Cyclone Hergen

Cyclone Hergen

Hergen on 13 December 2011
Type European windstorm, Extratropical cyclone
Formed 11 December 2011[1]
Dissipated 19 December 2011[2]
Lowest pressure 945 mb (27.9 inHg)
Areas affected Newfoundland, United Kingdom, Ireland, Norway

Cyclone Hergen was an intense European windstorm that moved across Northern Europe during mid December 2011. It was first noted over the central North Atlantic Ocean by the Met Office. It then later reached peak intensity just northwest of Ireland and then crossed the north of Scotland hours later. It hung around the coast of Norway for the next week before being absorbed by another strong windstorm named Joachim.

Hergen was not the first storm to strike Western Europe during the last week as Cyclone Friedhelm brought widespread damage and very strong winds on 8 December. Hergen was followed by Joachim a few days later, then Oliver/Patrick (Cato/Dagmar) during the Christmas holiday. Cyclone Ulli then brought major damage and flooding to Northern Europe during the early part of January 2012.

Meteorological history

On 11 December 2011, the Met Office had noted a complex weather system over the central Atlantic, associated with several warm and cold fronts.[3] An amplified jet stream—a strong and fast-moving airstream aloft—advanced eastward, sparking rapid cyclogenesis along the fronts.[4] By the following day, a low-pressure centre had developed along an occlusion between two of the fronts. The low rapidly deepened as it approached the British Isles,[5] with a developing occluded rainband producing sustained winds of up to 60 mph (95 km/h).[6] It later deepened to a minimum barometric pressure of 945 mb (27.9 inHg), centred just northwest of Ireland.[7] A 67 feet (20 m) wave was recorded off the coast of Donegal at 1400 UTC on 13 December.[8][9][10] On 14 December, Hergen had moved slightly to the northeast while centred just off the coast of the Shetland Isles.[11] By this time, the system had lost its weather fronts.[12] The storm moved slowly offshore Norway for the next few days before being absorbed by the larger Cyclone Joachim on 19 December.

Preparations and warnings

On 10 December, a low pressure system formed over Labrador. This storm rapidly deepened as it moved towards the United Kingdom, which led to the Met Office issuing severe weather warnings.[13] At the time, the forecast storms were considered to be equivalent to a Category 4 hurricane on the Saffir-Simpson Hurricane Scale. The storm was only expected to strike parts of England and Wales.[14] Forecasters at multiple meteorological agencies in the United Kingdom said that snow could fall in southern England which would have been the first of the season.[15] They also said that winds could reach 100 mph (160 km/h), however, there was not much confidence with this prediction.[16]

Impact

The low brought strong winds and rain to Hampshire, flooding streets and felling trees. In some areas, the winds reached speeds of 70 mph (110 km/h), just below hurricane force. A 60 ft (18 m) tree crashed down onto a home in Winchester, causing heavy damage and almost killing a resident inside.[17] In Kent, the Port of Dover was shut from 10:30 p.m. to 5:30 p.m. GMT on 11–12 December.[18] The Scotland transport minister warned of snow and strong winds which could have led to widespread travel disruption.[19] Icy conditions prevailed in Scotland, Northern Ireland and Northern England early on 13 December.[20]

In Norway, a ferry was delayed by 17.5 hours by the large waves caused by the storm, leaving some injured.[21]

References

  1. ↑ "December 11, 2011 surface analysis". Institute of Meteorology. Free University of Berlin. Retrieved 12 December 2011.
  2. ↑ "December 19, 2011 surface analysis". Institute of Meteorology. Free University of Berlin. Retrieved 16 January 2012.
  3. ↑ Surface pressure forecast: Met Office view of 0000 UTC surface analysis (Report). Exeter, United Kingdom: Met Office. 12 December 2011. Archived from the original on 12 December 2011. Retrieved 13 December 2011.
  4. ↑ Severe Thunderstorm Watch #068 (Report). SkyWarn UK. 12 December 2011. Archived from the original on 12 December 2011. Retrieved 13 December 2011.
  5. ↑ Surface pressure forecast: Met Office view of 0000 UTC surface analysis (Report). Exeter, United Kingdom: Met Office. 13 December 2011. Archived from the original on 13 December 2011. Retrieved 13 December 2011.
  6. ↑ SkyWarn UK severe weather watch #069 (Report). London, United Kingdom: SkyWarn UK. 13 December 2011. Archived from the original on 13 December 2011. Retrieved 13 December 2011.
  7. ↑ "December 13, 2011 surface analysis". Met Office. Wetterzentrale. Retrieved 19 March 2012.
  8. ↑ "Record wave recorded off Ireland". Dublin, Ireland: Met Eireann. 13 December 2011. Archived from the original on 8 January 2012. Retrieved 13 December 2011.
  9. ↑ "Record Wave Off Ireland – More Information Breaks". Build.ie. 13 December 2011. Retrieved 14 December 2011.
  10. ↑ "Surfer Snapped Riding Monster Irish Waves". Sky News. 14 December 2011. Retrieved 14 December 2011.
  11. ↑ "December 14, 2011 surface analysis". Institute of Meteorology. Free University of Berlin. Retrieved 17 January 2012.
  12. ↑ "December 15, 2011 surface analysis". Institute of Meteorology. Free University of Berlin. Retrieved 19 March 2012.
  13. ↑ "Storm warnings issued as Britain braces itself for more severe weather". Metro. 12 December 2011. Retrieved 14 December 2011.
  14. ↑ "Storms And Gale-Force Winds To Lash Britain". Sky News. 11 December 2011. Retrieved 14 December 2011.
  15. ↑ "Snow to hit southern England as severe storms batter UK". Telegraph. 11 December 2011. Retrieved 29 January 2012.
  16. ↑ "UK Braced For More Storms After 165MPH Gales in Scotland". The Huffington Post. 11 December 2011. Retrieved 29 January 2012.
  17. ↑ Davies, Sian (13 December 2011). "Weather causes havoc across Hampshire". Daily Echo. Weybridge, United Kingdom: Newsquest. Retrieved 13 December 2011.
  18. ↑ "Kent braced for more winds this week as stormy weather returns". Kent Online. 12 December 2011. Retrieved 29 January 2012.
  19. ↑ "More storms expected to hit UK". Daily Post. 13 December 2011. Retrieved 19 March 2012.
  20. ↑ "Winds of 70mph Batter Parts of Britain". Sky News. 13 December 2011. Retrieved 19 March 2012.
  21. ↑ "New storm upset ferry travel". Views and News from Norway. 15 December 2011. Retrieved 20 March 2012.
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