SECTION 4: RISK ASSESSMENT
4.5.11 TORNADO HAZARD BACKGROUND
According to the Glossary of Meteorology (AMS 2020), a tornado is "a violently rotating column of air extending vertically from the surface to the base of a cumuliform cloud, often with near-surface circulating debris/dust when over land or spray when over water. Although its presence is not required, a funnel cloud is often visible and may partly or fully extend from the cloud base to the ground." Tornadoes can appear from any direction. Most move from southwest to northeast, or west to east. Some tornadoes have changed direction amid path, or even backtracked. Tornadoes are commonly produced by land falling tropical cyclones. Those making landfall along the Gulf coast traditionally produce more tornadoes than those making landfall along the Atlantic coast. Tornadoes that form within hurricanes are more common in the right front quadrant with respect to the forward direction but can occur in other areas as well. According to the NOAA, more than half of the landfalling hurricanes will spawn at least one tornado. Tornadoes are more likely to be spawned within 24 hours of landfall and are usually within 30 miles of the tropical cyclone’s center. Tornadoes have the potential to produce winds in excess of 200 mph (EF5 on the Enhanced Fujita Scale) and can be very expansive – some in the Great Plains have exceeded two miles in width. Tornadoes associated with tropical cyclones, however, tend to be of lower intensity (EF0 to EF2) and much smaller in size than ones that form in the Great Plains.
Source: NOAA National Weather Service
Warning Time: 4 – Less than 6 hours
Duration: 1 – Less than 6 hours
According to the NOAA Storm Prediction Center (SPC), the United States experiences an average of
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 215
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