850 The Rising Frequency of Hurricane-Tornadoes: Possible Causes and Consequences

Wednesday, 26 January 2011
Washington State Convention Center
Virginia G. Silvis, Univ. of Oklahoma, Norman, OK

Investigating the cause of tornado outbreaks in land-falling and land-affecting hurricanes is a developing area of research in the field of meteorology; however, many of the people exposed to the greatest threat from these outbreaks are usually unaware of the danger. Since approximately 1995, when the Atlantic Multidecadel Oscillation (AMO) switched from a cold phase to a warm phase, the risk of tornado outbreaks upon hurricane landfall has increased as the accumulated cyclone energy (ACE) has increased. In recent years, hurricanes Frances and Ivan in 2004 produced 106 and 127 tornadoes respectively, and Hurricane Rita in 2005 generated 92 tornadoes. These numbers are a marked increase from the number of tornadoes produced during hurricane landfalls during the last cold AMO phase in the 1970s and 1980s. Most of these tornadoes were relatively weak, at F0-F1 strength, but both Frances and Ivan each produced singular F3s. This increased tornado hazard has often had deadly consequences with roughly 10% of hurricane fatalities occurring as a result of tornadoes.

With the increased risk of tornado outbreaks, it becomes more important to educate the public and the emergency responders in areas affected by hurricanes about dealing with these specific outbreaks. Although any area affected by a hurricane is at risk for hurricane-generated tornadoes, certain regions, such as the Gulf coast, are under a higher risk due to the coastline orientation and other characteristics of the hurricanes that affect the area. If the meteorological community can more effectively communicate the risk to emergency managers and the public, particularly those who choose not to evacuate, hopefully the death and injury toll due to hurricane-generated tornadoes can be dramatically reduced.

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