SAVANNAH, Ga. (WSAV) — During the first weekend of November 2021, high tides along coastal Georgia and South Carolina were abnormally high which lead to coastal flooding.
There were several reasons as to why the high tides became such a concern for us. To understand why they were so high, first, we’ll talk about what causes tides and why some tidal cycles are normally more extreme than others.
Why We Have High & Low Tides
Tides are the regular rise and fall of water levels along the coast and are essentially very long-period waves that move through the ocean due to the gravitational pull of the moon and sun. This wave originates in the ocean and then moves toward the shoreline and causes the level to go increase and then decrease.
Gravity is one of the major forces that work to create tides. The moon and the sun’s mass work to pull on the surface of the ocean. Since the moon is much closer to the earth than the sun, its gravitational force is much greater than the sun. The sun’s effects on generating tides are about half of what the moon generates.
The pull of the moon and sun cause the high and low tide by creating a bulge of water toward the moon. The rotation of the earth creates another bulge of water away from the moon. The bulge of water is the high tide. In between is where you have a low tide.
There are times in the year where tides are much higher than what is considered normal or lower than normal for a location. Higher than normal tides from a full moon or new moon are called spring tides or “king tides.”
Spring tides have a greater range between high and low tide because the tidal bulge around the earth becomes bigger due to a greater gravitational pull of the moon and the sun. This is possible because the moon, earth, and sun are directly aligned.
The term spring tide is a little misleading since they happen any time of the year, regardless of the season. They actually happen twice during a lunar cycle.
On Nov. 7, we had a new moon meaning we were experiencing spring tides. But why were they so much higher this time?
Wind Effects On Tides
At the same time as the new moon, we were dealing with a developing and strengthening low-pressure system located just off of our coast.
At the height of the storm on Saturday, this system started to take on characteristics of a Nor’easter, just like New England experiences many times each winter. Locally, this storm was producing heavy rain and strong and gusty wind. Wind gusts were as high as 50 mph at the coast and even higher offshore.
The primary wind direction was from the northeast, like with any Nor’easter type of storm system. This helped more water to collect near the coast in a similar fashion as storm surge.
How High The Tide Was
Since the offshore storm developed at the same time as the November spring tide, water levels were able to become much higher than they would have if we just had the astronomical tides alone or the storm alone.
The high tide at Fort Pulaski on Nov. 7 reached the fourth-highest level on record at 10.45 feet. This led to numerous road closures Sunday morning.
Tropical systems caused the tide to be higher three other times at Fort Pulaski. Hurricane Matthew on Oct. 8, 2016, at 12.56 feet, Hurricane Irma at 12.24 feet on Sept. 11, 2017, and Hurricane 9 at 10.86 feet on Oct. 15, 1947.
More tides and flooding like this are expected to become more likely as the sea level slowly increases. At the Fort Pulaski tide gauge, tide levels have reached 10 feet or more 21 times. Fourteen of those times at 10 feet or more have been since 2014