Update: The MetService has blog has been updated to redefine the weather event as a ‘mircoburst’ rather than a tornado.
A tornado struck Auckland amidst heavy weather at 12.15pm today.
Three people are reported dead and a further seven in hospital following extreme winds and weather damage centred around the suburb of Hobsonville.
Emergency services are currently attending sites of infrastructure damage with military and Urban Search and Rescue personnel assisting.
Auckland Civil Defence is providing current information, advice and updates on the situation.
Concerns remain that further tornadoes may touch down in the continuing stormy weather and MetService has issued a Severe Thunderstorm Watch for the North Island including Coromandel Peninsula, Waikato, Bay of Plenty, Rotorua, Taupo, Gisborne and Hawkes Bay. The alert states:
The Science Media Centre has collated commentary from experts on the unfolding weather situation.
Dr James Renwick, Assoc Prof of Physical Geography, Victoria University of Wellington, comments:
Is this a pattern, part of a larger trend related to climate change and increasingly extreme weather?
“Damaging tornado events are associated with localised severe thunderstorm activity — but analysis of weather records does not show a pattern, nor are there trends obvious in tornado occurrences.
“These events strike at random from time to time, but they are very localised and sporadic and are not obviously tied to trends in the large-scale climate. At this stage, we have no indication that tornado occurrences will become more or less frequent in future.”
Dr Jim Salinger, climate scientist and visiting professor at Stanford University, comments:
“On the New Zealand front we have about 30 tornadoes a year, mostly small in comparison to those in US. These are largely seen in northern New Zealand down to Taranaki, and west coast of the South Island. You need the weather systems conducive for tornadic development for a start…and more westerlies over New Zealand will give this situation. So ultimately we may see more energetic westerly storms. The future of tornadoes is unclear…but indications are that they could be a bit stronger.
“The bottom line is that with a warmer atmosphere there is more water vapour in the atmosphere, so as it condenses into cloud droplets more energy will be released providing more energy for storms. At the same time any precipitation is heavier. This has been seen in recent US tornado seasons.”
Dr Marwan Katurji, Lecturer in Meteorology, University of Canterbury, comments:
“The North Island, especially the west coast, is more vulnerable to westerly and northerly winds that are associated with weather fronts. Warm moist air from the warmer Tasman Sea carries within it embedded thunderstorms. When the air hits land it interacts with the topography to create convergence zones and the wind speeds are higher in these areas and the storms get more severe in this case.
“The Auckland region is one of the hot spots for this activity which promotes tornadoes, though Taranaki region is the record holder.”
Dr Richard Turner, Meteorologist, NIWA, comments:
“fatalities associated with tornadoes are rare in New Zealand, with the most recent cases being the Albany tornado last year, which killed 1 person, and a tornado near Waitara in August 2004 which killed 2 people.”
“Auckland is hit by a tornado on average less than once per year, but there is considerable variability from year to year with some years getting none,” says Dr Turner.
“In New Zealand most tornadoes are associated with pre-frontal squall lines – bands of thunderstorms embedded in strong unstable pre-frontal northwesterly flow.”
“The thunderstorms have very strong updrafts and if these occur in an environment in which the wind directions rotate as the air rises, the updraft can start to spin and a mesocyclone can form. It is from these mesocylcones, that can be as little as 1-2 kilometres across, that tornadoes are spawned.”
More information can be found on the NIWA page, Extreme weather – winds and tornadoes.