What is left after the astronomical prediction is subtracted from the observed record. Residuals carry storm surge and set-down, pressure effects, river floods, seasonal changes and any sensor or datum problems. Forecasters track the residual to warn of flooding, and analysts check it after harmonic work: a residual that still shows a tidal rhythm means the analysis missed something.
Residual's been plus 0.4 all day with the onshore wind, so tonight's high will top the prediction by about that.
Also heard as
- non-tidal residual
- surge residual
- anomaly
Related terms
Storm surge
A rise of water above the predicted tide caused by a storm's winds and low pressure.
Astronomical tide
The part of the water level caused only by the gravitational effects of the Moon and Sun.
Tidal prediction
A forecast of tide heights or currents computed from harmonic constants and astronomy, with no weather included.
Set-down
A drop in water level below the predicted tide caused by winds blowing water away from the coast.