Leading risk modelling company AIR Worldwide Corporation yesterday suggested that a likely higher incidence of Atlantic storm activity does not necessarily equate to a risk of more hurricanes making landfall in the US.

Research by a team of AIR scientists has determined that where a hurricane makes landfall is heavily influenced by its starting point, or 'genesis location'. And such a technique could lead to more accurate estimations of where a storm is headed and also of potential insured losses.

The Bermuda reinsurance industry paid out billions in claims following a series of major hurricanes hitting the US in 2004 and 2005, but expectations of further damaging years in 2006 and 2007 proved unfounded — even though Atlantic storm activity was high, as many scientists had predicted.

"By only focussing on the 2004 and 2005 seasons, it is easy to forget that every hurricane season is unique and actual landfall activity is a function of complex interactions between a range of environmental factors such as genesis location, sea surface temperatures and the depth of warm ocean waters, wind shear and atmospheric steering," said Dr. Peter Dailey, director of research in atmospheric science at AIR Worldwide.

"A higher number of tropical storms in the Atlantic basin does not translate to an equivalent increase in hurricanes or landfalling hurricanes."

The pattern of hurricane genesis locations changes from year to year and by comparing the pattern for a particular season to long-term climatological patterns, it is possible to understand why in some years the proportion of storms making landfall is high, while in other years it is low.

AIR's research can be used to analyse the landfall probabilities of the two strongest storms of the 2007 season — category-five hurricanes Dean and Felix — based on their genesis locations. Dean and Felix, which were the only storms this year to achieve greater than category-one status, both took southerly tracks across the Caribbean and eventually made landfall along the coasts of Mexico and Central America.

"Contrary to popular belief, the US did not 'dodge a bullet' with respect to Hurricanes Dean and Felix," Dr. Dailey said. "Based on where these storms formed and how they would track under typical steering conditions, our research shows that Hurricane Dean had a low chance of making landfall as a hurricane and Felix was much more likely to strike the Mexico or Central America coastline than the US."

Sea surface temperatures in the Atlantic basin have been warmer than average every year since 1995. However, the percentage of Atlantic basin storms that make US landfall as hurricanes has been below the long-term average of 14 percent in nine of those 13 seasons, according to AIR.

In 2007, only one of 15 named storms made US landfall as a hurricane, or less than seven percent. More significantly, total wind energy in 2007 was 33 percent below average despite two category-five storms.

"The seasonal forecasters correctly projected that a higher-than average number of tropical storms would form in the basin in 2007," continued Dr. Dailey. "But it's much more difficult to predict not only how many of these storms will become hurricanes, but more importantly how many will make landfall as hurricanes.

"Like many past seasons, the 2007 season showed that an elevated number of tropical storms does not always translate to more hurricanes or more landfalling hurricanes. In 2007, sea surface temperatures were not as warm as some scientists expected and significant wind shear suppression by La Niña did not materialise as they had anticipated.

"Clearly there's a danger in assuming that one or two single seasons are indicative of a paradigm shift in hurricane risk. While 2004 and 2005 were both very active seasons, they were not good predictors of activity in 2006 and 2007."