Spring tides contributed to Thursday's storm surge at coast

Bare - Chris Coates Photo:

At the new moon the tide is at its maximum range. This is called a 'Spring tide'. The daily high tide (around lunchtime) combined with today's strong north westerly winds pushed water down the Irish sea causing waves to pile over sea walls.

Low pressure and Atlantic storm

A storm surge is a very localised rising of sea level - independent of tides - related to the track of a storm and its accompanying winds.

The storm causes this surge of water in two ways. Firstly strong winds, often blowing parallel to the coast or onshore, push water roughly in their direction which causes water to 'pile up' on nearby coasts.

The second element, which is less important for the UK, relates to differences in air pressure. Low pressure, associated with storms, exerts less of a force on the sea surface - allowing the sea surface to temporarily rise in the vicinity of low pressure.

Local geography also plays a role. North Sea areas are particularly prone to storm surges because water flowing into the shallower southern end cannot escape quickly through the narrow Dover Strait and the English Channel. The shallow depths in the southern North Sea also aid the development of a large surge.

When storm surges combine with high tides, especially spring tides, and large waves they can cause flooding issues along coasts.