Storm observations – Record 21.48 metre waves

Over the last few days, we have experienced the first major winter storm with gusts of up to 69 knots (80mph) and waves reaching a massive 21.48 metres (that’s 70.5 feet). The amber wind warnings were out with the public advised to “be prepared” though from many reports online, people didn’t bother, and paid the cost.

In Portstewart, Co. Londonderry, a jogger and a dog-walker were overcome with waves while walking on the beach, but managed to clamber ashore. Other incidents with outside furniture being blown into windows, trampolines and other loose debris becoming a serious safety hazard to anyone in their path, all demonstrate how these warnings should be taken seriously.

Before the online data disappears into a computer somewhere, I thought I would put some of the available weather recordings together and let you see the wave height and atmospheric pressure comparison that show how this rapid change in pressure caused such voluminous waves to occur.

We also seen a term not often used in the shipping forecast to describe sea state.


“Phenomenal” describes a wave height of over 14 metres. The term comes from Captain H.P. Douglas, a hydrographer in the Royal Navy in the 1920s. To find out more, you can read about him on Wikipedia.

Another sexy weather term has also appeared during the build up to this storm. A weather bomb! A “weather bomb” is an explosive cyclogenesis, when a storm intensifies as the pressure at its centre drops rapidly by more than 24 millibars in 24 hours.

The meteorological phenomena known as rapid or explosive cyclogenesis occurs when dry air from the stratosphere flows into an area of low pressure. It is a rare event which almost always happens at sea with the North Atlantic having the right conditions for it.

For more information, visit the Met. Office website.

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