the water and there is no reasoning with them,” Paxton said. “If they have nothing to grab on to, they will pull their rescuer under.”

The researchers noted that many beach access points now have standardized signs with diagrams showing swimmers how to survive a rip current, but said stronger wording similar to that used at Ocean Beach on the Pacific Ocean in San Francisco may keep weaker swimmers out of the water.  Those signs read: “Danger Rip Currents - PEOPLE SWIMMING AND WADING HAVE DROWNED HERE.”

Florida Rip Current Facts:

·      Florida had far more rip current victims than any other state with 236 deaths from 1994-2009 compared to California in second place with 43 deaths. North Carolina (36 deaths), Alabama (23 deaths), and New Jersey (22 deaths) round out the top five states with the most rip current victims.

·     Florida has almost 2,000 km of coastline and 1,067 km of beaches. Florida also has the warmest water of any state in the shallow Gulf of Mexico waters.

·     Many of the drowning victims are tourists who are unfamiliar with ocean waters.

The National Weather Service Surf Zone Forecast: http://forecast.weather.gov/product.php?site=TBW&issuedby=TBW&product=SRF&format=CI&version=1&glossary=1