Doppler Radar and Lightning Network Observations of a Severe Outbreak of Tropical Cyclone Tornadoes

Abstract

Data from a single Weather Surveillance Radar-1988 Doppler (WSR-88D) and the National Lightning Detection Network are used to examine the characteristics of the convective storms that produced a severe tornado outbreak, including three tornadoes that reached F3 intensity, within Tropical Storm Beryl's remnants on 16 August 1994. Comparison of the radar data with reports of tornadoes suggests that only 13 cells produced the 29 tornadoes that were documented in Georgia and the Carolinas on that date. Six of these cells spawned multiple tornadoes, and the radar data confirm the presence of miniature supercells. One of the cells was identifiable on radar for 11 h, spawning tornadoes over a time period spanning approximately 6.5 h. Several other tornadic cells also exhibited great longevity, with cell lifetimes longer than ever previously documented in a landfalling tropical cyclone (TC) tornado event. This event is easily the most intense TC tornado outbreak yet documented with WSR-88Ds.Time-height analyses of the three strongest tornadic supercells are presented in order to document storm kinematic structure and to show how these storms appear at different ranges from a WSR-88D. In addition, cloud-to-ground (CG) lightning data are examined in Beryl's remnants. Although the tornadic cells were responsible for most of Beryl's CG lightning, their flash rates were only weak to moderate, and in all the tornadic storms the lightning flashes were almost entirely negative in polarity. A few of the single-tornado storms produced no detectable CG lightning at all. There is evidence that CG lightning rates decreased during the tornadoes, compared to 30-min periods before the tornadoes. A number of the storms spawned tornadoes just after producing their final CG lightning flashes. Contrary to the findings for flash rates, both peak currents and positive flash percentages were larger in Beryl's nontornadic storms than in the tornadic ones.

Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands

“…If these flows fail to create inland fields of boulders, a tornado moves the stones, as did a waterspout in New Zealand (de Lange et al 2006). The boulders move southward because the front-right quadrants of hurricanes commonly contain tornadoes (Novlan and Gray 1974) that move in the same direction as the vortex winds (McCaul 1987;McCaul et al 2004). As the hurricane moves west of Anegada the vortex winds of its trailing quadrant drive a storm surge ashore from the south.…”

Tropical cyclone-tornado casualties

“…TCTs are also potentially hazardous at inland locations in front of a TCs projected trajectory where residents may not yet be expecting severe weather (Spratt et al 1997;McCaul et al 2004). Furthermore, Brommer and Senkbeil (2010) reported that TCTs are less of an influence, compared to storm intensity and geometric size, storm surge, and rainfall, on evacuation decisions.…”

“…Even though the risk of TCTs might not be a significant factor in evacuation decisions, they do have the potential to significantly impact nonevacuees along with evacuees en route and at their temporary destination. McCaul et al (2004), for instance, noted that residents of coastal Texas evacuated inland to locations that subsequently experienced numerous strong TCTs associated with Hurricane Allen (1980).…”

“…Research has also been devoted to the formation, detection, and forecasting of TCTs (Edwards 1998;Curtis 2004;McCaul et al 2004;Schneider and Sharp 2007;Edwards 2008). When documenting overall fatalities associated with Atlantic TCs from 1970 to 1999, Rappaport (2000) classified TCrelated fatalities by cause of death and found that 4% (approximately 24 fatalities) of all TC-related fatalities were attributed to TCTs.…”

A Bayesian modelling framework for tornado occurrences in North America

“…There are significant differences in the relative magnitudes of moisture, instability, shear and lift in conditions preceding TC tornadoes 29 . The smaller-scale boundaries associated with TC tornadoes are distinctly different from those of large-scale extratropical cyclones in spring and late autumn 30 . TC tornadoes are also associated with stronger lower troposheric vertical shear compared with those on the Great Plains 29 , which explains the stronger (weaker) and more (less) identifiable influence of SHEAR (VWSH), particularly for F2-F5 tornadoes.…”