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Wednesday, April 14:
Sydney’s
Superstorm
By Michael Bath*
At SILICON CHIP, we have something of a fascination about lightning.
Perhaps it’s the immense amount of energy involved.
Perhaps it’s because of the damage we’ve seen it cause.
Perhaps it’s because it IS fascinating!
It’s
It's when the lightning is a little close to home, though, that
fascination can turn to fear! This is the story of the “big one” which
didn’t get away – officially Australia’s most costly natural disaster.
O
ur fascination pales into insignificance when compared
to some “storm chasers”: amateurs (mostly) who study storms – and
all their components – with amazing
dedication. Often they’re more up-todate than the official Weather Bureau!
Michael Bath is one such storm
chaser. We’ve seen his work before
in SILICON CHIP. Michael not only
chases storms, he photographs them.
He writes about them. He follows their
progress as closely as he can. He has
even set up a website dedicated to
them (see separate panel).
Which brings us to early in the day
of April 14, 1999. Michael takes up
the story:
In the hours before the storm which
hit Sydney, the email, internet connections and phones of the storm chasers
were buzzing.
The weather bureau issued no warnings – it was as if they missed the event
completely despite being contacted
with very reliable information (as you
will read later).
The day started out with a casual
10 Silicon Chip
comment that “maybe a storm is possible today”. Some altocumulus cloud
about, a moisture haze and a forecast
of a thundery day for Canberra were
the reason for this outlook.
By late morning small cumulus
clouds had developed in a line from
the far southwest towards the coast
south of Sydney. But by early afternoon some were starting to spread out
as altocumulus – not usually a good
sign for thunderstorm development.
One or two of the larger clouds
actually glaciated (meaning they took
on a classic, towering anvil shape) but
with very low tops, probably no more
than 4-5,000 metres but these were
persisting somewhat (something I
had observed a few times in the past,
but I did not make the connection at
the time).
Altocumulus began to dominate
and it became mostly cloudy during
the middle of the afternoon. The only
sign that something may occur later
was more crisp cumulus congestus
(large cumulus cloud masses which
grow higher than they are wide – a
classic sign of a cloud mass developing into a storm) way to the south,
just visible under the altocumulus in
Sydney.
Around 4pm it became apparent
that the congestus to the far south was
certainly looking promising and worth
keeping an eye on.
I suspected that some storms might
get going very close to the coast south
of Sydney and then remain out to sea,
but perhaps a lightning show would
result.
By 5pm I could see that a thunderstorm was gathering strength about
80km SSE. Having a good feel for
locations/distance of storms, I made
a mental note that it appeared to be
over land in the southern Wollongong
area. It would most likely just move
offshore and that would be it.
However, the tower had a very
strong vertical appearance (on the NW
flank that I could see), indicating a
very strong updraft and the potential
for severe weather.
I wanted to check the radar to give
me an indication of any other develop-
matically on its NW flank as the storm
edged over the coast, indicating that it
could clip the coast again to the north
– over Sydney’s southern suburbs.
“The bureau was warned. . .”
The classic anvil-shaped thunderhead towering sometimes thousands of metres
above the surrounding cloud. This is caused by the updraft of moisture-laden
air currents in the cell. When the moisture condenses in the cold higher levels,
the air current cannot support it and it falls as rain. If it freezes, it can fall as
hail, although most of it melts before it reaches the ground.
ment and to determine the direction of
movement of the storm but didn’t get
to see it until after 6.30pm. Lightning
could now be seen about 50km SE at
this stage.
From a website I subscribe to, I
downloaded the latest Sydney radar
images covering the period 5.30pm to
6.30pm local time.
Then I received my email. A message on the aussie-weather mailing list
reported that a severe storm had just
been through the Shellharbour area
(about 100km south of Sydney) and
that golf ball sized hail was reported
to the local radio station.
The storm looked very severe with
lowerings, or parts of the clouds jutting out significantly lower than the
rest or the base of clouds, almost to
the ground.
The system was back-building dra-
The email author said that he had
in fact phoned the Bureau of Meteorology at 6pm to report the storm, only
to be greeted with scepticism. If we
could see what was happening, why
couldn’t the Bureau?
Obviously he was dismissed as
an unreliable spotter as no severe
thunderstorm advice or warning was
issued (although one was belatedly
issued at 10.20pm, long after the storm
had passed).
By 7pm it was obvious on both
radar and visually (my home is about
40km from the coast) that the storm
was moving directly NNE and heading straight into the southern Sydney
suburbs. In fact by 7pm there was
already maximum reflectivity on the
radar and the storm was over the Royal
National Park on Sydney’s southern
outskirts, heading towards Botany Bay
and Sydney Airport.
Lightning was frequent to the
south-east but it seemed that a dead
cell or other cloud was to the west of
the storm, blocking the view of any
lightning bolts.
I could however see the glowing
outline of the storm tops and reflections around the rest of the sky.
Visually it continued like this until
Left: thermal image of the storm taken by the NOAA12
satellite at 7.13UCT (9.13pm Sydney time); courtesy of
CSIRO. Above is the radar image taken at around the same
time with the storm sited directly over Sydney’s eastern
suburbs, which copped the brunt of the damage; courtesy
Bureau of Meterology.
JULY 1999 11
Everyone has a story...
by James Crouch, Rushcutters Bay.
It was about 7:35pm. I had about
two minutes warning – I could hear
a distant roar but didn’t know what
it was at first. It just got louder and
louder.
Things started breaking as soon
as the first isolated hail stones began
falling: neighbour’s windows, roof
tiles, that sort of thing.
The roar was quite loud but still
distant. For a moment it sounded
like “things” were falling out of the
sky and I actually feared for a few
seconds that it was debris, not ice!!
The tiles on my roof were taking a
pounding, ceiling plaster was flaking
off all over (I guess a combination of
hail and tile impacts).
There was nothing I could do and
I didn’t have a view, so I went down
to the street and sat under shelter
with a few neighbours and watched
as 70mm hailstones slammed into
the footpath.
I couldn’t see much in the way of
cloud but there was lightning every
2-3 seconds.
Bayswater Rd, empty of traffic,
was covered in a 50mm layer of ice
(ice was still piled up in corners 3
hours later).
The heaviest hail lasted about
10-15 minutes and then it rained
(showered, whatever) until 2am-ish.
That was the killer.
I drilled a few holes in my ceiling
where it was sagging the worst (and
until I ran out of pots and pans) and
then checked my neighbours.
I wasn’t the worst; the girl across
the landing had a 2-3 litre per minute
flow from the light in her kitchen for
a while, and sundry other leaks of
various flow rates.
I climbed up into the ceiling: there
were at least 300 tiles shattered or
cracked; you could see the sky all
over the place.
Once they’d isolated her power
and we’d drilled holes in other peoples ceilings, I went and checked
my car. It was a Daihatsu Feroza.
The bonnet was trashed – 20-odd
4-5cm dents and one of the rear side
windows was smashed – with a bit
of resultant water damage.
Not so bad. . . I haven’t got onto
the insurance company yet so I have
no idea when it’ll have a chance to
get fixed up. Meantime I guess that
I’m up for driving on storm chases!
I had a pleasant night’s sleep on
cushions in the hallway – that was
the only place that didn’t have leaks!!
just as in Sydney. It can also make the
storm rotate and is the phenomenen
which also breeds tornados.
In most thunderstorms, the updrafts
of air reach a point where the water
and ice they contain cannot be supported and they collapse, dumping
their rain and sometimes ice (as hail)
in the process.
A second storm
Towards 9pm, fresh southeast
winds spread in with a layer of strato-cumulus, blocking the storm as it
edged out over the northern beaches.
At about the same time the first reports of giant hail began to filter in
and the discussions on the ’net got
quite excited.
Also at this time, another storm with
hail passed through the eastern suburbs on a similar track to the supercell.
Later (between 10pm and 11pm)
a storm with some intense cloud-toground strokes spread through the
western suburbs dumping some heavy
rain but no hail. Brief blackouts occurred including at my place at 11pm.
It wasn’t until the next day that the
analysis of the day’s observations and
the radar clearly showed the significance of the event.
The radar patterns were classic
supercell from about 6.30pm onwards
with a clearly defined V-notch most of
the time. The V-notch is a particular
shape of the radar image on the screen,
well known to meteorologists as an
indication of a very severe storm.
Almost a tornado
8pm though was now much closer
and bigger.
Radar showed the most intense part
of the storm was right over the eastern suburbs and city and would have
been smashing these areas with hail
officially measured to 9cm diameter,
with larger stones probable.
Just after 8pm the storm became
much more spectacular from my
vantage point to its west – continuous
cloud to cloud lightning, cloud to air,
and cloud to ground, though I could
only see the top half of these.
It coincided with a rapid propagation and development to the NW of
the main thunderstorm, making the
whole structure visible with each
lightning flash.
Is it a supercell?
With a boiling rear flank, a rock
12 Silicon Chip
solid backshearing anvil punching
well through the tropopause and the
continuous lightning, I soon came to
realise this was no ordinary storm. In
fact, it looked to me like the western
flank of a supercell thunderstorm.
In fact, after spending some time
taking lightning photographs I made
the remark that I thought it was a supercell and wondered what damage
had occured or was currently occurring in the most densely populated
parts of Sydney.
A supercell thunderstorm is fairly
rare – perhaps one a year or so in the
Greater Sydney area – and occurs
when the updrafts and downdrafts of
air currents within the storm occur at
the same time due to windshear. This
makes the storm self-sustaining.
A supercell is much more likely to
do a lot of damage over a wide area –
It was disturbing to see a most prominent hook echo on the radar screen
when the storm was right over the
eastern suburbs, though no damaging
winds were experienced there.
A hook echo on the screen can indicate precipitation actually wrapping
around a meso-cyclone. Imagine if a
large tornado had touched down as
well!
The storm tracked to the NNE and
was well defined for almost four
hours. Contrary to some early reports,
there was no cell splitting or another
storm suddenly developing closer to
Sydney – the one storm cell just propagated on its NW flank continuously.
The early afternoon observation of
persisting low topped glaciated cells
has preceded supercell development
on other occasions.
As at 11th May, the total insured
damages bill is in excess of $A1.4
billion, now making it the most costly
natural disaster in Australian history,
surpassing the Newcastle earthquake
(1989) and Tropical Cyclone Tracy in
Darwin (1974).
Although the time of year and the
area affected by the storm is unusual
for a supercell, many hailstorms with
similar-sized hail (but officially recorded hail sizes slightly smaller than
this event) have occurred in Sydney,
even in recent years.
Most notable were the supercell
hailstorm of Sunday 18th March 1990
affecting the western suburbs and the
supercell of Monday 21st January
1991 affecting the northern suburbs.
However, insured loses for these
two events are far lower than for the
April 1999 event.
Just after 8pm
the storm
became much
more
spectacular
from my
vantage point
to its west –
continuous
cloud to cloud,
cloud to air,
and cloud to
ground lightning, though I
could only see
the top half of
the latter.
* Michael Bath is the editor of the severe
weather newsletter, “Storm News” and has a
huge library of storm and lightning photo-graphy. He also conducts a website dedicated
to the subject of severe weather at www.
australiansevereweather.simplenet.com
On this site there are links to many other
sites on similar subjects.
Radar Image courtesy Bureau of Meterology.
Satellite image courtesy CSIRO.
Tracking the Storm by Tracking the Lightning
Regular S ILICON C HIP readers
would be aware of the LPATS Lightning Positioning and Tracking System (see the article in the November
1996 issue).
As you might expect, Kattron's
Ken Ticehurst had been monitoring
the storm earlier in the day, just as
had Michael Bath.
“We could see the storm's path
bearing down on Sydney and were
amazed that the weather bureau
didn’t issue any warnings,” said Ken.
“In the overall scheme of things,
though, this thunderstorm didn’t
look all that big because most of the
lightning was CC strokes”.
LPATS works by detecting the
electromagnetic radiation of a cloudto-ground (CG) lightning stroke
between 2 and 450kHz.
Some cloud-to-cloud (CC) strokes
are also detected but as their radiation is mainly in the VHF range, the
detection range is much less.
In most thunderstorms, CCs are
usually 90% of the lightning activity. In this storm, with all the hail, it
may well have been higher. Certainly
from the SILICON CHIP offices (close
to the coast in northern Sydney) the
impression was overwhelmingly CC,
even with the numerous CG strokes
witnessed (actually CW or cloud-towater because most of the activity
was by this time off shore).
The lightning display, by the way,
was rated by SILICON CHIP staff as
easily the most spectacular they had
ever seen).
But in terms of CG activity this
storm was not all that ferocious –
with around 600 strokes per hour at
its peak (11.30pm).
At 8.30pm, about the peak of damage in the Eastern Suburbs, it was
recording 120 strokes per hour.
We have seen thousands of CG
strokes per hour (over a greater area)
in other storms. (The November 1996
article shows a graph of lightning
strokes in Central NSW during November 1995 peaking at more than
3800 mainly C-G strokes per hour!)
The map above shows one of the
lightning stroke “maps” plotted by
Kattron during the storm.
The colour bars on the images
represent % of strokes in 10 minute
intervals from the time shown (top
left of each image), starting with
gray.
Each screen in the full series
represents 1 hour.
SC
JULY 1999 13
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