A king tide is the highest predicted tide of the year — an exceptionally large spring tide that occurs when the new or full moon coincides with the moon's closest approach to Earth (called perigee). On the Outer Banks, king tides push ocean levels 15 to 20% higher than an average spring tide. Combined with onshore wind, even a moderate northeast blow can flood Highway 12, overwash Pea Island, and inundate low-lying neighborhoods on Ocracoke and Hatteras Island.

What makes a king tide

Three astronomical factors stack up to produce a king tide:

• Spring tide alignment. Sun and moon pull in the same line (new moon or full moon), reinforcing each other's gravitational tug on the ocean.
• Lunar perigee. The moon orbits Earth in an ellipse. At perigee — about every 27.5 days — it sits roughly 14% closer than at apogee. Closer moon = stronger pull.
• Seasonal sea level peak. On the OBX, sea level naturally runs 6 to 10 inches higher in September and October than in spring, due to thermal expansion of the water column and persistent onshore winds. See our seasonal sea level page.

When all three line up — a perigean full or new moon during the autumn peak — you get the biggest astronomical tide of the year. The next layer is wind: a sustained northeast blow can add another foot or two of storm surge on top of the king tide.

When OBX king tides happen

King tides are predictable years in advance because they're purely astronomical. The most flood-prone OBX king tides typically hit:

• September–October: Autumn perigean spring tides, when seasonal sea level is already high. This is the worst flooding window of the year.
• November: A second autumn peak as the moon stays near perigee.
• March–April: Spring equinox king tides, generally less destructive because seasonal sea level is lower.

NOAA publishes annual king tide calendars on its tides and currents site. For OBX-specific timing, check the predictions for Duck and Hatteras and look for tide heights at or above 4.0 ft (Duck) or 1.8 ft (Hatteras) — those are well above normal spring tide highs.

Where king tides flood on the OBX

• Highway 12 on Pea Island — overwash sections regularly close to traffic
• S-Curves north of Rodanthe — historic flooding hotspot
• Mirlo Beach (Rodanthe) — ocean breaches into Pamlico Sound
• Buxton beachfront — narrow dune line allows easy overwash
• Ocracoke Village — Silver Lake Harbor and lower NC-12 inundate
• Manteo waterfront — sound side flooding from wind setup
• Kitty Hawk beach road — northern OBX overwash zone

King tide vs storm surge

A king tide is purely astronomical and is predictable. Storm surge is the wind- and pressure-driven extra rise during a tropical or extra-tropical storm and is much less predictable. The dangerous combination is a king tide arriving while a nor'easter or hurricane is offshore. The astronomical high gives the storm surge a “running start” — water that would normally crest at 3.5 ft might crest at 6 or 7 ft. The storms & nor'easters page covers storm surge in depth.

How to plan around king tides

• Check the annual king tide schedule before booking shoulder-season OBX trips
• Avoid driving Highway 12 on Pea Island within 90 minutes of a king tide high water
• For beach driving, expect NPS to pre-emptively close ramps in flood-prone zones
• Surf fishermen: king tide highs push bait into normally dry zones — sometimes producing exceptional bite windows just before and after the peak
• Sign up for Dare County and Hyde County emergency alerts

Related

• Moon phase & tide calendar
• Seasonal sea level on the OBX
• Storms & nor'easters: storm surge
• OBX tide charts by location

King tides and rising baseline

See OBX Sea Level Rise & King Tides for how rising mean water at the Duck NC gauge is reshaping which streets flood during the highest predicted tides each year.