# What is a perigean spring tide?

> A perigean spring tide occurs when a new or full moon falls close to perigee, the moon's nearest point to Earth in its monthly orbit. The alignment of the sun, Earth and moon produces a spring tide, while the moon's closer distance...

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Published: 2026-08-28T13:37:00+00:00
Categories: Explainer, Oceans

![A serene full moon rising over peaceful waters and lush landscape in Eastern Visayas, Philippines](https://www.argo.net/wp-content/uploads/2026/08/moon_over_high_tide.jpg)

A **perigean spring tide** occurs when a new or full moon falls close to perigee, the moon's nearest point to Earth in its monthly orbit. The alignment of the sun, Earth and moon produces a spring tide, while the moon's closer distance strengthens its tide-producing effect. High water is generally higher and low water lower than during many other tides.

NOAA's [perigean tide explanation](https://oceanservice.noaa.gov/facts/perigean-spring-tide.html) says the combination typically happens six to eight times a year. The precise increase varies greatly by location because coastlines and seafloor depth control how the astronomical forcing appears at a harbor or beach.

## Spring tide describes alignment

The moon's gravity supplies most of Earth's tide-producing force and the sun contributes as well. During a new moon, the moon lies roughly between Earth and the sun. During a full moon, Earth lies roughly between them. In either arrangement, the sun's and moon's effects reinforce one another.

The result is a larger **tidal range**, the difference between high and low water. High tides tend to rise above average, while low tides fall below average. These are spring tides, named for the water's upward springing. They occur twice during the roughly 29.5-day cycle of lunar phases and are unrelated to the season called spring.

Near the quarter moons, the sun and moon pull at roughly right angles relative to Earth. Their tide-producing effects partly counter one another, creating a smaller range called a *neap tide*. Comparing spring and neap tides explains the alignment part of a perigean spring tide, but distance supplies the second ingredient. Alignment also affects low water, so the phenomenon is best understood through the full range rather than the height of one high tide. A larger predicted range can expose more mudflat or reef at low water before the higher high arrives. The greater vertical change can also affect clearance beneath a vessel in shallow water. Low-water hazards can therefore become more exposed during the same cycle. Local tide tables show both stages and keep the comparison tied to one station and one **vertical datum**.

## Perigee adds the distance effect

The moon's orbit is elliptical, so its distance from Earth changes. Perigee is the closest point of one orbit, reached about once every 28 days. Roughly two weeks later, the moon reaches apogee, its farthest point. The moon produces a somewhat larger tidal range near perigee and a smaller one near apogee.

When perigee and a full or new moon occur close together, their influences combine. The popular phrase **supermoon** is often applied to a full moon near perigee, while perigean spring tide refers directly to the water response and also includes new moons. The moon does not need to be at its exact minimum distance at the exact instant of lunar alignment for the label to be useful.

NOAA's [tide FAQ](https://tidesandcurrents.noaa.gov/faq.html) notes that high tides during a perigean spring tide can exceed those during an apogean spring tide by more than a foot in some places. Anchorage, with a tidal range exceeding 30 feet, can see a difference of three feet or more. Such figures illustrate local amplification rather than a universal increase.

Perigee occurs once in each orbit, but its date does not stay locked to a lunar phase. The interval between phases and the interval between successive perigees differ slightly, so the two cycles drift into and out of close timing. NASA's account of the [Moon's orbit](https://science.nasa.gov/moon/facts/) also shows why its distance varies continuously. "Close to perigee" describes a window, rather than one universal cutoff used by every forecast office.

## Why the height varies by coast

Astronomical forcing crosses an ocean whose basins have irregular shapes and depths. Continents interrupt the ideal tide wave. Shelves and bays alter its timing and height, as do inlets. Some coasts have a single high tide each day, many have two similar highs and others have two unequal highs. The perigean effect is superimposed on each local pattern.

Seasonal mean water level can raise or lower the baseline. Warmer water expands, winds change and ocean currents shift. Along the U.S. East and Gulf coasts, seasonal water levels often peak in late summer or early fall. On the West Coast, solar declination helps produce larger perigean spring-tide ranges near the summer and winter solstices.

Weather determines the observed water level around the prediction. Onshore wind and low pressure can add water, while offshore wind may reduce it. Waves create runup beyond the still-water tide. A tide-table value should therefore be read alongside marine and coastal flood forecasts, particularly when the predicted high approaches a known impact elevation.

Tide gauges separate prediction from observation. The prediction represents the expected astronomical components at the station, while the measured trace includes weather and broader ocean conditions. Comparing the two helps forecasters see whether water is already running high before the perigean peak. It also prevents a weather-driven residual from being attributed entirely to the Moon.

## When flooding can occur

Many perigean spring tides pass without flooding. Dry land remains dry when the highest observed water stays below local thresholds. Low-lying areas become vulnerable when the astronomical high combines with elevated seasonal water, wind, currents, waves, or rising relative sea level.

When water crosses onto normally dry land during high tide, agencies call the impact **high-tide flooding**. A storm surge is a different rise generated mainly by storm winds, although it can overlap the same tide. Starting a storm surge from a perigean high tide can worsen the final reach or depth of flooding.

Rising relative sea level narrows the vertical gap between high water and streets. The astronomical cycle continues, but more of its peaks can cross fixed elevations. NOAA's [monthly outlook](https://tidesandcurrents.noaa.gov/high-tide-flooding/monthly-outlook.html) identifies dates when above-normal tides may contribute to local flooding, incorporating predicted astronomical conditions.

The same predicted tide can therefore have a different impact decades apart. A threshold that once stood safely above every astronomical peak may later be crossed during calm weather. Land subsidence can accelerate the local change, while uplift can offset part of the ocean rise. The relevant quantity for residents is **relative sea level** at the coast.

## How to check the next event

Use an official tide station near the place of interest. NOAA's [tide predictions](https://tidesandcurrents.noaa.gov/noaatidepredictions.html) list the time and height of high and low waters. Confirm the station, time zone and vertical datum. A prediction from an exposed coast may not match a river, inlet, or harbor only a short distance away.

Look at the predicted peak in relation to local flood thresholds, then check wind, wave and rainfall forecasts. Coastal alerts account for conditions that a long-range astronomical table cannot. Boaters also need current predictions because a large tidal range can produce strong flows in narrow passages and the time of maximum current may differ from high or low water.

Beach visitors should expect less dry sand at high tide and possible loss of access around rocks or headlands. View the event from stable ground, away from wave-washed surfaces. A perigean spring tide is predictable astronomy interacting with a specific coast; safe observation depends on the weather and terrain present that day.

Prediction times also require care away from the reference station. A subordinate location may peak earlier or later and narrow channels can carry strong **tidal currents** after the listed high or low water. Local current tables are the better tool for passage planning. The tide-height table alone cannot identify slack water safely.

**Related reading:** [how ocean waves form](https://www.argo.net/how-do-ocean-waves-form/) and [spring tides and neap tides](https://www.argo.net/spring-tide-vs-neap-tide-what-is-the-difference/).

 **Explore this topic:** [What is high-tide flooding?](https://www.argo.net/what-is-high-tide-flooding/) and [What is a meteotsunami?](https://www.argo.net/what-is-a-meteotsunami/).