Lowest Astronomical Tide (LAT)

The lowest level that sea tides can reach under normal meteorological conditions, based on astronomical influences such as the gravitational pull of the moon and sun.

Lowest Astronomical Tide (LAT) is a tidal datum used as a reference point for charting and navigation. It represents the lowest predicted tide level that can occur due to the gravitational forces of celestial bodies, primarily the moon and the sun, without considering meteorological factors like wind or atmospheric pressure. LAT is essential for mariners because it provides a conservative estimate of the minimum water depth that can be expected in a given area under typical astronomical conditions. This ensures that vessels can navigate safely, knowing the water depth will not fall below this level, barring unusual weather events.

LAT is determined through long-term observations and predictions of tidal patterns, often spanning many years, to account for the full range of tidal variations. It is used as a standard reference for depth soundings on nautical charts, meaning that all depths shown are often measured relative to this lowest point. This allows mariners to calculate how much water will be beneath their vessel at any given time based on the current tide level. LAT is particularly useful in areas with significant tidal ranges, where the difference between high and low water levels can be substantial. Using LAT as a baseline, mariners can avoid grounding and ensure safe passage through shallow waters.