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Tuesday 20 March, 2007
Rangers at Kakadu National Park had a lucky escape when a powerful tornado carved a trail of destruction through forest near the Mary River Ranger Station two weeks ago.
Two unoccupied caravans were totally destroyed and many trees were snapped and felled around the rangers’ houses and office. Park ranger Rob Muller said that the noise of the spinning wind was loud like an industrial machine and could be heard for at least 10 minutes as the tornado approached in the dark, then moved slowly away.
Bureau meteorologists surveyed the area last week. The centre of the 3-kilometre long damage swath passed within a few hundred metres of the Ranger Station. In the worst affected areas, hardwood trees such as eucalypts and ironwoods were uprooted or torn apart. In many instances large, mature trees were reduced to de-barked and de-foliated stumps with only some larger branches remaining. Curved trails of debris provided stark evidence of the clockwise spiralling winds around the centre of the tornado. The caravans and a washing machine were lifted and tumbled over distances up to 100 metres by the destructive winds in the 300-metre wide tornado.
Severe Weather Meteorologist Greg Browning said that the tornado formed during the evening of March 1st under a line of thunderstorms near a tropical low over Arnhem Land. This low caused record-breaking rainfall that flooded the Oenpelli and Adelaide River areas, then developed into Tropical Cyclone George a few days later. Mr Browning said that tornadoes occur infrequently in the tropics, but atmospheric conditions favourable for rotating thunderstorms sometimes occur on the periphery of tropical lows and cyclones.
The Bureau estimated that winds in the tornado were between 230 and 270 km/h, based on an assessment of damage to trees and caravans using the five-point Fujita Scale. This scale is used to rate the intensity of tornadoes by the US National Weather Service.
The Bureau of Meteorology in Darwin issued Severe Weather Warnings for the first time during this tropical low, alerting of possible damaging wind gusts and heavy rain leading to flash flooding. This recently introduced service provides Territorians with warnings for severe weather caused by intense tropical lows, decaying tropical cyclones and strong monsoonal winds.
Fig 1. Tornado damage to eucalyptus forest at Mary River Ranger Station
Fig 2. Tornado damage to caravan containing equipment at Mary River Ranger Station
Greg Browning, Bureau of Meteorology, Darwin, (08) 8920 3808, e-mail: ntsevere@bom.gov.au
Rob Muller, Mary River Ranger Station, Kakadu National Park (08) 8975 4578, e-mail: rob.muller@environment.gov.au
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