What Is a King Tide?

CC BY 1.0. Flooding from king tide in downtown Miami, October 16, 2016. (B137/Wikimedia Commons)

The National Oceanic and Atmospheric Administration's (NOAA) National Ocean Service explains that tides are one of the most reliable phenomena in the world. "As the sun rises in the east and the stars come out at night, we are confident that the ocean waters will regularly rise and fall along our shores."'

Defined by the agency as "very long-period waves that move through the oceans in response to the forces exerted by the moon and sun," tides start in the oceans and roll toward the shores where they manifest as the regular rise and fall of the sea surface. When the highest part of these slow giant waves reaches a particular location, that is high tide; low tide corresponds to the lowest part of the wave.

The U.S. EPA notes that a king tide is not a scientific term, but one that is used to describe exceptionally high tides.

According to the EPA, a king tide is the highest predicted high tide of the year at a coastal location. It is above the highest water level reached at high tide on an average day. They are also known as perigean spring tides – the "spring" there not referring to the season, but the action.

King tides can be predicted because they occur when the orbits and alignment of the Earth, moon, and sun combine to produce the greatest tidal effects of the year; that is, when the moon is at perigee (the point in its orbit when it is closest to Earth) and the sun and Earth are at perihelion (their closest).

Although I didn't know that government agencies were allowed to mention "climate change" anymore, in a page titled "King Tides and Climate Change," the EPA explains how king tides may be used to help us anticipate a warmer world:

"King tides bring unusually high water levels, and they can cause local tidal flooding. Over time, sea level rise is raising the height of tidal systems. Average daily water levels are rising along with the oceans. As a result, high tides are reaching higher and extending further inland than in the past. King tides preview how sea level rise will affect coastal places. As time goes by, the water level reached now during a king tide will be the water level reached at high tide on an average day."

King tides on their own are proving vexing enough, but when they coincide with storms, the flooding can be severe. The video below is incredible; it's a time-lapse showing high tides over three days at Savannah Road near downtown Lewes, Delaware. Watch what happens on day three when king tides meet a coastal storm. Now imagine king tides coinciding with a hurricane storm surge and it's easy to understand all the fuss about this kind of "perfect storm."