Fallen, broken tree in a park. Credit: RenegadeStudio

Severe Atlantic storm batters Ireland and UK

9 December 2014 16:00 UTC–10 December 06:00 UTC

Fallen, broken tree in a park. Credit: RenegadeStudio
Fallen, broken tree in a park. Credit: RenegadeStudio

A very deep area of low pressure resulted in a North Atlantic cyclone (named Alexandra) which caused massive ocean surges and brought strong winds to parts of Ireland and the UK in December 2014.

Last Updated

06 September 2022

Published on

09 December 2014

Gale force gusts of more than 129km/h (80mph) were recorded at Tiree in Scotland and ocean waves over 15m (50ft) high were recorded by the K5 buoy off the north west coast of Scotland (59.10N, 11.40W).

The strong winds caused transport chaos and power outages across the northern parts of the UK.

Meteosat-10 Airmass RGB showing the cyclone over the North Atlantic, 9 December 16:00 UTC
Figure 1: Meteosat-10 Airmass RGB showing the cyclone over North Atlantic, 9 December 16:00 UTC

The gales and ocean surges were caused by rapid or explosive cyclogenesis — an intense low pressure system with a central pressure that falls 24hPa in a 24-hour period, referred to colloquially as a 'weather bomb'.

In his weather blog, ITV weather forecaster Liam Dutton explained how the jet stream caused the cyclogenesis.

Download full resolution RGB image, Meteosat-10 Airmass RGB, 9 December 16:00 UTC
Download animation, Meteosat-10 Airmass RGB, 8 December 10:00 UTC–11 December 10:00 UTC

The Airmass RGB image from 9 December 12:00 UTC (left side) shows the system had a central pressure of less than 950hPa. The ASCAT instrument on Metop measured 60 knots (111km/h), but the real winds were probably higher as ASCAT winds saturate at around 60 knots (higher winds than 60 knots do not produce a higher ASCAT signal).

Also striking in this image are the strong winds over the Western Mediterranean caused by Mistral winds (two storms caught in one image).

The Airmass RGB image from 10 December 06:00 UTC (right side) shows the very large fetch zone of the storm, which is ideal (conditions) for forming high (monster) waves and very large ocean surge.

Met-10/Metop-B, 09 December 2014, 12:00 UTC
Figure 2: Meteosat-10 Airmass RGB with Metop-B ASCAT winds and surface pressure overlaid, 9 December, 12:00 UTC. Credit: EUMeTrain.
 
Met-10, 10 December 2014, 06:00 UTC
Figure 3: Meteosat-10 Airmass RGB with 10m ECMWF model winds, 10 December 06:00 UTC. Credit: EUMeTrain
 
Plot of significant wave heights over the Atlantic
Figure 4: Plot of significant wave heights over the Atlantic

The plot (right) shows the significant wave height in the Atlantic recorded by SARAL/Altika and Jason-2 satellite altimeter passes from 15:00 UTC to 21:00 UTC on 9 December.

The colour scale ranges from 0 to 20m, with the areas coloured in orange, brown and red showing significant wave heights of more than 10m. Significant wave height is defined as the mean height of the biggest third of all the waves.


Additional content

'Weather Bomb' - Explosive Cyclogenesis in the Atlantic , video of EUMETSAT infrared imagery (YouTube)
A closer look at ‘weather bombs’ (Met Office)
'Weather bomb' hits power and travel in northern UK (BBC News)
Huge waves crash on Orkney Islands (BBC News)