US Trends

what causes king tides

King tides are caused by an extra-strong combination of gravitational pulls from the Moon and Sun, plus the Moon and Earth being at their closest points in orbit, which together create the highest tides of the year.

What king tides are

  • King tides are not a special new kind of tide, but the highest naturally occurring high tides in a year.
  • They are predictable and follow astronomical cycles, so scientists can forecast them years in advance.

Core causes of king tides

  • Alignment of Earth, Moon, and Sun (new or full moon) creates “spring tides,” when high tides are higher and low tides are lower than average.
  • When this alignment happens at the same time the Moon is at perigee (its closest point to Earth), the lunar gravitational pull on the oceans is strongest, producing perigean spring tides, commonly called king tides.
  • The Earth is also slightly closer to the Sun around early January (perihelion), which marginally boosts the Sun’s tidal effect and can help make the year’s very highest king tides then.

Other factors that make them higher

  • Local weather can “stack” extra water on top of a king tide: low-pressure systems, strong onshore winds, and large ocean swell can raise water levels beyond the astronomical prediction.
  • Coastal shape and depth (bays, estuaries, harbors) can amplify the height of a king tide in some locations compared with the open coast nearby.

King tides and sea-level rise

  • King tides themselves are natural, but they now ride on top of a higher average sea level because of human‑driven climate change and ocean warming.
  • That means today’s king tides increasingly cause “sunny‑day” or nuisance flooding in low‑lying neighborhoods and give a preview of what everyday high tide could look like as sea level continues to rise.

Why they matter for coasts

  • During king tides, flooding can affect roads, basements, storm drains, and shoreline infrastructure, especially if a storm or big waves occur at the same time.
  • Communities and scientists use king tide days to photograph and map flooded areas, helping plan future defenses and adaptation to higher seas.

TL;DR: King tides happen when the Moon and Sun line up with Earth during a new or full moon, the Moon is unusually close to Earth, and sometimes Earth is near its closest point to the Sun; local weather and rising sea levels can make these already extreme high tides even more impactful along coasts.