RMS tells GR that storm displayed ‘unprecedented characteristics’

At first sight, it seemed like Bertha was just like all the rest. She arrived on the scene in the first week of July, a full four weeks into the Atlantic hurricane season.

However, there are several factors which were exceptional about the hurricane, according to catastrophe modellers at RMS – factors which modellers and reinsurers alike might consider noteworthy as an indication of future events.

Firstly, no other hurricane has formed so far east so early in the year. In fact, it formed as a storm close to the Cape Verde Islands off the west coast of Africa.

“This is unprecedented for this time of year,” said Neena Saith, catastrophe response manager at RMS, who added that the Cape Verde season does not typically kick off until August, when sea surface temperatures are warm enough to support tropical cyclone activity.

The concern for reinsurers is that the Cape Verde storm zone is often a breeding ground for storms that become a problem on the western side of the Atlantic.

“Many storms that have formed in this region during August and September have gone onto make landfall in the Caribbean or US,” Saith added.

“While historical data show that no storms have developed as far east as this during July, in 1999 tropical storm Alex developed about 200 miles west southwest of Bertha's location at the end of July, and a previous Hurricane Bertha in 1996 formed about 850 miles west southwest of the 2008 Bertha's location on July 5 and tracked across the Atlantic reaching category 3 status, making landfall in South Carolina as a category 3 storm.”

While Bertha looks unlikely to reach land and has since been downgraded to a Category 2 storm, catastrophe modellers are yet to declare whether she is a sign of things to come in 2008. However, they confirm that sea surface temperatures off the coast of Africa have been unusually high between late June and the present, reaching as much as 2ºC above average. Sea surface temperatures have a significant correlation with frequency of hurricanes.