Environmental Ingredients for Supercells and Tornadoes within Hurricane Ivan

Abstract

Hurricane Ivan (2004) was a prolific producer of tornadoes as it made landfall on the U.S. Gulf Coast. Prior researchers have revealed that the tornadic cells within tropical cyclone (TC) rainbands are often supercellular in character. The present study investigates the utility of several common midlatitude, continental supercell and tornado diagnostic tools when applied to Hurricane Ivan's tornado episode.The environment within Hurricane Ivan was favorable for storm rotation. While well offshore, the bands of Hurricane Ivan possessed embedded cells with mesocyclones of moderate intensity. A dual-Doppler analysis reveals that the updrafts of these cells were highly helical in the lower troposphere, suggesting significant ingestion of streamwise environmental vorticity. These coherent cells were long lived and could be tracked for multiple hours. As the supercells over the Gulf of Mexico approached the coast during Ivan's landfall, rapid increases in midlevel vorticity and vertically integrated liquid (VIL) occurred. Based on compiled severe weather reports, these increases in storm intensity appear often to have immediately preceded tornadogenesis.The local environment for supercells in Ivan's interior is evaluated through the use of 62 soundings from the operational land-based network and from research flights. There were substantial differences in the thermodynamic profiles and wind profiles at differing ranges from Ivan's center, from quadrant to quadrant of Ivan's circulation, and between land and sea. The most optimal environment for supercells and tornadoes occurred in the most interior section of Ivan's right-front quadrant, with conditions being even more favorable over land than over the sea. For contrast, comparable values are presented for Hurricane Jeanne (2004), which was similar to Ivan in several respects, but was not a prolific tornado producer at landfall. Although both storms provided environments with comparable shallow-and deep-layer vertical wind shear, the Ivan environment had notably more CAPE, likely due to a prominent dry air intrusion. This increase in CAPE was reflected in substantial increases in common operational forecasting composite indices. The results suggest that the conventionally assessed ingredients for midlatitude continental supercells and tornadoes can be readily applied to discriminate among TC tornado episodes.

Distribution of Helicity, CAPE, and Shear in Tropical Cyclones

“…The empirical parameters used in this study support the possible existence of supercells in tropical cyclones, especially in the downshear right quadrant outside of the 100-km radius. Supercells have been observed in tropical cyclones after landfall (e.g., McCaul et al 2004) and near land (Baker et al 2009). Radar data are needed to confirm whether such cells occur in tropical cyclones over open ocean.…”

Numerical Simulation of Cyclone Sidr Using a Cloud-Resolving Model: Characteristics and Formation Process of an Outer Rainband

“…A K T E R A N D T S U B O K I band and indicates a supportive environment for convection with strong updraft (McCaul 1991;McCaul and Weisman 2001;Baker et al 2009). In addition, the hodographs (Fig.…”

Pre-landfall evacuee perception of the meteorological hazards associated with Hurricane Gustav

“…5e. Tornado occurrences are common with land-falling hurricanes (e.g., Baker et al 2009) as a result of the unique atmospheric dynamics present within the rainbands of the storm. In a majority of instances, tornadogenesis is most frequent in the right-front quadrant of the hurricane (McCaul 1991), but can also occur in regions where local-scale atmospheric boundaries promote the rapid formation of tornadoes (Edwards and Pietrycha 2006).…”