Tide heights are the result of –
(1) astronomical effects, which can be predicted
(2) meteorological effects which can not be predicted.
Astronomical – Spring tides are nothing to do with the Spring season. Each month has two spring tides – at full moon and at new moon. The moon is the main influence on the height of high water. The sun also has an effect but it is much less than the moon. Twice every year, around each equinox, the alignment of the sun and moon causes a stronger than normal influence on the tides – for 2012 these dates are 10th March (high water predicted to be 9.98 metres above Chart Datum) and 16th October (predicted to be 10 metres above CD). (A particularly high water of 10.37 metres is predicted on 29th September 2015.)
Meteorological – air pressure, wind direction and wind speed have a significant effect on water height. The bird-watchers who gather at Parkgate on the dates shown above will hope for low air pressure combined with a strong westerly wind. An exceptional storm surge on 27th October 2002 added 2.26 metres to the water height locally.
How much difference does one metre of tide height make? A typical high water of 8.5 metres floods the nineteen miles from Hilbre Island to the weir at Chester.
At Parkgate, silting has raised the marshland height above the estuary sands. Nevertheless, a combination of astronomical and meteorological influences still has the potential to cause the water to breach the sea wall.
Lots of information
here and on that website’s other pages.