As a strengthening Hurricane Idalia heads for landfall along the Florida Gulf Coast, forecasters are warning of a “catastrophic storm surge expected in Big Bend region of Florida due to storm surge.”

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And while the Tuesday 11 a.m. EDT National Hurricane Center update has estimated that storm surges could be 10-15 feet between the Aucilla River and Yankeetown, some on social media are asking about a type of tide that could push the water even higher.

The term “king tide” is trending in some places.

King tides, or unusually high tides that happen when the moon is closest to the Earth would have a major effect on a landfalling system.

How would king tides affect what happens with Idalia? Here’s a look at king tides and what they do.

What is a king tide?

The term “king tide” is a term used to describe an especially high tide event. It is not a scientific term.

What causes a king tide?

The tides happen when there is an alignment of the gravitational pull between the sun and moon in the Northern Hemisphere, according to the National Oceanic and Atmospheric Administration.

“Twice a year when the Earth, sun and moon line up, when the moon and the sun are at perigee and perihelion, we generally experience the greatest tidal ranges of the year,” according to the North Carolina King Tides Project.

What are perigee and perihelion?

Perigee is the point when the moon is closest to the Earth. Perihelion means a point in the orbit of a planet (in this case Earth), that is nearest to the sun.

What does this have to do with tides?

A few times a year, in the spring and fall, the new or full moon coincides with the perigee of the moon.

During full or new moons average tidal ranges are slightly larger. A new or full moon occurs when the sun, earth and moon are in near alignment. The tides this alignment creates are slightly higher than average tides and are called the “perigean spring tides.”

What happens when they occur near the time a tropical system makes landfall?

A tropical system pushes water inland in advance of making landfall. If that happens during a perigean spring tide, it pushes an already abnormally high tide, even higher, adding to property damage and coastline erosion.

King tides do not raise the water levels by an extraordinary amount, but they do raise them.

Will it happen with Idalia?

It could, depending on timing. The king tide is expected between noon and 2 p.m. on Wednesday in the area where the storm is likely to make landfall, according to The National Weather Service.