What is a king tide?
A king tide is the informal name for the highest tides of the year. The term is not scientific, but the event is: oceanographers call them perigean spring tides, and they arrive on a schedule set entirely by the sun and moon. If you have ever seen a harbor parking lot go underwater on a clear, windless day, you have probably seen a king tide at work.
The astronomy behind it
Every new and full moon brings spring tides, when the sun and moon pull in line and the tidal range grows. The moon’s orbit is also slightly oval, so once a month it swings closest to Earth at a point called perigee. When a new or full moon lands within a day or so of perigee, the two effects stack and the range grows further still. Those few days are the king tides, typically a handful of times per year. The background rhythm is covered in our guide to spring vs neap tides.
Sunny day flooding
Because king tides are the year’s highest water, they are also a preview of the future coastline. Low streets, docks, and storm drains that stay dry the rest of the year can flood for an hour or two around the peak, with no storm in sight. Coastal agencies use king tide photo projects to map where rising seas will reach first. If you live or park near the water, it is worth knowing the dates before the water finds your floor mats.
The other side: epic low tides
Every extreme high comes paired with an extreme low six hours or so away. King tide lows expose rocks, flats, and tidepools that are underwater almost all year, which makes these some of the best days on the calendar for tidepooling, clamming, and shoreline photography. If that is your goal, see our guide to minus tides, clamming, and tidepooling for how to plan the walk.
A note on safety
King tides deserve mild respect. The water rises and falls through a bigger range in the same six hours, so currents run stronger than usual and the flood can cut off a beach or sandbar faster than you expect. Give low-lying paths extra margin, keep an eye on the time near the turn, and remember that wind and low pressure can push the real water level above the prediction.
Find the next one in Slackwater
The Slackwater app computes the full tide curve for your station on your device from NOAA harmonic data, so the year’s biggest highs and lowest lows stand out as soon as you scroll ahead. Check tide times by location to see when the next king tide reaches your stretch of coast.
Common questions
When do king tides happen?
A few times a year, when a new or full moon coincides with perigee, the moon's closest approach to Earth. On much of the US coast they cluster in late fall and winter, but the exact dates vary by year and location.
Are king tides caused by climate change?
No, they are ordinary astronomy, the same forces that make every spring tide. But sea level rise makes each year's king tides reach a little farther inland, which is why they are used as a preview of future flooding.
How much higher is a king tide than a normal high tide?
Often a foot or two above an average high, depending on the location's tidal range. Local weather can add more: onshore wind and low pressure can push a king tide well past its predicted height.