King Tide
Also called: perigean spring tide
King tide is a popular, non-scientific name for an exceptionally high tide. King tides happen when the higher tides around a new or full moon coincide with the Moon's closest approach to Earth, called perigee. They can flood low-lying coastal areas on a clear day, and they raise the water level any storm surge is added to.
Key Points
- The scientific name for the cause is a perigean spring tide. Spring tides, the higher tides around each new and full moon, have nothing to do with the season.
- Flooding from high tides alone is called high tide flooding, also known as sunny day or nuisance flooding. NOAA counts it as minor once the water is about 1.8 feet above the average high tide.
- High tide flooding is now twice as frequent in U.S. coastal communities as it was 20 years ago, as sea level rises.
- A storm that arrives during a king tide produces a higher storm tide, because storm tide is the surge plus the astronomical tide.
Related Terms
Storm Surge
Storm surge is an abnormal rise in sea level during a hurricane or other intense storm, measured as the height of the water above the normal predicted tide. It is produced mainly by the storm's winds pushing water toward the shore. Storm surge is the leading cause of deaths from hurricanes.
Rip Current
A rip current is a strong, narrow channel of water flowing away from the beach through the surf zone. Rip currents can form on any beach with breaking waves, including the Great Lakes, and can reach 8 feet per second, faster than an Olympic swimmer. They carry swimmers away from shore, not under the water.
Small Craft Advisory
A Small Craft Advisory is a National Weather Service alert for winds or seas that are hazardous to small boats in coastal and Great Lakes waters. The wind and sea thresholds are set separately for each geographic area. There is no precise definition of a small craft: any vessel that the conditions could affect counts.
Hurricane
A tropical cyclone with maximum one-minute sustained surface winds of 74 mph or greater in the Atlantic or eastern and central North Pacific. Hurricanes are categorized 1-5 on the Saffir-Simpson Hurricane Wind Scale, with Category 5 beginning at 157 mph.
Nor'easter
A storm along the East Coast with winds blowing from the northeast. Nor'easters can bring heavy snow, rain, and coastal flooding, especially from Virginia to New England. The most powerful nor'easters rival hurricanes in intensity.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Tool
Moon Phase Calculator
Check the lunar phase and illumination for any date, past, present, or future.
Guide
GFS vs HRRR vs NAM
Learn which forecast model to trust for different situations and how to interpret model data.
Feature
Conversational AI
Ask about rain timing, alerts, and what the forecast means in plain language.
Guide
How to Read Weather Radar
Learn the basics of radar interpretation so you can tell where storms are headed and how intense they may become.
Sources
Explore Other Terms
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
Liquefaction
A process in which water-saturated, loosely packed soil temporarily behaves like a liquid during strong shaking and loses its ability to bear weight. It can tilt or sink buildings, float buried tanks and pipes upward, and cause the ground to crack and spread sideways. Reclaimed land, river deltas, and sandy fill are especially vulnerable.
Tornado
A tornado is a violently rotating column of air in contact with the ground, extending from a thunderstorm. Tornadoes are rated from EF0 to EF5 on the Enhanced Fujita scale by the damage they cause. Most last less than 10 minutes, but the strongest can stay on the ground for more than an hour.
Thundersnow
A rare phenomenon where thunder and lightning occur during a snowstorm. Thundersnow typically happens in intense winter storms and is often associated with heavy snowfall rates of 2-4 inches per hour.
Heat Index
The heat index is how hot it feels when relative humidity is combined with the air temperature. Humid air slows the evaporation of sweat, so the body cools less efficiently and feels hotter than the thermometer reads. At 100°F with 55% relative humidity, the heat index is 124°F.
Velocity
Doppler radar measurement of how fast precipitation is moving toward or away from the radar. Velocity data reveals wind patterns, rotation in thunderstorms, and potential tornado signatures that reflectivity alone cannot show.
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