Home' Afloat : AFLOAT May 2016 Contents 54 AFLOAT.com.au May 2016
by Malcolm Riley*
*Mal Riley is the Media and Communications
Manager for the Bureau of Meteorology in
Hobart. He has worked in meteorology for 40
years. He is a skipper of the tall ship The Lady
Nelson and a keen sea kayaker.
Afloat reader Edwina Hession of
Grays Point NSW asked if the
“ tornado-like” event at Kurnell last
December was a tornado or a waterspout
It was a tornado.
On Wednesday December 16 last year
severe storms formed and moved across
the Sydney area causing damage at Kurnell.
Severe storms and how they can form have
been discussed in Afloat in recent months
and those articles can be viewed online in
theFeb’15,March’15 andJuly’15 editions.
Severe storms can bring heav y rainfall,
flash flooding, large hail, damaging wind
gusts and occasionally tornados.
This event can be used as an example
of how the Bureau of Meteorology warns
the community about the possibility of
severe thunderstorms. Firstly it helps to
know that the Bureau has a two tiered
graphical warning system. A graphical
warning showing broad areas of potential
severe storm development is issued for all
The graphical warnings that identify
individual storm cells and their predicted
movement are only provided for the
cities and adjacent areas around Sydney,
Brisbane, Melbourne and Adelaide. All of
Australia is also covered with text warning
of areas of likely severe storm activity.
Thunderstorms first appeared on the
Sydney area forecast on Friday the 11th for
Wednesday the 16th. On Tuesday afternoon
(15th) the first indications that expected
storms for the next day would possibly be
severe were published: “ Thunderstorms likely,
The first severe thunderstorm warning
was issued at 07:51 on the day of the storms.
This warning highlighted the area where
the development of severe storms was
possible: in this case coastal and adjacent
inland areas from Moruya to Gosford.
The warnings were updated numerous
times during the morning, warning for large
hailstones, heavy rainfall and damaging
winds and highlighting the areas that were
likely to be affected. When the storms were
identified on the radar their locations and
the predicted movement of the individual
storms cells and areas of immediate threat
were added to the graphical warnings.
The warning issued at 08:30 increased
the wind from damaging to destructive
winds. Damaging winds refer to gusts from
90 up to 124km/h and destructive winds
are gusts greater than 125km/h.
The storm that caused the damage
at Kurnell was being monitored and was
displayed on the graphical warnings. These
graphical warnings show the storm(s) and
the likely areas to be affected and the
potential position of the storms in ten
minute intervals for the next hour.
The storm began to affect the southern
suburbs of Sydney with strong winds and
heav y rain and the suburb of Kurnell bore
the brunt of the storm. In Kurnell the
damage signature, eyewitness reports,
observations from radar and wind readings
from local weather stations confirmed that
a tornado passed over the suburb.
Tornados are rated from F0 to F5 rising
in severity the higher the number. This
tornado was categorised as an F2. An F2
tornado has wind gusts between 181km/h
and 253km/h with average damage path of
around 200 metres. An F5 tornado will have
wind gusts in excess of 400km/h.
The weather station at Kurnell recorded
a wind gust of 213km/h at 10:30. This was
the strongest wind gust ever recorded
in New South Wales and it is likely that
the tornado passed over or very near this
Waterspouts are more common than
tornados but are generally much weaker
than their land based counterparts.
Waterspouts do move from the sea over
A curious but rare phenomenon of
tornados and stronger waterspouts is that
they can suck up large numbers of small
fish and aquatic animals and deposit them
further inland ... yes, raining fish. h
SEVERE THUNDERSTORM WARNINGS
the Kurnell tornado
Warning area issued at 07:51 on the 16th
Above: Graphical warning of the storm the
“ Very Dangerous” tag was included before
the storm reached Kurnell, (Below) radar
image of the storm.
Warning at 08:28 showing the warning area,
identified severe storms with the movement
and the areas of immediate threat.
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