Home' Horizons : April-May 2010 Contents inland they can bring heavy rainfall
to the Goldfields, the Eucla and the
South West Land Division.
While most cyclones occur
in WA's north, certain weather
patterns can cause them to
For example, if a frontal system
moves up from the south towards
WA while a tropical cyclone is
active, there's a chance the front
may "capture" the cyclone and drag
it southwards while it's hovering
in waters west of the State. These
were the circumstances that led to
Cyclone Alby hitting WA's south in
1978, killing five people. Albany bore
the brunt of the cyclone, recording
winds of up to 150km an hour.
Severe thunderstorms are also
a destructive force in WA. They
can happen anywhere in the State,
but most typically through the
Eastern Wheatbelt, Goldfields
and Southern Coastal areas during
summer. Thunderstorms develop
when warm, humid air near the
ground receives an initial upward
push from converging surface
winds and rises rapidly in an
Winter cold fronts can also
bring strong winds, heavy rain, hail
and cool season tornadoes, also
known as twisters, willy willys and
cock-eyed bobs. These are the
most rare and violent thunderstorm
For a cool season tornado to
form there needs to be rain or
thunderstorms on a day when the
winds change significantly with
"Typical tornado paths are
around 50 to 150m wide and several
kilometres long, with wind speeds
as powerful as a tropical cyclone,"
Bureau of Meteorology (WA) Senior
Forecaster Neil Bennett said.
"They often occur in outbreaks
so that every few years we can see
five or six tornadoes leave a trail of
ripped through a suburb of
Mandurah, 72km south of Perth,
demolishing eight houses and
damaging another 100.
In 2005 a series of tornadoes
hit Bicton and the southern
suburbs of Perth.
"These tornadoes involved
approximately 6000 claims being
lodged with RAC Insurance,
which is a significant number.
Some claims were in excess of
$100,000," Mr Selfe said.
Tornadoes are most frequent along
the coastal strip from Lancelin,
110km north of Perth, to Mandurah.
The coastal city of Rockingham,
38km south of Perth, is a
well-known tornado hotspot.
"There does appear to be
a tornado alley through the
Rockingham area where we
receive a large volume of claims,"
said Mr Selfe.
According to Mr Bennett there
may be more twisters in the
Rockingham area because of the
coastline orientation. Here the
coastline juts out, and combined
with Garden Island there may
be some change to surface flow
that helps tornado formation,
however there has not been a
study into this.
Although the number of
tornado reports has increased
over time, there's no evidence that
the actual number of tornadoes
has increased. The larger number
of tornado reports is due to the
spread of population and increased
"It is likely that the impact of
cool season tornadoes will increase
given the development along the
coastal strip," Mr Bennett said.
The Bureau of Meteorology is
able to issue warnings up to six
hours before a tornado hits and
give plenty of notice for other
impending bad weather.
As well as this, there are a
number of measures you can take
to protect yourself during the
These include cleaning the
guttering, trimming branches
away from the home and
securing loose objects and garden
As a result of her terrifying
experience, Mrs Henderson has
removed a number of trees that
were close to her house, and
has regular termite inspections
to ensure all the trees on her
property are healthy.
"I also double check the
insurance premium prior to winter
to make sure we are paid up and
covered for building damages,"
How storms form
Differences in the airflow below 500m cause
rotation that gets swept into the updraft in
ms. Tornadoes can form if this rotating column
contracts to spin up.
Keep your home and car
safe from storms
✔ Check and repair roof cover and guttering
✔ Clean and remove all leaf debris from roofs and guttering
✔ Trim tree branches away from homes and electric power cables
✔ Secure and tidy yards, patios and balconies from all loose
objects, including sheds and garden furniture
✔ Check your car battery, which can fail following extreme
changes in temperature
THE last two years appear to have shown a trend in greater claim
numbers for storm damage.
2006 -- 2007
7,262 claims, cost $6.4m
2007 -- 2008
10,338 claims, cost $11.9m
2008 -- 2009
13,450 claims, cost $15.3m
PHOTOGRAPHY: GETTY IMAGES, ISTOCKPHOTO.
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