Hurricane activity in the Atlantic basin and making landfall in the US will be 65 percent above normal during 2007, predicts the Tropical Storm Risk consortium.

Five tropical storms, of which two will be hurricanes, are forecast to strike the US, while two tropical storms — one a hurricane — will visit the smaller Caribbean islands.

That is the long-range prediction of the Benfield co-sponsored Tropical Storm Risk (TSR) consortium, which has a good recent track record having correctly predicted the exceptional activity of the 2004 and 2005 hurricane seasons.

The consortium has categorised the 2007 hurricane season, which officially started last Friday, as being an "active to high" activity season.

According to TSR the probability of an above average hurricane season is 84 percent, with a 13 percent probability of a near-normal season and only a three percent chance of a below-normal season.

It has predicted 16 tropical storms in the Atlantic basin, of which nine will be hurricanes and four "intense" hurricanes.

Three main climate factors will be closely monitored over the next two to three months to determine with more accuracy how active the developing hurricane season will be. These factors have been outlined by professor Mark Saunders, lead scientist with TSR, as:

[bul] The speed of trade winds blowing westward across the tropical Atlantic and Caribbean Sea during August and September. The cyclonic vorticity and vertical wind shear over this main hurricane-producing tract of water can either help or hinder hurricane development depending on their strengths.

[bul] The temperature of sea waters between West Africa and the Caribbean. Higher sea temperatures provide the heat and moisture that powers the development of storms.

[bul] The presence of African dry air and Saharan dust over the hurricane development area. Dry air and dust in this region subdued hurricane activity in the early part of the 2006 season.

A fourth factor that gives specific indication of whether or not hurricanes will reach the US mainland is tropospheric wind anomalies between the heights of 925mb and 400mb over North America, the east Pacific and the North Atlantic. Anomalies in this section of the troposphere during July can influence the air circulation patterns that favour or hinder hurricanes reaching the US in the peak months of August and September.

While the hurricane season is predicted as being 65 percent more active than the norm, it is not likely to be as destructive as those of 2004 and 2005.

"A repeat of the devastation seen in 2004 and 2005 is unlikely. The more likely scenario is that 2007 will produce US landfalling activity close to or slightly above the 1995-2006 norm level," said professor Mark Saunders, who is also head of Weather and Climate Extremes for Benfield UCL Hazard Research Centre at University College London.

The TSR consortium brings together climate physicists, meteorologists and statisticians at University College London and the UK Met Office.

TSR forecasts are posted on the web site www.tropicalstormrisk.com