Q. How are tides predicted?
First the behaviour of the tide has to be recorded by a tidegauge at each particular location and the observations subsequently analysed. The results of these analyses, known as tidal constants, are then used in a computer program to predict the behaviour of the tide for any period required.
Q. How far ahead can the tide be predicted?
The tides are generated by gravitational influences of the Earth-Moon-Sun system, whose astronomical relationship and orbital details are known extremely accurately. Using this information, together with the tidal constants derived from the tidal analyses, the tides can be predicted for any date as far ahead into the future as required.
However, for predictions well into the future (many decades) the effects of global sea level rises and changes in seabed topography have to be carefully considered. These may have a significant effect upon local tidal behaviour, and the predictions can only be computed using the tidal data currently available on the UKHO database. So the further ahead we go from the date the tidal data is held on the database, the less reliable the predictions will become.
Q. What are "Spring" and "Neap" tides?
Spring and Neap tides are created by the relationship between the Earth and the Moon during each lunar month. Spring tides occur shortly after New and Full Moon, and Neap tides occur shortly after the Moon is in its First and Third Quarter.
Spring tides occur when the gravitational forces of the Sun and Moon reinforce each other resulting in a higher than normal tidal range. Neap tides occur when these gravitational forces act at right angles to each other resulting in a lower than normal tidal range. Spring tides are nothing to do with the season, but it is believed the name is derived from a medieval word to "leap up". Neap comes from an old English word for "low" or "to nip".
Q. When can we expect the largest spring tides each year?
The largest spring tides occur in this country shortly after the New and Full Moon closest to the equinoxes, and are sometimes referred to as "Equinoctial Spring Tides". The spring (or vernal) equinox occurs around 21st March, and the autumnal equinox occurs around 23rd September
USE THE LINKS BELOW TO FIND OUT TIDE HEIGHTS
River Foyle - Culmore Point - Londonderry - Coleraine