Georgia Tech: Hurricane Size Related to Increased Threat of Tornadoes

An increase in the size and frequency of Gulf Coast hurricanes appears to correlate to an increased threat of tornadoes that typically occur once hurricanes move inland, according to researchers at the Georgia Institute of Technology.

"As the size of land-falling hurricanes from the Gulf of Mexico increases, we're seeing more tornadoes than we did in the past that can occur up to two days and several hundred miles inland from the landfall location," said James Belanger, doctoral student at Georgia Tech in the School of Earth and Atmospheric Sciences, in a statement announcing the findings.

Belanger, along with Judith Curry, professor and chairwoman of the school, and research scientist Carlos Hoyos said they created a model using records since 1995. Prior to that, technology did not exist to accurately quantify the risk of tornadoes forming from hurricanes. The team found that since 1995 there has been a 35% increase in the size of tropical cyclones in the Gulf when compared with a previous active period from 1948-1964, which has led to a doubling in the number of tornadoes produced per storm.

Running past hurricanes through the model, the team said it predicted 33 tornadoes from Hurricane Ike last year. There were 33 tornadoes from that storm. The model predicted 56 tornadoes from Hurricane Katrina in 2005. There were 58 tornadoes from that storm.

"The size of a tropical cyclone basically sets the domain over which tornadoes can form," said Belanger. "A larger storm that has more exposure over land has a higher propensity for producing tornadoes than a smaller one, on average."

According to a special report from A.M. Best Co. released in April, tornado activity in 2008 was among the worst on record. Of the 29 severe thunderstorm catastrophes in 2008, two events each resulted in insured losses of $1 billion or more and four events caused losses of $725 million or more. Tornadoes and weather events have caused nearly 57%, on average, of all insured catastrophe losses in the United States since 1953.

Belanger, Curry and Hoyos said they next plan to tackle how hurricane size, not just its intensity, affects damage potential to coastal residents.