A brief history of Tropical Cyclones
(and a “Weather Alert” from Stradbroke Ferries)
Ah.. Summer in Queensland. When a young mans thoughts turn to almost anything other than rain, cyclones and destruction.
But perhaps not such a good idea, especially this week. As Tropical Cyclone Oma bears down, this not-young man (61 years old) has his thoughts cast backward in Time (thanks Steven Hawking).
There have been several Severe Tropical Cyclones of note, a small handful of which I was witness to.
And at the starting gates is 1974 and Wanda. A Cyclone named Wands – NOT an Fish called Wanda, though you may have thought otherwise if you experienced firstly the incessant downpour which heralded the infamous 1974 flood. Possibly the first (along with Darwin’s Tracey) prime time weather event. Entire suburbs went under.
My wife’s house was one of those, in the bend of Fig Tree Pocket, it kept creeping up and up to 60 Cm in the house. Which was (as was so often the case) due to stormwater backing up. Considered lucky, her family had an upper floor to evacuate their and their neighbor’s furniture to; they were evacuated to relatives’ homes by speedboat.
For myself – vivid memories were of my Dad’s workplace. He was the general Manager of the RSPCA, then located at Fairfield – some four or five metres underwater.
All the animals needed evacuating, so were moved (Noah’s ark style) to the Royal National’s Exhibition grounds.
All hand’s on deck was the cry.
I had to see to the cats. The all had to be put down, as they went crazy in their cages as the water rose. Not possible to do anything else with it, I guess close to a hundred cats and kittens. The RSPCA had a machine for this purpose, which was used. Safe for humans and painless for animals.
Next in my memory was Nancy 28 January – 8 February 1990 Tropical Cyclone Nancy
here is the BOM Summary. I just remember being glued to the TV watching for any indications we were to go through another “Wanda”. Fortunately, it took one look at Pt Lookout on Straddie sand scarpered away.. Leaving a cloud of hot air behind as everyone breathed out a cumulative sigh of relief .. Missed me by THAT much Chief – as Maxwell Smart would say.
Summary from the BOM
During the later part of January, the monsoon trough became active over the southwest Pacific and two depressions were spawned along it. The second depression, which later developed into cyclone Nancy, developed from a cloud cluster over the Coral Sea near 18.3°S 156.0°E on 26 January. From this position, the depression headed equatorward along a parabolically curved track. An upper level trough eventually amplified in the vicinity of the depression and set up good outflow channels for further development.
By 0001 UTC, 31 January, the depression had gained tropical cyclone characteristics near 15.0°S, 158.0°E. The convoluted nature of the upper level trough helped steer Nancy southwards. When it was located west of northeast New Caledonia, the cyclone veered southwest and followed a course towards Brisbane. Nancy reached peak intensity at 0300, 1 February near 24.7°S, 158.2°E with a maximum winds of 100 km/h and central pressure of 975 hPa.
On the 1 and 2 Febrary, Nancy ‘s progress just off the Queensland coast near Brisbane was slow and irregular. Heavy rain (up to 530 mm in 24 hours, 132 mm in three hours) occurred between the coast and coastal ranges south from Brisbane causing flash flooding in which four people were drowned.
On its trek southwards, Nancy gradually weakened and by 4 February it finally became an extratropical low. Surface reports and satellite data over the southern Tasman Sea demonstrated that Nancy’ s structure
still contained a significant low pressure centre for two days after this date. The remains of the former
cyclone dissipated west of central New Zealand on 8 February.
That was Nancy’s bid for fame.
In 2004 we had another contender in the wet welcome stakes, Linda:
Summary from the BOM
Tropical Cyclone Linda
28 January – 1 February 2004
Linda was a small Indian Ocean tropical cyclone passing to the west of Cocos Islands and briefly reached category 2 intensity on 31 January before weakening rapidly as it moved further south.
A weak low emerged from within the monsoon trough late on 28 January to the northwest of Cocos Islands and
moved to the southeast. The system was hampered by moderate easterly shear in excess of 20 knots. A Quickscat pass on the morning of 29 January identified strong winds associated with convection but these are probably overestimated being in a rainblock perpendicular to and near the centre of the swathe and the subsequent Quickscat pass showed maximum winds only to 30 knots and satellite imagery showed an absence of deep convection near the centre and certainly an absence of banding in the convection.
But what about 2011? I hear you say. I had not forgotten 2011. I had recently taken on the ownership if ‘Bay Island News’. I also had a sister in Law at Murphy’s Creek. Yes, THAT Murphy’s creek which was effectively wiped out.
I featured my exploits in an aborted attempt to reach Murphy’s creek in the February edition of Bay Island News.
But, true to Murphy’s Law, I cannot find any images of the epic trek, not the in; land sea (well, that’s what it looked like) which was Lake Somerset. Pity, I know I have a copy somewhere – just can’t find them, ah well.
It wasn’t a cyclone anyway..
Which brings me to the final topic, What is a Cyclone?
Well, again I borrow from the experts, BOM.
What is a Tropical Cyclone?
Tropical Cyclones are low pressure systems that form over warm tropical waters and have gale force winds (sustained winds of 63 km/h or greater and gusts in excess of 90 km/h) near the centre. Technically they are defined as a non-frontal low pressure system of synoptic scale developing over warm waters having organised convection and a maximum mean wind speed of 34 knots or greater extending more than half-way around near the centre and persisting for at least six hours.
The gale force winds can extend hundreds of kilometres from the cyclone centre. If the sustained winds around the centre reach 118 km/h (gusts in excess 165 km/h). then the system is called a severe tropical cyclone. These are referred to as hurricanes or typhoons in other countries.
The circular eye or centre of a tropical cyclone is an area characterised by light winds and often by clear skies. Eye diameters are typically 40 km but can range from under 10 km to over 100 km. The eye is surrounded by a dense ring of cloud about 16 km high known as the eye wall which marks the belt of strongest winds and heaviest rainfall.
Tropical cyclones derive their energy from the warm tropical oceans and do not form unless the sea-surface temperature is above 26.5°C, although once formed, they can persist over lower sea-surface temperatures. Tropical cyclones can persist for many days and may follow quite erratic paths. They usually dissipate over land or colder oceans.
Most of the northern coastline of Australia is covered by the Bureau’s weather radar network. For real time images and radar information, see: www.bom.gov.au/weather/radar/
I could not finish this article without reference to Stradbroke ferries expected announcement of restricted services.
They announced this today, Wednesday 20th Feb.
I’m a cynic.. sorry, but that’s the way I am. This cyclone is, at the time pf writing 1,000 kilometres from the coast.
HERE is their alert in full.
In effect from 21st to 24th . The damn thing isn’t even predicted to hit the coast until the 25th, maybe, perhaps…
At this stage, we are discouraging any non-essential travel from Thursday 21st February 2019 (afternoon travel) to Sunday the 24th February 2019.
Personally, without any facts stated to validate their reasoning I think I can be a bit cynical.
A more reliable source is the BOM, read it HERE .