Tornadoes in Western Australia
Tornadoes in Western Australia. © Ira Fehlberg 1998
It is a popular notion that Tornadoes do not occur in Australia or if they do that they are merely Willy Willy's. This not helped by the media who often describe them in reports as " a freak storm " or " mini Tornado " when in fact it was a fully-fledged Tornado. Tornado research in Australia is really only in it's early stages and several Storm-chaser's are now in touch with each other around Australia. I recently spoke with Barry Hanstrum of the Severe Weather branch of the WA Weather Bureau and he told me that Tornado occurrences had trebled since they started looking for them. Previously they only recorded a Tornado if someone phoned them up and reported one down. Similarly in England only 60 Tornadoes had been recorded up until 1950. But since the forming of TORRO (a British Tornado research program) in 1974, 400 new Tornadoes have been documented in the 22 years since.
Tornadoes in Western Australia are a mixed bunch. Records have been kept since white man has been here but records from 1955 on are considered to be a more accurate source. This is due to the fact that in years prior to 1955 a tornado was possibly recorded when in fact it was just a severe wind squall, microburst or a downburst of some kind. These day's tracks are now investigated to make sure it was in fact a tornado. Certainly there are definite sightings of tornadoes before 1955 but I have not included them in this study so that I could get a more accurate representation of the true number of events.
The first ever-meteorological study of a tornado in WA was only in 1954 by Volprecht of the Collie tornado. Since 1954 approximately 150 Tornadoes have been recorded. Just two weeks ago there were two separate reports of raining fish in this state. Obviously two unseen tornadoes passing over a dam or creek. However no tornadoes were reported. Due to our sparse population many tornadoes must go unreported.
Of the 150 tornadoes recorded Perth and its surrounding area down to Mandurah accounts for 55 or one third of the states records. We know that Perth doesn’t take up one third of the state's land mass. So obviously with the large population density in Perth tornadoes damage does'nt go unnoticed. Studies in the US show that a population density of 100 to 200 people per square mile is needed to gain accurate tornado numbers. The 1986 census showed that the SW of WA has a population density of 10 people per square mile. The only areas, which have the required density to gain accurate numbers, are the Perth, Mandurah and Bunbury areas. If you take the number of tornado occurrences in these areas and divide it by the number of square miles you obtain a figure for tornadoes per square miles. Then apply this figure to the remaining square miles from Busselton to Lancelin and a figure of 6 tornadoes a year is gained. This would equate to 250 tornadoes for this section of coast for the years 1955-1996. Little alone the rest of WA. I would conservatively say that this figure is more likely to be around 400+ tornadoes for WA since 1954.
Tornadoes in WA basically go into two groups, winter tornadoes (April through to end of September) and summer tornadoes (November through to end of March). Winter tornadoes account for 75% of the total and are confined mostly to the coastal areas from just north of Perth down to the inland of the southwest land division. Winter tornadoes are most common in June and July and are formed from severe cold fronts, which generate thunderstorms. There are many types of winter tornadoes and not a lot is know about how they form. Partly due to the fact that most US tornadoes are summer tornadoes formed in supercells and this is where most research is done. Although Barry Hanstrum and Chuck Doswell are currently working on an international paper on cold air tornadoes. Winter tornadoes also seem to account for the most severe tornadoes. The most severe winter tornado swept through the Lyalls Mill area near Collie early in the morning on the 6/4/60. The tornado track was 30 kilometers by 240m wide through dense Jarrah forest and carried wind speeds of an F-3 tornado. The Jarrah trees uprooted took the local mill one-year to clean up. Mind you F-3 Tornadoes have occurred here in the summer.
Summer tornadoes are usually north and east of Perth with the highest concentration of events around Northam, Goomalling, Bindoon and York area. But they have been recorded as high up as Port Headland. In fact a nice one with a purple funnel was on the ground right in front of the weather bureau in 1975. Tornadoes occur around this area due to the summer type weather pattern of deepening troughs developing down the coast added to a mid level trough, storms then form inland over the warmer air masses. Check the temperatures on any day in summer and you'll see that Northam is always much hotter than Perth. Summer is better for chasing as the storms move slower and visibility is good but generally numbers are less (25% of the total).
Mandurah seems to be our tornado capital with a remarkable 9 tornadoes in the space of 33 years. This is directly on the town of Mandurah, if you include the area about 20k's north (i.e. Safety Bay, Shoalwater Bay and Rockingham) the figure is 18 in 33 years! With 7 of these being either F-2 or F-3. This is a higher density figure then almost any other place in the world!
As far as outbreaks go WA has had its fair share. In fact we have has 12 days since 1960 in which there was 2 tornadoes on the same day, 6 days with 3 tornadoes 2 days in which there was 4, one day last September in which there was 5 and on the 6th of June just gone we had 7 tornadoes!! 1995 is the best year on record with 15 tornadoes for the whole year. Ten of these were in one month and of those ten, five were in just two days. Certainly respectable figures.
As far as the strength ratings go this is very hard to ascertain, as most records say nothing about damage. We have certainly had several F-3 tornadoes (at least ten) but whether or not we have had any F-4 / F-5 is unknown.