Extreme Waves in the Celtic Sea and the English Channel on 14-15 February 2014 Dr

Extreme waves in the Celtic Sea and the English Channel on 14-15 February 2014 Dr. Susanne Haeseler; updated: 27 February 2014

Introduction

During the last several weeks, strong storms frequently formed across the North Atlantic, moving in a westerly flow across north-western Europe. Several of these developed to storms of hurricane force with a central pressure ≤ 950 hPa: seven in December 2013, six in January 2014, and three in February 2014. Since records began in 1956, this high number of 16 hurricane force storms during winter months was only observed in the winter of 1990/1991, followed by15 in the winter of 1989/1990 and by 14 in the winter of 1992/1993.

Several of the recent storms have taken a more southerly track than usual, especially in Jan- uary and February 2014, badly affecting the British Isles. Much damage was caused by strong winds with hurricane force gusts, by high water levels and floods due to frequent and heavy precipitation associated with the storms, as well as by high seas along the coasts.

Not only people on land were endangered by high seas but also ships at sea. The strength of the waves caused damage even on big ships such as the cruise ship MS Marco Polo. The shipping company reported that MS Marco Polo was hit by a freak wave in the area of the Celtic Sea in the afternoon of 14 February 2014 en route from the Azores to Tilbury (a har- bour near the Thames estuary in England) (statement on 14 February 2014, statement on 15 February 2014). The wave smashed the windows of an on-board restaurant on deck 6. One passenger died, several others sustained injuries. The property damage was limited to a small section of the restaurant (statement on 16 February 2014).

Weather conditions and sea state on 14 February 2014, Celtic Sea

On 14 February 2014 at 12 UTC, storm ULLA, which had formed across the western North Atlantic two days before, was centred southwest of Ireland (Fig. 1). It relocated to the Irish See during the following 12 hours and then moved towards northern Scandinavia.

Fig. 1: Surface analysis on 14 February 2014, 12 UTC. Storm ULLA is located west of the British Isles. [Source: DWD]

In the waters southwest of the British Isles, particularly in the area of the Celtic Sea, it was very stormy in the afternoon of 14 February. This area lay to the right of the track of storm ULLA, where speed of movement and gradient wind (wind blowing around the centre of the low) add up. The wind turned from SSW to WSW in that region during the afternoon.

One of the ships, that were en route in the Celtic Sea at that time and reported data about weather and sea state, was the container ship „Liverpool Express“. It recorded winds from SSW at a speed of 50 kn (93 km/h), i.e. a wind force of 10 Bft (storm), and wave heights (wind sea as well as swell) of 8 m in position 49,7° N / 7,3° W at 12 UTC. The sky was cloudy and it rained slightly, while the visibility was 2 to 4 km.

At 15 and at 16 UTC, the buoy 62163, located in position 47,5° N / 8,4° W (at the southern border of the Celtic Sea), recorded wave heights of 13.4 m at a wind speed of 41/42 kn (76/78 km/h), i.e. a wind force of 9 Bft (strong gale). Figure 2 shows the development of se- lected parameters (sustained wind speed, peak gusts, wave heights, air pressure) at the buoy in the course of the 14th of February.

The wind was strongest between 10 and 17 UTC. The waves reached their peak heights when the cold front of storm ULLA passed at about 15 to 16 UTC.

Fig. 2: Data of buoy 62163 on 14 February 2014. Time data in UTC. Top: sustained wind and peak gust (each in knots). Middle: wave height (in metres). Bottom: air pressure (in hPa). [Source: DWD]

3 At midnight (15 February 2014, 00 UTC), the area with the highest significant wave heights (= mean height of the highest third of all waves in an observation period) of more than 14 m, relocated to the English Channel (Fig. 3).

Fig. 3: Wind (black arrows), swell (red arrows), significant wave height (coloured, in metres) and air pressure (lines, in hPa) in the area of north-eastern Atlantic / North Sea on 15 Febru- ary 2014, 00 UTC. The central pressure of the intense low ULLA, located across the Irish Sea, was about 960 hPa. [Source: DWD]

Wind and sea state in the area of the Celtic Sea in February

Climatological analyses of the ERA-40 reanalysis for the period of 1971-2000 show that, on the global scale, the number of days per year with wind speeds of more than 24 m/s (≥ Bft 10) as well as the number of days per year with significant wave heights of more than 9 m is highest across the North Atlantic (Sterl and Caires, 2005).

An analysis of observation data from ships, which was collected between 1960 and 2002, gives more detailed information on the average wind and sea state conditions in the area of the Celtic Sea in February: In February, the wind across the Celtic Sea blows mostly from southwest to west. Wind forces of 4 to 5 Bft occur most frequently, while 10 to 12 Bft are very rare. The mean wave height is about 2 m in February. In about 95 % of the cases the wave height is below 5 m. Therefore higher waves can be classified as a rare event.

4 Sources and further information

. Bundesamt für Seeschifffahrt und Hydrographie (BSH): Naturverhältnisse, Westeuropäi- sche Gewässer. Hamburg und Rostock, 2003. . Cable News Network (CNN): British cruise line: Passenger killed after ‘freak wave’ hits ship. (February 18, 2014) http://edition.cnn.com/2014/02/14/world/europe/uk-cruise-ship-death/ . Cruise and Maritime Voyages Ltd: Media Statement Friday 14 February 2014 (2200hrs). http://www.cruiseandmaritime.com/media-statement-friday-14-february-2014-2200hrs . Cruise and Maritime Voyages Ltd: Media Statement Saturday 15 February 2014 (1200hrs). http://www.cruiseandmaritime.com/media-statement-saturday-15-february-2014-1200hrs . Cruise and Maritime Voyages Ltd: Media Statement Sunday 16 February 2014 (1530hrs). http://www.cruiseandmaritime.com/media-statement-sunday-16-february-2014-1530hrs . Deutscher Wetterdienst (DWD): Data archive. . Deutscher Wetterdienst (DWD): Storm surge on the European Atlantic coast in early Feb- ruary 2014. . Deutscher Wetterdienst (DWD): Sturm und Regen in Westeuropa, Februar 2014. . Europäisches Segel-Informationssystem (ESYS): Fähre riss sich im Sturm in Calais los. http://www.esys.org/news/sos.html . Europäisches Segel-Informationssystem (ESYS): Svendborg Maersk verlor im Englischen Kanal 50 Container. http://www.esys.org/news/sos.html . Europäisches Segel-Informationssystem (ESYS): Tod am Ende der Kreuzfahrt. http://www.esys.org/news/sos.html . Marine Traffic http://www.marinetraffic.com/de/ . Marine Traffic: Marco Polo. http://www.marinetraffic.com/de/ais/details/ships/6417097/vessel:MARCO_POLO . Mobile Geographics LLC: Live marine information. http://www.sailwx.info/index.html . ms Marco Polo Cruises: Marco Polo cruise ship passenger death 2014 accident. http://www.marcopolocruises.net/ms-marco-polo-accident/ . Sterl, A.; Caires, S. (2005): Climatology, variability and extrema of ocean waves: The web- bases KNMI/ERA wave atlas. Int. J. Climatol. 25, 963-977. http://onlinelibrary.wiley.com/doi/10.1002/joc.1175/pdf . Wikipedia: Celtic Sea. http://en.wikipedia.org/wiki/Celtic_Sea