King Tides and High Tide Flooding: Why Sunny-Day Floods Happen and How NOAA Measures Them
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How we wrote this: A plain-English summary of NOAA National Ocean Service pages on king tides and high tide flooding, checked October 29, 2026. For flood warnings, follow your local National Weather Service office.
Coastal streets can flood on a cloudless day. NOAA explains why.
What a king tide is
NOAA says "king tide" is a popular, non-scientific term for exceptionally high tides. Tides are long waves pushed around the planet by the gravitational pull of the moon and the sun. Higher-than-normal tides typically occur during a new or full moon, and when the moon is at perigee, its closest point to Earth. (A full moon at perigee is a supermoon.)
What high tide flooding is
NOAA uses "high tide flooding" (sometimes called sunny day or nuisance flooding) for flooding that happens when sea level rise combines with local factors to push water above the normal high tide mark. No storm is needed. Contributing factors include:
- changes in prevailing winds,
- shifts in ocean currents,
- strong tidal forces during full or new moons,
- sinking land (subsidence) and the loss of natural barriers.
NOAA's three severity levels
Measured as water above a location's average high tide:
| Level | Height above average high tide | Typical effects |
|---|---|---|
| Minor | 0.55 m (1.8 ft) | Mostly disruptive: stormwater backups, road closures |
| Moderate | 0.85 m (2.8 ft) | More disruption, can damage homes and businesses |
| Major | 1.20 m (3.9 ft) | Destructive. May lead to evacuations and infrastructure repairs |
It's getting more common
NOAA says high tide flooding is now twice as frequent in U.S. coastal communities as it was 20 years ago, and it has increased especially along the East Coast.
Planning a beach day or a coastal drive
- Check tide predictions for the nearest station (see how to read a tide chart), and watch for unusually high values around new and full moons.
- NOAA publishes a monthly high tide flooding outlook and a Sea Level Rise Viewer.
- Don't drive through flooded streets. Salt water is also hard on cars.
See also: tsunami safety, moon phases, hurricane categories.