Albany Tornado, Tuesday 03 May 2011
Tornadoes in New Zealand are generally quite different from the supercell tornadoes which occur, for example, in the mid-west of the United States primarily in the warm part of the year. In New Zealand, tornado occurrence is more often than not related to convection along strong cold fronts – a “cold season” phenomenon (Hanstrum et al, 2002). This does not, however, entirely confine tornadoes of this type to the winter months. Some notable recent instances include the Waitara tornado of 15 August 2004, the Greymouth tornado of 10 March 2005, the New Plymouth tornadoes of 3-4 July 2007 and the Cambridge tornado of 17 October 2008. Supercell tornadoes are rare in New Zealand. However, the Methven tornado of 14 December 2009 was an example of such a warm season supercell event, with similarities to larger convective events that typically occur in highly sheared environments. The Albany tornado of Tuesday 03 May 2011 had some of the characteristics of a supercell tornado. However, it appears not to have been associated with a thunderstorm, severe or otherwise. Radar imagery reveals the presence of a mesocyclone, indicating a strong low-level rotating updraft, but which was poorly defined for much of its lifetime. Additionally, there appears to be no strong evidence of a rear-flank downdraft.