Thursday, December 11, 2014

Severe North Atlantic cyclone strikes Ireland and UK

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.

Met-10/Metop-B, 09 December 2014, 12:00 UTC 

Airmass RGB, with surface pressure and ASCAT winds 

Credit: EUMeTrain

Gale force gusts of more than 129 km/h (80 mph) were recorded at Tiree in Scotland and ocean waves over 15 m (50 ft) 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 outtages across the Northern parts of the UK.

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

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

The Airmass RGB image from 9 December 12:00 UTC (left side) shows the system had a central pressure of less than 950 hPa.

Met-10, 10 December 2014, 06:00 UTC.

Airmass RGB with 10 m ECMWF model winds 

Credit: EUMeTrain

The ASCAT instrument on Metop measured 60 knots (111 km/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.

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