ISOLATED SEVERE THUNDERSTORM IN THE BAYSIDE SUBURBS OF BRISBANE
OCTOBER 20, 1999

A few large showers had developed during Wednesday afternoon (20th of October, 1999), but unfortunately nothing eventuated from it.  During the evening, a large band of showers and thunderstorms effected the QLD central coast area, but there were no signs of any development in SE QLD.

At around 11pm, some showers started developing, predominantly over Brisbane's northside suburbs.  Some of these showers were quite intense, but generally rather small, rain rates were around 20-40mm/hr.  At approximately 11:30pm, a large shower formed just SW of Redcliffe, this continued slowly drifted eastward.  I didn't think twice about it, it just looked like some one was going to get a heavy shower with some nice totals.  However, remarkably the shower split into two, with one shower (the weaker one) moving northwards before quickly dissipating, and the other (stronger one) moved southwards.  The stronger shower eventually became a small thunderstorm, with rain rates between 40-100mm.  I personally was getting excited, not because I thought I'd get a great thunderstorm, but simply because it looked like that I was going to get a nice heavy downpour, with the odd flash of lightning and rumble of thunder if I was lucky.

As the cell continued southwards, it continued to gain intensity, soon rain rates were at a maximum on radar - in excess of 100mm/hr!!!  The airport and surrounding areas were the first to feel the full brunt of the thunderstorm at approximately 12:30am, with the BoM notes indicating an incredible 70mm of rain falling in 15 minutes!  I could observe some infrequent lightning to my north, about 2-3 strikes a minute, it didn't seem too active from where I was, but after completing a Damage Assessment Survey on the area, residents informed me otherwise.  Lightning and thunder was frequent, and at times almost continuous.  "The winds were incredible...", "...it was terrifying...", "...she was an absolute doozy mate..."  The damage strip was narrow, I visited a suburb just south of the airport, where there was debris from plants and trees strewn all over the road.  I was told that a fair bit of the debris had already been cleaned up by a city-council sweeper.  None the less, there was still a fair bit of damage to plants and trees.  No shortage of large branches being snapped off, and a few trees were also down as well.  The winds were unusual in this thunderstorm, due to the abnormal direction it moved in (SSE), by looking at damage patterns it was clearly evident that the predominant wind was NE'ly.  I observed a field of grass, that while not completely flattened, was certainly noticeably wind swept.  I had never seen this before.

While talking to some residents, one resident had part of her cladding removed from her house, another house had their windows broken by hail and winds.  Most residents seemed to have received water damage, when the gutters could no longer cope with the intense rain, and water poured into their ceilings.

The airport area was worse hit, after it passed through the area it following the coast line, moving SSE/SE.  It narrowly missed me by a few kilometers.  The cell itself was very small, but also very intense.  I also went out to the Lytton/Wynnum area to observe any damage.  The damage here paled into insignificance to the airport damage.  Lots of leaves, small branches down in some areas, but nothing like the airport.  There was also the odd tree down, they were very weak trees only.  There was still an incredible amount of water lying around in both the Lytton/Wynnum area and the airport.  Not surprising given the enormous amount of rain that fell.  Lytton recorded 42mm of rain, and Manly (further south) recorded 36mm of rain.

Conditions for thunderstorms were far from favorable that night, let alone severe thunderstorms.  CAPE was only 117, although SRH was unusually high at 120, with a maximum at 142.  The cell maintained maximum intensity on radar for one and a half hours.  Given the splitting mechanism, unusual strength and longevity of the thunderstorm, combined with the high SRH, one has to wonder whether this was just an ordinary thunderstorm.  But I do believe that this is just a reminder, that we can never turn our back on nature, nor try and define nature in a set of 'feeble man-made rules,' as it is just simply too complex and deep for our limited minds to ever begin to comprehend.

Rainfall totals in the 24 hours to 9am Thursday, October 21

Lytton - 42mm ; Manly - 36mm ; Redcliffe - 45mm ; Brisbane Airport - 73mm ; Strathpine - 40mm Toombul - 23mm ; Boondall - 45mm