Florida's tornadoes and El Ni�o

Friday's devastating tornadoes in Central Florida, where 20 people lost their lives, marked the second most deadly tornado outbreak in Florida history. Only the February 22-23, 1998 tornado outbreak in Kissimmee, which killed 42 and injured 260, was worse. Two of Friday's tornadoes were rated as EF-3 (Category 3 on the new Enhanced Fujita Scale), with winds near 160 mph. The Enhanced Fujita Scale became the official scale for rating tornadoes as of February 1, 2007, and Friday's tornadoes were the first to be ranked with the new damage scale. The new scale replaces the old Fujita Scale, which required winds of a tornado to be much higher in order to get an F3 or higher rating. Modern engineering studies have determined that devastating damage can occur at much lower wind speeds, and that the Fujita Scale did a poor job of correlating between damage and wind speed. For example, tornadoes capable of causing incredible damage (EF 5 rating) are now known to occur at wind speeds of 200 mph and higher. On the old F-Scale, an F-5 rating started at 261 mph. See the Tornado FAQ for a full comparison of the old Fujita Scale with the new Enhanced Fujita Scale.

Strong and violent tornadoes are rare in Florida, but when they do occur, it tends to be during winter when a moderate or strong El Ni�o event is occurring. More than 60% of Florida's killer tornadoes occur between midnight and noon, which was also the case with Friday's outbreak. This was the second major Florida tornado outbreak this winter. Earlier this winter, a series of three tornadoes, including two rated at F2, hit near Daytona Beach on Christmas Day, injuring 16 people. During El Ni�o winters, the jet stream winds tend to be stronger over Florida, a key ingredient needed for tornado activity (Figure 1).


Figure 1. Incidence of strong (F2 and higher) tornadoes over Florida between 1950 and 1998. Note the highest numbers of strong tornadoes occurred during the major El Ni�o years of 1983 and 1998. Image credit: NOAA.

Jeff Masters