Florida's version of Mother Nature has an arsenal of spectacular threats like hurricanes, tornadoes and lightning, but the deadliest is silent and nearly invisible.
Riptides, ignored and misunderstood, kill more people than any other natural phenomenon in the state. They're scarce in calm waters. Busy beaches and rough seas have lifeguards preparing for a long summer.
Jay Moyles knows riptides from personal experience.
"It feels like something has picked you up and is dragging you away from where you want to be," the Manatee County lifeguard said. "Once you're in one, you never forget it. You're like, "I never want to be in that again.' "
Two weeks ago, Moyles and other Gulf Coast lifeguards were rescuing swimmers from rip currents that nearly drowned at least four people. On April 17, an Atlantic riptide drowned a University of Florida football recruit at Melbourne Beach.
Here's the recipe for a riptide: Sometimes wind pushes lots of water past sandbars toward shore. Water piles up near the shoreline. Pressure builds until it punches a hole through an underwater sandbar.
Water rushes through the gap, creating a strong and narrow current headed straight out to sea. Swimmers and waders feel like they're caught in a river, said Jim Lushine, a meteorologist who studies riptides for the National Weather Service in Miami.
"It's like being on a water flume at Disney World," Lushine said. Except it's much scarier. The age-old lifeguard's advice _ stay calm, don't panic _ gets forgotten.
Some swimmers exhaust themselves fighting the tide. Rip currents kill about 15 people in Florida every year, Lushine said.
Riptides are more of a menace in the Atlantic's deeper waters and bigger waves. But they happen even in the relatively calm Gulf of Mexico, typically near inlets, piers and passageways through barrier islands.
Trouble spots in Pinellas County include the passes _ Bunces Pass off Fort De Soto Park as well as Hurricane, Clearwater and John's passes, said sheriff's Sgt. Greg Tita.
Pinellas hasn't had a riptide death in years, but the weather phenomenon El Nino has been whipping up the gulf waters, Lushine said. Spring and summer are the deadliest times, not because tides are worse but because there are more swimmers.
It's a dangerous mistake to swim directly against a rip current.
"You get nowhere except exhausted," said Moyles, chief of marine rescue for Manatee County.
Lifeguards advise people to either:
Swim parallel to the beach to get out of the narrow current; or
Ride the riptide to its end, then swim away from it.
"People feel like they're going to end up in Mexico, but if they just go with the flow, it'll stop 50 to 75 yards out," Lushine said.
Although riptides are often described as invisible killers, lifeguards can see them.
"It almost looks like a mushroom, with a head and a neck," Moyles said.
The "neck" is the narrow rush of water kicking up sediment and debris. The water looks dirty.
The "head" is farther out. Once the water rushes through the sandbar gap, it widens and weakens like a stream of cigar smoke.
Rip currents are more likely after storms or with high winds and choppy waves _ conditions that often attract swimmers, Moyles said. "Our beach is usually so calm and placid. When the Gulf chews up and there's whitecaps, people get excited."
Swimmers should check conditions before getting wet.
Clearwater Beach lifeguards post green, yellow or red flags to signal how strong the currents are. Sometimes they close part of the beach.
The problem isn't riptides, said Clearwater lifeguard Joe Lane. Instead, currents running parallel to shore threaten to sweep swimmers into the rougher waters of Clearwater Pass.
"There's much more current out here than people realize," said Charlie Flowers of the Clearwater Fire Department's dive team.
Few beaches in west-central Florida have lifeguards. In Pinellas, only county parks and a few city beaches are guarded. Indian Rocks Beach touts itself as the "world's safest beach" partly because of the lack of undertow.
Fort De Soto Park keeps swimmers away from trouble spots such as its southwest tip, between two fishing piers, where the water is deep and treacherous.
"When the tide turns either way, the current really rips around that point," said park supervisor Bob Browning.
He said the park's swimming beaches are safe because the water is shallow. "Unless they fall down face-first, they're not going to be in any danger."