King tides are the highest astronomical tides that occur each year. These exceptional high tides happen when multiple factors align to create spring tides with extra gravitational pull.
What Are King Tides?
King tides are not a scientific term, but rather a colloquial name for the highest predicted high tides of the year. They occur when the moon is at its closest to Earth (perigee) during a new or full moon, creating spring tides with extra force.
These extreme tides can be 1 to 2 feet higher than normal spring tides. In some areas with large tidal ranges, like the Bay of Fundy, the difference can cause significant coastal flooding, especially when combined with storms, high winds, or heavy rainfall.
When Do King Tides Occur?
King tides happen several times per year, typically during winter months in the Northern Hemisphere. The exact timing depends on the alignment of several astronomical factors:
- Perigee: When the moon is closest to Earth in its elliptical orbit
- New or Full Moon: When sun, moon, and Earth align for spring tides
- Earth Perihelion: When Earth is closest to the sun (early January)
Most coastal areas experience 2 to 4 king tide events per year. These events are predictable and can be forecast years in advance using astronomical data.
The Science Behind King Tides
King tides result from the combined gravitational effects of the sun and moon when multiple factors amplify tidal forces. The moon orbit around Earth is elliptical, not circular. At perigee, the moon is about 30,000 miles closer to Earth than at apogee. This closer distance increases the moon gravitational pull by about 20 percent.
When perigee coincides with a new or full moon, the result is an exceptionally high spring tide, which we call a king tide.
King Tides and Climate Change
King tides provide a valuable preview of future sea levels. As global sea levels rise due to climate change, today king tides show what tomorrow normal high tides might look like.
Many coastal communities use king tide events to identify vulnerable infrastructure, test flood prevention systems, educate residents about sea level rise, and plan for future coastal adaptation.
Conclusion
King tides are the highest astronomical tides of the year, occurring when multiple factors align. Understanding king tides helps coastal communities prepare for extreme high water events and provides a preview of future sea levels.