What Is A King Tide?
QUICK ANSWER
A king tide is the highest predicted high tide of the year, occurring a few times annually when spring tides coincide with the moon's closest approach to Earth (perigee). King tides cause exceptionally high water levels at coasts, sometimes flooding low-lying areas even without storms. They preview future sea level rise impacts.
King tides are the highest predicted tides of the year, when astronomical alignment produces exceptional high water at coasts worldwide. They're not unusual events but predictable ones, with dates known years in advance. King tides have become important as previews of sea level rise impacts, showing how rising baseline water levels will affect coasts in coming decades.
What makes a king tide?
A king tide (technically called a perigean spring tide) requires two astronomical conditions occurring together. First, it must be a spring tide period (new moon or full moon when sun and moon align). Second, the moon must be at or near perigee, its closest point to Earth in its elliptical orbit. The moon's distance varies by about 14% between perigee and apogee. When closest, the moon's tidal force is stronger than average. Combining a spring tide with perigee produces the highest predicted tides of any astronomical cycle.
How high do king tides reach?
King tides typically reach about 6-12 inches higher than average high tides, depending on location. In places with normally large tide ranges, the additional height can be very significant. Some coastal areas experience flooding during king tides even without storms or unusual weather. The extra height can make the difference between coastal areas staying dry and flooding noticeably. As sea levels rise from climate change, king tides reach higher absolute levels each decade, increasingly causing flooding in previously dry areas.
When do king tides happen?
King tides occur a few times each year, typically in winter months (December to February) in the Northern Hemisphere when Earth is closest to the sun and other astronomical factors align. The exact dates vary year to year because the lunar perigee and spring tides don't align on a fixed schedule. Some years see more pronounced king tides than others. NOAA and other agencies publish predicted king tide dates years in advance, since the astronomical alignments are fully predictable.
Why do king tides matter for sea level rise?
King tides have become important for studying sea level rise impacts. Today's king tides preview what average daily tides will look like in coming decades as oceans continue rising. Coastal communities use king tide events to identify vulnerable areas, document flooding patterns, and plan adaptation. Citizen science programs encourage people to photograph and report king tide flooding. The visual evidence helps demonstrate sea level rise impacts in concrete terms, since the same flooding that occurs only at king tides today will occur much more frequently in the future.
A king tide is the highest predicted high tide of the year, occurring when spring tides coincide with the moon's closest approach to Earth (perigee). They cause exceptionally high water levels several times each year, sometimes flooding low-lying areas. King tides have become important as previews of sea level rise impacts, demonstrating how rising baseline ocean levels will affect coasts in the coming decades.
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