2012 Atlantic hurricane season: eventful but not extraordinary

Hurricane Sandy left behind scenes of devastation along the US East Coast which people will remember for a long time to come. But the storm came at the end of a hurricane season that by most scientific measures was nothing out of the ordinary.

The Atlantic hurricane season officially ended on 30 November. Looking back, it may have been eventful but it wasn't anything unusual. Two significant storms made landfall in the United States:  Hurricane Isaac in Louisiana in August and Hurricane Sandy in New Jersey in late October. Indeed, Sandy broke numerous records as it hit the Northeast, exceeding storm surge records with tides reaching 10-14 feet (3-4 metres) at Battery Park and Sandy Hook.

Accumulated cyclone energy a better indicator

With the benefit of hindsight, we now know that most forecasters overestimated the expected occurrence of major hurricanes but underestimated the total number of named storms and hurricanes this year. 2012 marks the third year in a row where 19 named storms have formed, with four storms developing before 1 July. In numerical terms, this makes 2012 tied for the third most active year along with 2010, 2011 and 1995.  Only 1933 and 2005 had more tropical cyclones, with 20 and 28 respectively. Responsible for this high activity is a warm phase over the Atlantic we've been experiencing since 1995, a natural variation in the climate system that normally persists for 25 to 40 years.

However, a high storm count is not a very good indicator for the activity of an entire hurricane season. A better measure is "accumulated cyclone energy (ACE)," the sum of the square of the maximum sustained wind speed every six hours. Strong, long-lasting hurricanes have high ACE values while weak, short-lived tropical storms have low ACE values. The ACE of a season is the sum of the ACE for each storm. For example, Hurricane Ivan in 2004 was a long-lived, powerful hurricane and its ACE value of 70 exceeded the entire ACE of the 2009 season at 51.

Serving clients with our hurricane risk assessment expertise

2012 has an ACE value of 123 for the season, which is only slightly higher than the long-term seasonal average of 103. By comparison, 1950 had only 13 named storms but 8 major hurricanes, giving it an ACE value of 243. Moreover, many of storms that did occur this year stayed well away from any landmasses. So while from a pure storm count perspective 2012 seems like an active hurricane season, when ACE and geography are considered 2012 is one for the record books only because of Sandy.

For the insurance industry, estimating the expected loss and damage from hurricanes is a complex task, particularly as sea level rise could further increase the risk of storm surge. Swiss Re is proud to have its own in-house risk assessment model and is confident that this expertise allows us to better serve our clients and outperform our competitors.

Institution Date Named storms
Hurricanes Named hurricanes
Colorado State
 4/2012  10  4  2
Tropical Storm Risk
 5/2012  13  6  3
Accuweather  5/2012  12  5  2
National Hurricane Center
 5/2012  9-15  4-8  1-3
Colorado State  6/2012
 13  5  2
Tropical Storm Risk  8/2012
 14  6  3
National Hurricane Center  8/2012  12-17  5-8  2-3
Average    12  6  3
1995-2010 average
   15  8  4
Actual  12/2012  19  10  1
Final numbers and forecasts of named storms, hurricanes and major hurricanes for 2012  

Published 19 December 2012

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2012 Atlantic hurricane season

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