The average speeds are then between 0.5 and 1.0 knots up to the head of the Bay. There are two kinds of tidal cycles in the Bay. In the southern Bay and in Tangier Sound, the tides and tidal currents are semidiurnal while in the central and northern Bay, they are classified as mixed. Semidiurnal tides generally have two high and two low waters each day. Diurnal tides generally have one high and one low per day.
Mixed tides are a combination of semidiurnal and diurnal tide types.
A characteristic of mixed tides is that on days when two high waters and two low waters occur, the two high tides and the two low tides will be of unequal height. The tides and tidal currents in the Bay described above can be significantly modified by the effects of local and large scale meteorological patterns. These effects include strength and duration of wind speed and direction, barometric pressure changes, and river runoff. The tides in the Bay are highly susceptible to modification because the Bay is generally shallow and the tides and the tidal current are very weak. The effect on the tides is highly dependent on the direction of the winds relative to the orientation of the basin, and the scale of the meteorological event.