In terms of number of storms reaching at least hurricane intensity, 2013 is the quietest hurricane season since 1982 according to RMS senior director Brian Owens. 2013 is also the eighth year in a row without a major hurricane making landfall in the US. Hurricane Wilma in 2005 was the last major hurricane to touch ground on the US coast, the longest stretch without such a storm since the 1860s.
Owens said: “it was a particularly quiet year. The total number of tropical storms that occurred was slightly above average, but the number of hurricanes and major hurricanes was clearly well below average.”
He continued: “that’s not to say that the past eight seasons have not been busy. There has been plenty of hurricane activity going on in the Atlantic hurricane basin– we’ve had several above-average seasons—but there have been relatively few hurricanes, and no major hurricanes, making landfall in the US. Of course you don’t need a major hurricane to experience a large storm surge, as we saw with Superstorm Sandy.”
While the number of tropical storms was slightly above average at 13—normally expectations hover around 10 or 11 —those that formed for the most part did not develop into hurricanes. As a result the frequency of hurricanes and major hurricanes was much lower than in an average season. Only two hurricanes managed to form during the normally busiest part of the season between August and October; neither was a major storm.
The phase of El Nino Southern Oscillation (ENSO) is one of the most important factors to consider. It was neutral for the 2013 season, which should have been reasonably favourable for hurricane development. Owens explained: “the other main factor was that sea surface temperatures over a large part of the Atlantic were cooler than normal. That took away the principal source of energy that helps to drive the genesis and the development of hurricanes.”
Dry wind from the Sahara Desert inhibited tropical waves coming off of the coast of Africa and reduced atmospheric instability also put a damper on storm formation. Owens said: “it was a combination of factors, really, that helped contribute to the overall lower level of major hurricanes.”
While it’s far too soon to say what 2014’s hurricane season might look like, Owens indicated that the phase of ENSO and Atlantic and Gulf of Mexico sea-surface temperatures would be closely followed by RMS as the season approaches. He said: “during the season we would be watching for things like wind shear and other factors affecting tropical wave development such as Saharan dry air.”
Overall, Owens said: “the 2013 season fits in very much with our research, which finds that during these periods when we’re getting busier hurricane seasons it’s often associated with storms forming further to the east out in the Atlantic. Busy seasons are not necessarily transferring to landfall in the US, and we reflect that research in our model.”
RMS, hurricanes, modelling