Smithsonian.com

A rip current on the Florida coast in 2004 after Hurricane Jeanne (Courtesy of Dennis Decker, WCM, NWS Melbourne, FL/NOAA)

The U.S. East Coast is likely to miss out on most of the destructive forces of Hurricanes Danielle and Earl this week, with both just skimming by off the coast. But a miss on land doesn’t mean that the storms have no effect. In fact, they’ve both brought powerful waves and, more worrisome, rip currents. This past weekend, lifeguards rescued 250 people from the killer currents. One man in Ocean City, Maryland was swept out to sea and never found.

Rip currents—a.k.a. rip tides—can form anywhere there are waves, including on the shores of the Great Lakes. Around 100 people die every year after being caught in these currents. They quickly channel water, and anyone caught in the current, away from shore. They’re dangerous not because they pull people under (they’re only surface currents) but because they usually catch people unaware; swimmers don’t notice the rip current in the heavy surf.

The rip currents form because of complex interactions between incoming waves, currents and bathymetry (the structure of the ocean bottom). The National Weather Service explains the basic mechanics:

• Waves break on the sand bars before they break in the channel area.
• Wave breaking causes an increase in water level over the bars relative to the channel level.
• A pressure gradient is created due to the higher water level over the bars.
• This pressure gradient drives a current alongshore (the feeder current).
• The longshore currents converge and turn seaward, flowing through the low area or channel between the sand bars.

Your best strategy for dealing with a rip current is simply to avoid them and if you don’t know how to swim, to stay completely out of the water. But if you find yourself being dragged out to sea, don’t panic and don’t try to fight the current and swim back to shore. You’ll tire yourself out. Instead, swim parallel to the shore to get out of the current and then head back to the sand. If you can’t manage that, signal to a lifeguard that you need help and concentrate on staying afloat.