Connections between climate oscillations and tornado outbreaks in U.S. landfalling hurricanes

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Tuesday, 19 January 2010
Virginia G. Silvis, University of Oklahoma, Norman, OK

Every year the coastal United States faces the threat of tornadoes from hurricanes, whether or not landfall occurs. While most hurricanes often produce a few tornadoes upon coastal interaction, there have been several notable exceptions: Hurricane Beulah in 1967 produced 113 tornadoes, Hurricanes Frances and Ivan in 2004, 106 and 127 tornadoes respectively, and Hurricane Rita in 2005 generated 92 tornadoes. Most of these tornadoes were relatively weak, measuring F0-F1 strength, but both Frances and Ivan produced singular F3s. Tropical Storm Beryl in 1994 produced 3 F3s, and it is suspected that Hurricane Carla in 1961 produced a F4 tornado that hit Galveston, TX as the storm made landfall. About 10% of fatalities that occur as a result of hurricanes are due to these tornadoes. Because many of these tornadoes occur in the outer rain bands of hurricanes, those at highest risk from injury or death from these storms often are unaware of the risk they face.

In an attempt to mitigate hurricane-induced tornado risk, a statistical comparison is proposed of tornado outbreaks in landfalling hurricanes along the eastern Atlantic seaboard and Gulf Coast, the ENSO phase, and the Madden-Julian Oscillation in an effort to better predict outbreaks of these tornadoes. The hurricanes that occurred between 1960 and 2007 were sorted into tornado outbreak categories that distinguish between non-outbreaks and outbreaks and then multivariate statistical tests were used to compare that data to SSTs in the Pacific Ocean during the same time period. A relationship was found to exist between the above-mentioned climatic oscillations and outbreaks of tornadoes in landfalling/coastal-interacting hurricanes. It is anticipated that this connection can be used in a predictive capacity to provide improved forecasts of hurricane-related tornadoes prior to landfall, to educate the public, and to reduce the number of hurricane fatalities and destruction of property.