Tides represent the rhythmic rise and fall of sea level. The “King Tide” stands out as the highest non-storm-related tidal event of the year. While not a formal scientific designation, this widely used term describes unusually high water levels that noticeably impact shorelines and infrastructure. Observing a King Tide provides a temporary glimpse into the maximum extent of current tidal forces.
The Astronomical Mechanics of King Tides
The occurrence of a King Tide is rooted in a specific alignment of celestial bodies that maximizes gravitational forces on Earth’s oceans. These events are technically known as perigean spring tides. A spring tide occurs about twice a month when the Earth, Moon, and Sun are in syzygy—a straight-line alignment—during a new or full moon. This alignment causes the gravitational pulls of the Sun and Moon to combine, resulting in the highest high tides and the lowest low tides. The perigean element further amplifies this effect, referring to the Moon being at its closest point to Earth in its elliptical orbit, a position called perigee. This combination causes the most extreme tidal range, distinguishing the King Tide from a regular spring tide.
Predictability and Timing
King Tides are highly predictable because they are governed by the consistent, long-term cycles of the Earth, Moon, and Sun. These extreme high tides typically occur once or twice annually, though the exact number can vary by location. Scientists can forecast the precise dates and heights of these events years in advance using astronomical calculations. The timing is often influenced by the Earth’s elliptical orbit around the Sun. When Earth is closest to the Sun, a point known as perihelion, the Sun’s gravitational pull on the tides is stronger. Perihelion occurs around early January, which is why the Northern Hemisphere often experiences its most extreme King Tides during the winter months.
Observable Effects on Coastal Areas
The most immediate and visible effect of a King Tide is the temporary inundation of low-lying coastal zones. This phenomenon is frequently referred to as “sunny day flooding” or “nuisance flooding” because it occurs without storms, heavy rain, or high winds. The unusually high water level simply overtops existing tidal barriers and reaches areas normally far from the high-tide line. This flooding can strain local infrastructure by covering coastal roads and parking lots, sometimes forcing temporary closures. Storm drains and drainage systems can also become overwhelmed, as the high ocean water prevents them from effectively draining surface runoff.
Contextualizing King Tides and Sea Level Rise
King Tides are naturally occurring astronomical events and are not directly caused by climate change. However, these events have become increasingly relevant as a way to visualize the impacts of long-term sea level rise. Because of thermal expansion and melting land ice, the average baseline sea level has risen globally by about eight inches since 1900. This rise means that the naturally occurring King Tide is starting from a higher water level than it did decades ago. Today’s King Tides offer a preview of what the future’s average daily high tides may look like as sea levels continue to increase.