Why the Ocean Has Waves, and the Difference Between Storm Surge and Storm Tide
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How we wrote this: A plain-English summary of NOAA National Ocean Service explainers on waves and storm surge, checked October 29, 2026. In a storm, follow your local officials and the National Weather Service.
How waves form
NOAA says waves are energy passing through water, which makes the water move in a circular motion. The key point is that waves move energy, not water. Unobstructed, a wave can cross an entire ocean basin.
- Wind waves (surface waves) are the everyday kind, made by friction between wind and water.
- Tides are waves too, very long ones driven by the moon and sun (see spring and neap tides).
- Tsunamis come from earthquakes, landslides or volcanic eruptions that suddenly displace water. NOAA notes it's a misconception that a "tidal wave" is a tsunami. Tsunamis aren't related to tides and can happen at any tide. See tsunami safety.
Storm surge vs. storm tide
NOAA says that in a hurricane, the greatest threat to life comes from the water.
| Term | NOAA definition |
|---|---|
| Storm surge | The abnormal rise in sea level caused solely by a storm, measured above the normal predicted tide. It's driven mainly by the storm's winds pushing water onshore. |
| Storm tide | The total observed water level during a storm, meaning storm surge plus the normal astronomical tide. |
How big a surge gets depends on the storm's intensity, size, speed and track relative to the coast, and on the shape of the sea floor nearby. Because tides peak around new and full moons, NOAA notes the highest storm tides often come when a storm coincides with a new or full moon.
What it means at the beach
- A forecast "surge of 6 feet" is on top of the tide, so timing with high tide matters.
- Big surf from a distant storm can reach beaches on sunny days, often with dangerous rip currents.
- See hurricane categories and beach warning flags.