The Brisbane Tornadic Supercell and other Severe Thunderstorms across SE Qld
Tuesday October 13, 1998storm report
From 9am thunderstorms started to develop over the Border Ranges SW of Brisbane and also on the hills to the NW. By 10am the thunderstorms were well established and the atmospheric conditions pointed to the severe potential later in the day. A trough was located just south of the Qld/NSW Border with the parent cold front over Central NSW. Keeping it simple, the air over the SE Qld region was extremely moist and unstable, and the fact that early thunderstorm development occurred before the heat of the day could play a part was substantial. In Brisbane, the conditions on the ground were 'storm friendly' with humidity (%) in the high 70's and a temperature rising which would ultimately reach a sultry 32C. The wind during the morning was light to moderate NW which freshened markedly during the early afternoon and even turned more WNW'ly before a seabreeze developed. Apart from the distant cumulonimbus (Cb) the sky was partly cloudy with a mix of low and mid level cloud including another signature of a lively thunderday - altocumlus castellanus (ACCAS).
The first town that was severely impacted by storm activity on this day was Pittsworth, a half hour drive southwest of Toowoomba at about 11am. This storm built up suddenly over the Darling Downs and soon hail up to 4.5cm was falling on the town, helped along by destructive winds. Power poles and trees were blown over causing some damage to houses and cars. For safety reasons, those areas that didn't lose power were blacked out because of the lives wires on the ground. It was only still early in the day and much more was to come.
The 11:30 radar images showed at least 3 hailstorms lined up on the Border Ranges including one that was ripping through the town of Warwick. At least 50 houses were damaged including around a third of which were unroofed. Hail to 3cm fell also and despite some reports no evidence of a tornado was found as damage initially appeared to have been caused by straight-line winds only. The town's showground grandstand was unroofed but because of an upcoming rodeo, it will be fixed promptly. Winds probably reached 130km/h at the height of the storm.
During the next couple of hours countless thunderstorms developed over SE Qld with a high percentage containing hail at certain stages. By looking at radar loops of the storms, the cell that was to affect Brisbane formed out of a strong cluster to the NW of Warwick between 12.50pm and 1.30pm. It is very hard to tell though because of the short spacing between the multiple storms. Just before 2pm thunderstorms started to move in from the Eastern Darling Downs and it was like the region was being attacked from two sides.
Sometime after 2.15pm something happened to the storm that was to severely affect Brisbane. With gusty WNW or NW winds blowing, the fresh NE'ly winds of the seabreeze front suddenly moved in and within half an hour the thunderstorm intensified sharply to the SW of Ipswich. It seems as if the seabreeze front helped start the storm rotating with the development of a mesocyclone. At around 3pm the storm 'side swiped' Ipswich and started to pick up speed towards Brisbane. The 3.20pm radar image picked up a 'bow echo' amongst very intense precipitation including large hail as it had just started to affect Brisbane's western suburbs. The now supercell thunderstorm then moved over Brisbane's southern, CBD and inner northern suburbs with a bang.
Residents watching the storm arrive were awe-struck by the ominous gust front rushing towards them. A man watching from a hill at Clayfield saw numerous 'power flashes' as dozens of power lines came down, before he had to make a run for it. As it blasted through, there were numerous accounts of the ferocity of the winds. One elderly woman at Hendra was watching the storm from her veranda when a piece of timber grazed her cheek before smashing through the windows landing in the lounge room. A group of people couldn't believe their eyes when a truck was blown over. In another instance a bus was blown sideways across the road incredibly without tipping over. Many streets in the Central Business District were littered with trees, powerlines, crashed cars and large sections of roofing iron. Some residents had believed there was something 'very different and scary about this storm'.
They were right about that. As the supercell displayed a tell-tale hook echo at 3.40pm a funnel cloud dropped half way to the ground in Fortitude Valley. Though the actual funnel did not reach the ground, debris was clearly seen on amateur video flying around in a definite rotating motion. On the video, dust and pieces of roofing iron were flung into the sky and some buildings were completely unroofed by it. There has been some hesitancy to call it a tornado but the author believes it was the city's first since Christmas Eve, 1989. It was quite light meaning that it occurred close to the back of the storm and no rain was falling during the event. We know that a funnel cloud does not have to touch the ground as long as debris is noticed on the ground. Many residents at different parts of the city reported the rotating mesocyclone associated with this severe supercell but of course a report will be written by the Brisbane Weather Bureau and perhaps then we'll have a definite answer as to whether it was a tornado. Again the author does believe it was a brief tornado, of probably F0/F1 intensity.
The bulk of the damage however was caused by strong microbursts. The maximum gusts recorded during the storm were 70kn at Manly (130km/h) and 64kn (117km/h) at the Brisbane Airport , but as is usually the case, the areas that experienced the most damage had no anemometers. Wind estimates in these areas would be no higher than 150km/h. In those areas some accounts of residents were described in The Courier Mail (14/10/98 ) the day after:
It was like a tornado, "he said. "This whirlwind picked up everything, went across the road took off the roof, turned a truck over and then turned around. Table and chairs went into the creek, plates were flying like someone was playing frisbees." As said by the owner of a restaurant at Breakfast Creek after he was dining outside when the storm came.
When a reporter asked an elderly lady about her patio (balcony), she said: "Yes, I was in the lounge and then it came and I went to open the back door to have a look at the patio...and it wasn't there".
There were obviously many more accounts of what happened during the onslaught. The Castlemaine Perkins warehouse in Hendra was badly damaged. It was unroofed and thousands of dollars worth of stock was destroyed. At Newstead, the roof of the Smith Family Charity was blown off, destroying all clothes inside - which means bad news for the needy families over Christmas. Other storing sheds and factories probably not built to withstand very strong winds were unroofed and badly damaged. Whole apartment blocks were unroofed leaving many people homeless. At the Allan Border Oval in Albion, the Victorian and Queensland teams were sheltering in their dressing sheds when the Victorian team's roof blew off. They hurriedly all crammed into small toilet blocks - wearing batting helmets.
For many shocked residents in the inner northern suburbs, it seemed like a recurring nightmare. On the 18th of January 1985, another supercell tore through damaging about 20 000 buildings - which is still Brisbane's costliest ever thunderstorm at >$350million (in 1998 dollars) damage. Those suburbs hit hard in the 1985 disaster like Hendra, Fortitude Valley and Newstead appeared to be 'ground zero' for this latest severe thunderstorm. At this stage total damage just in Brisbane is at least $35million. This would put it amongst the most costliest storms in the city's history. Perhaps the storms of 04/11/73, 16/12/80 and of course the 18/01/85 storms would be ahead of it in 1998 dollars. Damage still has to assessed for other parts of SE Qld that suffered damage.
The radar showed over 15 distinct severe thunderstorms - three of which appeared supercellular. Those areas that experienced severity from these storms included Pittsworth, Warwick, Boonah, the Glass House Mountains, Brisbane, Yarraman and Gympie. The most prevalent component of these storms was hail, and mostly the reported size was 3-4cm or about golf ball size. At Cannon Hill in Brisbane a Bureau of Meteorology staff member reported hail at 4cm on average covering the ground with the biggest stone measured at 5.1cm. In the rural areas such as Yarraman and Pittsworth the golf ball hail caused inevitable crop damage but in the city while golf ball hail was relatively widespread over the hardest hit suburbs, hail damage was minor and confined to shallow dents on cars and a few broken windows. If the hail was just a little larger the total damage may have rivalled the great 1985 storm - but luckily that did not eventuate. At the height of the storms in Brisbane, just over 50 000 premises were left without power. Some isolated areas had to wait over 24 hours to be reconnected as literally hundreds of downed powerlines and some power poles had to be fixed.
Soon we'll know the true cost of all the severe thunderstorms that struck SE Qld during the 13th of October, 1998. The entire event will go down in history as one of the liveliest thunderdays that has ever occurred in the region. When strong storms started developing mid morning over the Border Ranges many people knew that something MAJOR was going to happen, and they were right. Over the course of the next ten hours or so over 15 severe thunderstorms were recognized by radar. The storm that affected the capital city was the most severe. It was a supercell thunderstorm which roared through with winds around 150km/h - either caused by microburst or the tornado that occurred in Fortitude Valley. Although many buildings were damaged, we were very lucky that only minor injuries resulted.
Click here to read an account of the day by Anthony Cornelius - on ASW
