Tidal flooding in the Lowcountry has been more frequent in 2019 than any year on record, according to scientists at the National Weather Service in Charleston.
There have been 58 coastal flood events in Charleston, with three months left in the year, breaking a record set back in 2015, reported Ron Morales, a meteorologist with the Weather Service.
Last month proved record-setting by itself: 16 flood events made it the worst September on record for tidal flooding and the second of any month on record.
A record was also set for the year at the Fort Pulaski tidal gauge, near Savannah.
A flood event happens when the tidal gauge in Charleston Harbor reaches 7 feet, the point at which the Weather Service issues an advisory. That's associated with when minor flooding in low-lying areas begins, even without rain.
It's an ongoing question right now whether the Weather Service should raise the threshold at which they issue a warning, Morales said. Recent improvements in Charleston, such as check valves that stop water from upwelling through drainage pipes, have made minor flooding less noticeable and disruptive.
But he said that even if the standard were moved, that doesn't change the fact that tidal levels are creeping steadily higher as sea levels rise.
"We’ve got to be careful with those type of changes that we don’t all of a sudden put out this false sense of complacency," Morales said.
Tides are affected by several factors, but the most extreme water levels usually coincide with a new moon, full moon or period when the celestial body is in perigee, meaning it's closer to Earth than normal.
Last month's flooding was mainly driven by the new moon on Sept. 28. But other factors complicate forecasters' ability to predict an extreme tide ahead of time, Morales said.
Variables include wind direction, offshore storms, the rate of ocean currents like the gulf stream and even water temperature, because warmer water expands.
"Its not just necessarily about the local winds. It's what's going on across the whole Atlantic basin," Morales said. "All that water is doing something."
Coastal flooding is projected to accelerate in frequency as the sea level rises. Data from the same tide gauge in the Charleston Harbor shows that water is about a foot higher than a century ago.
Scientists predict that globally there could be between 1 and 8 feet of additional rise by the end of the century. The severity is hard to pin down because it's partly tied to how many planet-warming gasses from fossil fuels are released in the coming decades.
But global predictions are broad averages. Ocean rise will be higher in some locales and lower in others.
In Charleston, the 7-foot-plus tides that broke records this year could happen as often as every other day by 2045, according to estimates in the fourth National Climate Assessment. And by 2100, high tides will only get worse.
"It may be before the end of the century where every (high) tide could flood," Morales said.