The tidal force produced by the moon's gravitational attraction is accompanied by a tidal force of considerably smaller amplitude produced by the sun. The position of this tidal force shifts with the relative orbital position of the earth in respect to the sun. Since the resultant or combined tidal force is also increased, the observed high tides and higher and low tides are lower than average. This means that the tidal range is greater at all locations which display a consecutive high and low water. Each force tends in part to counteract the other.
High tides are lower and low tides are higher than average.
The inflowing, or high tides, are also called flood tides, while the outgoing, or low tides are called ebb tides. The movement of the sun and moon are known so we can predict the tides and rely on those predictions in the oceans, but other factors are necessary to consider when predicting the tides of estuaries. The shape of the estuary's shoreline and bottom can have a dramatic affect on tides. The opening of an estuary is narrow and restricts movement in and out. Weather can also have a dramatic effect on tidal predictions, particularly in a broad, shallow estuary such as the Chesapeake Bay.