Wednesday, 17 August 2016

Dubbo Tornado - 24 August 2015

Tornadoes are a regular if uncommon occurrence in Australia. When events do occur in areas far from our nation’s metropolitan centres those with the expertise to record and analyse the damage left by these event are significant distances from the affected area. Additionally the resources available to meteorological organisations interested in studying these phenomena are limited.

The tornado that impacted areas east of Dubbo on 24 August 2015 is arguably the most well observed and recorded tornadic event in Australia’s history. Countless photos and multiple videos captured the event in progress and the damage left in its wake. Many of these images were published by news websites and individuals on social media platforms.

The event data available for the event in the Severe Storm Archive records maintained by the Bureau of Meteorology is incomplete and is as follows.

Tornado ID: 1282, Date/Time: 24/08/2015  6:00:00 UTC, Latitude: -32.2484, Longitude: 148.6012, Nearest town: DUBBO, District: Central Western Slopes and Plains, LGA: Blank, State: NSW, Postcode: Blank, Source: SES, Station number: Blank, Duration: 0, Min speed: 63, Max speed: 117, Fujita scale: 0, Path length: 0, Path width: 0, Path direction: 0, Damage total: Blank, Insurance payout: Blank, Number of deaths: Blank, Number of injuries: Blank, Comments: Jonny from SES called with report of a tornado at Dubbo around 5-5:15 PM. Police got some more calls with reports of partial roofs off houses and very strong winds. Jonny relayed this info through. Possible footage too. No GPATS over Dubbo at this time but there were a couple near Gilgandra. Tornado
This entry - as with many in the archive - is vague. The wind speeds in this tornado record are the generic minimum and  maximum wind speeds for a tornado rated F0 on the Fujita Scale. It is clear no damage survey was completed, as no path details have been entered. Therefore no rating was made based on surveyed damage.

Synoptic Summary

On the 24th, a complex low pressure system produced widespread thunderstorm activity as it crossed New South Wales, before intensifying into an East Coast Low as it tracked off the New South Wales coast on the 25th (MWR - Australia - Aug 2015, p. 5). Thunderstorm activity was widespread across northern and eastern New South Wales, and parts of the Darling Downs and Granite Belt in Queensland on the afternoon of the 24th, with 2-3 cm hail reported in many areas, including Sydney, the Blue Mountains, the Hunter Valley, and Boggabilla near Goondiwindi, as well as flash flooding that occurred in the Sydney CBD, with 22.2 mm of rain in 11 minutes at Observatory Hill on the evening of the 24th (MWR - Australia - Aug 2015, p. 3).



The Skew-T sounding available from Moree at 10:00 AM (23/08/2015 23:00 UTC) reveals an increased amount of shear (turning) in the lowest portion of the atmosphere.

Temperature, dew point, rainfall (weatherzone.com.au)
10m winds, gusts, pressure (weatherzone.com.au)

The 24 hour graph of observations for the 24th (EST) at Dubbo Airport show that the tornadic event was accompanied by a drop in pressure. The updraft that produced the tornado passed a few kilometers to the north of the airport about 10-20 minutes before the tornado touched down. These observations also confirm what is shown in all photographs and video that the tornado occurred a significant distance from any precipitation associated with the storm producing it, a low-precipitation (LP) supercell.

Remote Damage Survey

While no on-the-ground survey was carried out, sufficient evidence was published online to carry out a remote survey for the event. As previously demonstrated, remote damage surveying techniques using open source data mining of social media for post-disaster damage assessment are well recognized (Shergold, 2016 para. 4). The data available for this event offers another unique opportunity to explore the potential of remote damage surveys that can supplement on-the-ground resources available.




The conclusion that can be drawn from the remote damage survey is that this tornado was of at EF1 strength, producing damage consistent with winds 135-175 km/h over much of its 7 kilometre damage path. The maximum path width was at least 100 metres near the end of the documented path, at the same location where the most significant damage was recorded. This damage to a well constructed outbuilding (SBO) and  numerous mature trees suggest the tornado produced an area of EF2 damage in which the EF scale damage indicators provide good contextual confirmation for a mid-range EF2 rating. The footage captured as the tornado reached the mature climax of its destructive power demonstrates that the tornado was strong (Ross Sawtell, 2015).




Event Summary

Start Date/Time: 24/08/2015  6:00:00 UTC
Start Latitude/Longitude: -32.23358, 148.66879
Duration: 15 minutes
Maximum wind speed: 190-200 km/h
Enhanced Fujita Scale: 2
Path length: >7000 metres (7 kilometers possibly up to 10 kilometers).
Maximum Path width: >100 metres
Path direction: 310 degrees
End Date/Time: 24/08/2015  6:15:00 UTC
End Latitude/Longitude: -32.27793/148.71993


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