A STORM surge is a change in sea level caused by bad weather.

The main cause of a storm surge is high winds pushing the sea water towards the coast, causing it to pile up.

There is also a smaller contribution from the low pressure at the centre of the storm "pulling" the water level up, by about one cm for every one millibar change in pressure.

This is called the inverse barometer effect, and is similar to what happens when drinking through a straw.

The strong winds in the storm generate large waves on top of the surge which can cause damage to sea defences, or spill over the top adding to the flood risk.