Why is the actual water level different from the tide chart?

The chart predicts the astronomical tide, while the observation also includes wind, atmospheric pressure, runoff, waves, and other local effects.

What is a water-level residual?

It is the observed water level minus the predicted tide at the same station, time, units, and datum.

Wind can raise or lower observed coastal water, but the amount depends on duration, direction, basin shape, depth, and shoreline orientation.

Tide is the regular astronomical rise and fall. Storm surge is an abnormal storm-driven rise above the predicted astronomical level.

Not necessarily. The prediction is an astronomical baseline; the observation records additional real-world influences.

Use prediction for planning, then check observations and official warnings close to the event. Emergency guidance always takes priority.

Compare astronomical tide predictions with observed water levels, including how wind, pressure, runoff, and storms can raise or lower coastal water.