BioEd Online

Those living on the hurricane-buffeted east coast of the United States, or those who sell them insurance, will probably take notice of a model that predicts the annual damage done by such storms.

The model, based on wind patterns over the land and sea in July, can predict whether damages will be greater or less than average in the storm season from August to October.

Previous models have been able to forecast the number of hurricanes forming at sea, based on variables such as ocean temperature, or fluctuations in air pressure over the North Atlantic Ocean. But even with a completely accurate forecast of hurricane formation it is difficult to say how many will make it to land.

Mark Saunders and Adam Lea of University College London's Benfield Hazard Research Centre in Dorking, UK, have extended previous work to form robust predictions of the financial damage in a hurricane season. Using their model on past years, they could say whether a year would see damages that were above or below average in 74% of cases, they report in Nature¹.

"This offers the potential to significantly reduce the financial risk and uncertainty associated with the hurricane season," says Saunders.

Winds of change

The team garnered data about winds in the troposphere, which extends about 10 kilometres up from the surface of the Earth, from 1950 to 2003. From these they identified persistent wind systems, dubbed 'steering winds', in six key regions. Together, these winds seem to determine whether the coming season will be a bad one for US residents. Near Bermuda, for example, unusually high pressures in July can cause onshore winds that consistently blow towards the US coast for the remainder of the summer.

Hurricane systems tend to form in the tropical North Atlantic before drifting westwards, Saunders explains. If they encounter a steering wind pointing away from the coast they will swerve harmlessly back out to the ocean. But if the steering winds are pointing towards land, the storms are funnelled on to the shore.

The researchers are not sure why the steering winds remain consistent for the entire summer. "There's lots of day-to-day variation," says Saunders. "But overall the winds do seem to persist for around three months."

Premium savings

"This will be really important for insurance companies," says David Simmons, a risk consultant for Benfield, a London-based reinsurance company. When faced with the possibility of a catastrophic event, insurers need to decide whether they will buy more coverage or not. The authors claim that over time, insurers could save 30% on their returns and premiums using this model.

In fact, says Saunders, they had a chance to do so last year, when a devastating sequence of four hurricanes cost insurance firms billions. The researchers used an early version of their model to forecast a worse-than-average season. "If they had used our forecast they could have saved themselves money," says Saunders.