Definition
LAT is the lowest predicted level under any combination of astronomical conditions and average meteorological conditions, derived from analysis of at least 19 years of predictions to cover the lunar nodal cycle. Adopted by the IHO as the standard chart datum, it guarantees that predicted heights of tide are almost always positive. Meteorological effects such as high barometric pressure and strong offshore wind can still take the actual level below LAT, occasionally by half a metre or more.
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