Variability in tornado frequency associated with U.S. landfalling tropical cyclones

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

James Belanger, lead-author

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• Develops a statistical model for tornado frequency from Gulf of Mexico landfalling tropical cyclones (TCs) using TC size, intensity, recurvature, and mid-level specific humidity data
• Assembles new datasets for tornado frequency and for TC size at landfall as measured by the radius of outer closed isobar and distance of tornado from the TC cente
• Uses the model—owing to systematic undercounting of tornadoes—to reconstruct the TC tornado climatology back to 1948, and further back to 1920 using a modified model that does not include mid-level specific humidity
• Finds the active period since 1995 has seen a statistically significant increase (95% level) in median TC tornadoes and in the frequency of large TC tornado outbreaks, relative to the previous active period for Gulf TC landfalls of 1948–1964
• Links these changes to an increase in the median size and frequency of large Gulf landfalling TCs