J3.3
Hurricane Tornadoes 2004
Eugene W. McCaul Jr., USRA, Huntsville, AL
The year 2004 will be remembered not only for its large number of significant and damaging landfalling tropical cyclones, but also for the number and destructiveness of the tornadoes they spawned. According to preliminary counts, the six tornadic landfalling TCs spawned some 312 tornadoes, the most of any year since reliable records have become available. The TC tornadoes were the single biggest reason why both August and September posted record large tornado counts in 2004. To help put the 2004 season in perspective, recall that the number of tornadoes documented in the largest extant TC tornado climatology, which spanned a 39-year period from 1948-1986, was only 626 (McCaul 1991). The count for 2004 alone is almost half that amount! Thus, it appears that the 2004 season yielded some 15 YEARS worth of TC tornadoes, even accounting for the tendency for numbers to be larger in recent years owing to improved detection and reporting.
Of the six landfalling TCs that spawned tornadoes, two produced major outbreaks that rival the reigning champion, Hurricane Beulah of 1967. Frances spawned some 108 tornadoes from 4-8 September, only to be followed by Ivan, with another 108 tornadoes during 15-17 September. Ivan produced at least 4 killer tornadoes, the first TC to accomplish this feat since 1891, according to severe weather historian Tom Grazulis (Grazulis 1993). As of the end of September 2004, landfalling TCs had accounted for six of the 14 killer tornadoes in the United States, and 11 of the 28 deaths. More complete statistics will be presented at the conference in San Diego.
One of the biggest ironies of the 2004 season was the fact that all the TC tornadoes occurred east of a line extending from near Pensacola, Florida, up through the Appalachian Mountains. This was the result of a persistent flow pattern that featured a recurrent long-wave trough over or west of the Appalachians, with the western tip of the Bermuda High lying just east of the Georgia coast. As a consequence, many Atlantic coast states experienced the brunt of a number of major tropical cyclones, and saw either their biggest annual tornado totals or biggest tornado outbreaks of record. States like Virginia and South Carolina now sport larger peak annual tornado totals records than states farther west like Alabama and Mississippi. The TCs of 2004 have truly rewritten the tornado record books!
Although the favored geographical region for TC tornadoes in 2004 was unusually far east, the characteristics of the TCs themselves were well in line with what previous research has shown to be predictive of TC tornado productivity (see, e.g., McCaul 1991). The two biggest tornado producers, Frances and Ivan, were both quite large, and had peak intensity ratings of category 4 and 5 respectively, before interacting with the North American continent. Furthermore these TCs moved at moderate forward speeds, consistent with earlier climatologies which showed that TCs that move either too slowly or too fast tend to have diminished tornado potential. The TC tornado outbreaks were also well-behaved in the sense that nearly all the tornadoes occurred in the right-front or northeast quadrants of the TCs. Furthermore, the weak baroclinic boundaries identified in a recently published study of a 1994 TC tornado outbreak (McCaul {\etal} 2004) were also evident in the major TC tornado events of 2004. The tornadic potentials of Frances, Ivan and Jeanne were duly noted by the Storm Prediction Center, which for the first time issued a number of Moderate Risk outlooks for expected TC tornado activity.
Recorded presentationJoint Session 3, Living in the Coastal Zone (Joint between the IMPACT: 2004 Weather Symposium and the Third AMS Users Conference: Uses of and Needs for Weather and Climate Services in Managing Water Resources, Energy, and Ocean Transportation)
Tuesday, 11 January 2005, 1:30 PM-3:00 PM
Previous paper