When the wind blows

Calm in the Atlantic but Europe takes a buffeting

Wind Blows

Despite predictions of a stormy Atlantic hurricane season, 2013 was an extremely benign year - the least active in the last 30 years in fact.

Just 13 named storms formed during the year and only two – Humberto and Ingrid – reached hurricane strength. None reached the status of a major hurricane (category 3 or more). That compares to an average of 11 to 12 named storms in the Atlantic Basin during a season, with seven becoming hurricanes, and two to three reaching major hurricane status, between 1950 and 2012, according to risk modeller RMS.

The real question for the insurance industry raised by this is whether it could lead to risk modellers altering their hurricane risk assessments. The last major reassessment of hurricane risk came after the 2004 and 2005 Atlantic wind seasons, which were particularly active. Then, modellers revised their assessments upward, anticipating a greater number of hurricanes each season than previously.

In 2004 the hurricane season came late, but when it arrived it was ferocious, with more than half of the season’s 16 tropical cyclones brushing or striking the US. Hurricane Charley that year was the second-costliest hurricane in US history at the time, leaving a $14 billion trail of damage in its wake. The following year, 2005, was the most active Atlantic hurricane season in recorded history, causing around $159.2 billion in damage and an estimated 3,913 deaths. Subsequent Atlantic hurricane seasons have been quieter, with this latest one producing the fewest hurricanes since 1982.

Risk modelers look at a range of factors including long-term average numbers of hurricanes, the impact of El Nino, sea surface temperatures, and global warming to assess hurricane risks.

According to Jeff Waters, senior analyst, business solutions, at RMS, writing on the company’s blog, “…large-scale atmospheric signals, such as the absence of El-Niño conditions and warmer-than-average sea-surface temperatures across most of the tropical Atlantic, indicated an average to above average season.”

But, he adds, there are other factors that could have suppressed hurricane activity, including: drier-than-normal air settling in the eastern Atlantic that made it difficult for tropical waves coming off the West African coast to develop; reduced atmospheric instability during the season’s peak months (normally a driver of hurricane formation); and cool sea surface temperatures across the Atlantic that may have had a dampened the formation of hurricanes.

Another reason for this period of relative calm could be a slowdown in global warming since 1998. The Intergovernmental Panel on Climate Change reported in 2007 that the short-term global temperature rise would most likely be 1-3C (1.8-5.4F). But new analysis, arrived at by including temperatures from just the last decade, has led to a revision of this prediction to a projected range of 0.9-2.0C. Dr Alexander Otto, who is researching climate decisions at the Environmental Change Institute at the University of Oxford, told the BBC recently, “The hottest of the models in the medium-term, they are actually looking less likely or inconsistent with the data from the last decade alone. The most extreme projections are looking less likely than before.”

Whatever the reasons for the hurricane hiatus, confidence in weather modeling, and especially in short-term predictions, will have been eroded by the unexpectedness of this season and the quiet seasons preceding it.

In Europe, by contrast, the wind season got off to a stormy start when extratropical cyclone Xaver came ashore in Scotland on December 5, pummeling the country with wind speeds comparable to a category 1 hurricane, before moving across the North Sea to the Netherlands, Denmark and Germany. According to catastrophe modelling firm AIR Worldwide, insured wind losses from Xaver could be between 700m euros and 1.4 billion euros, with the majority coming from Denmark, Germany, and the UK.

Given the failure of short-term predictions about the Atlantic hurricane season, few are taking any guesses at how the European wind season will pan out.

It is even harder to predict a European wind season than the Atlantic one, because of the short time-span of phenomena that moderates the rate of arrival of winter storms in Europe – only one or two weeks, compared with months and years for hurricane formation in the US, according to Dr Renato Vitolo, Willis Research Fellow at the University of Exeter, who specializes in the predictability of extreme weather events.

In an interview with Lloyds.com, he said: “The linear autocorrelation in the signal decays quickly and is no longer significant after three weeks. I reckon that is the current limit of any ‘seasonal’ or ‘extended range’ forecast.”

Research produced by the University of Cologne a few years ago suggested there was a likelihood of less storms in the future but more intense ones across the North and Baltic seas on a similar path to windstorm Kyril. Kyril formed over Newfoundland on 15 January 2007 and moved across the Atlantic Ocean before hitting Ireland and the UK and then moving across the North Sea to make landfall along the Dutch and German coastlines, before moving toward Poland and the Baltic Sea and finally northern Russia.

Xaver, which took a similar route, could be a sign that further strong windstorms might follow that same trajectory, with the British Isles and northern Europe in their path.


BBC - Climate change means extreme rates of warming 'not as likely'

Image by Meriel Waissman

Posted: Monday, December 23rd, 2013