Hurricane Matthew (copy)

Hurricane Matthew brought high surf to Folly Beach in 2016. A "meteotsunami" might have made it worse, research suggests. File/Brad Nettles/Staff 

Punishing heat, rip currents, thunderstorms — the beach could have more torment in store this summer in the form of tiny tsunamis.

It turns out a fast-moving summer thunderstorm can roil up a set of these sucking waves.

South Carolina sees more than half a dozen "meteotsunamis" per year, according to a recent National Oceanic and Atmospheric Administration study.

Nearly all of them are only a half-foot higher or less than the surf around them, a sort of rogue wave.

Charleston Parks and Recreation beach park staffers say they haven't taken notice of any. But it's one more reason to be careful out there, especially when a storm rolls up.

The National Weather Service has begun alerting stations when those conditions are in place, said Greg Dusek, NOAA oceanographer and senior scientist, who was the study's lead author.

"Always be mindful" of the forecast and conditions, he said.

About 25 meteotsunamis per year strike the East Coast, the NOAA study found. The Carolinas tend to draw a few more than other states because of the shapes of their individual coastlines.

Myrtle Beach sees more than seven per year.

A lot of the mini tsunamis are the result of tropical storms or hurricanes offshore. The danger in that is they make the already punishing storm surge surf worse, Dusek said.

Occasionally, they seem to come out of nowhere. A set of meteotsunami waves about two feet high struck Barnegat Inlet in New Jersey in 2013, dragging divers up and over a breakwater, the study noted. That was caused by a line of thunderstorms racing offshore.

Researchers noted a similar set of two-foot high waves struck Myrtle Beach during October 2003 when a tropical storm was passing offshore, Dusek said.

"We know they happen at the same time (as tropical systems)," he said. "They might not be huge waves, but if you add (two feet) above your storm surge that could be significant," he said.

The waves also tend to roll up on top of the surging surf from northeast winds in the winter, Dusek said.

A tsunami large enough to cause widespread damage on the South Carolina coast is the classic low-probability, high-impact event. But they too can happen, like the earthquakes that tend to stir them. 

In 2014, a powerful quake erupted in a trench off Puerto Rico just after midnight. If it had triggered a slide down the walls of that 5-mile deep trench, a sizable tsunami could have struck the Charleston coast before dawn, geologists said.

If that quake had been a monstrous magnitude 9, like the catastrophic 2004 Indian Ocean quake, the walls of water slamming into the coast here could have been 5 feet or more above surf, enough to put the Isle of Palms under water and submerge much of the other inhabited barrier islands and Lowcountry waterfront.

Thousands of people could have been in harm's way. And unlike a storm surge, a tsunami is a series of rapid inundations and retreats. The coast would been thrashed in a washing machine effect.

After the Indian Ocean tsunami in 2004, advances have been made in detecting, forecasting and improving safety. The measures include more monitoring stations, 24 hour-staffed warning centers and an education effort that has certified 28 states and territories as "tsunami-ready."

Charleston County is among the areas certified, and the signs are ubiquitous along the coast.

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Reach Bo Petersen at @bopete on Twitter or 843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.

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