Document 387422

What are cyclones?
0 Cyclones are giant, spinning whirlwind storms. In
order for a cyclone to be identified as a cyclone, it
must be travelling over 119 kilometres per hour and it
must have been formed over the ocean in a tropical
region.
0 In North America, they are called hurricanes and are
called typhoons in Asia.
0 Tropical cyclones, in the Southern Hemisphere spin
clockwise, and hurricanes and typhoons in the
Northern Hemisphere spin anti-clockwise. The
average life of a cyclone is one week.
How are cyclones formed?
0 Tropical cyclones are formed over the ocean in the area around
the equator, between the Tropic of Cancer and the Tropic of
Capricorn. In order for a cyclone to form, the ocean waters need
to be warm, at least 26°C.
0 Above the warm ocean, water evaporates and form clouds. If
there is low air pressure where the clouds are formed, it pulls
them in and they begin to rotate. It is the Earth’s rotation and
spinning on its axis that causes the cyclone’s clouds to rotate.
Clouds will continue to form and begin spinning more.
0 This is the stage when it can develop into a mature cyclone, or
lose its momentum. Even if it has developed into a mature
cyclone, it can still grow in size and increase its wind speed.
0 Once a cyclone arrives over land, its strength weakens and it
begins to fade out. This is due to the lack of moisture and heat
compared to the ocean over which it was formed.
How often do they occur?
0 Cyclone season in Australia is between November and
April, but cyclones can still occur in the month of May.
0 The season for hurricanes and typhoons in the
Northern Hemisphere is between June and November.
0 According to the Bureau of Meteorology, Australia has
on average 13 cyclones a year. Half of these occur in
the western regions.
Severity and Categories
Category
1
2
3
4
5
Wind Gusts
126 –
169km/h
Gales
126 –
169km/h
Destructive
170 –
224km/h
Very
Destructive
225 –
279km/h
Very
Destructive
Winds above
280km/h
Very
Destructive
Ocean Swells
Damage
1.2 – 1.6m


slight damage
trees and farmland damaged
1.7 – 2.5m


structural damage
house roofs and most likely power failures
2.6 – 3.7m


structural damage
house roofs and most likely power failures
3.8 – 5.4


significant roofing and structural damage
airborne debris, widespread power failure

almost total destruction and extremely
dangerous
houses flattened, cars over turned
more than
5.5m

The Eye of a Cyclone
0 The eye is in the centre of a cyclone and can vary in
size, from 10 kilometres to 100 kilometres, depending
on the severity of the storm.
0 Due to the least amount of air pressure in the eye, it
produces clear weather with light winds, no clouds,
no rain and some sunshine.
0 After the eye passes, and the other side of the cyclone
hits, the wind blows with equal strength but in the
opposite direction.
Names of Cyclones
0 Each cyclone is named from one of the names in the
below table. The names start from the top of the list
and take it in turns to be a male or female name. Once
the end of the list is reached it begins again.
Australian Region Names
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
PQ
R
S
T
UV
WXY
Z
Anika
Billy
Charlotte
Dominic
Ellie
Freddy
Gabrielle
Hamish*
Ilsa
Jasper
Kirrily
Lauence
Magda
Neville
Olga
Paul
Robyn
Sean
Tasha
Vince
Anthony
Bianca
Carlos
Dianne
Errol
Fina
Gran
Heidi
Iggy
Jasmine
Koji
Lua
Mitchell
Narelle
Oswald
Peta
Rusty
Sandra
Tim
Victoria
Alessia
Bruce
Cathy*
Dylan
Edna
Fletcher
Gillian
Hadi
Ita
Jack
Kate
Lam
Marcia
Nathan
Olwyn
Quang
Raquel
Stan
Tatjana
Uriah
Alfred
Blanche
Caleb
Debbie
Ernie
Frances
Greg
Hilda
Ira
Joyce
Kelvin
Linda
Marcus
Nora
Owen
Penny
Riley
Savannah
Trevor
Veronica
Zelia
Zane
Yvette
Wallace
* Cyclone names marked for replacement.
Ann
Blake
Claudia
Damien
Esther
Ferninand
Gretel
Harold
Imogen
Joshua
Kimi
Lucas
Marian
Noah
Odette
Paddy
Ruby
Seth
Tiffany
Verdun
Areas Prone to Cyclones
0 The most cyclone prone areas include Queensland,
Western Australia and the Northern Territory.
Cyclone Tracy, Dec1974
Northern Territory
0 Tropical cyclone Tracy struck Darwin in the early hours of
Christmas Day, 1974 and was rated a Category 4. Before
the failure of instruments, the wind gauges registered
speeds of 217km per hour. Cyclone Tracy caused massive
and infrastructure damage as well as huge commercial and
industrial losses. Over 80 percent of all buildings were
destroyed or seriously damaged. The cyclone resulted in
the death of 71 people, which included 22 who were lost at
sea. Approximately 35,000 people in a population of
47,000 were evacuated due to the lack of food, shelter,
water, medical aid and the threats of the spread of
diseases.
Cyclone Yasi, Jan 2011
Queensland
0 Cyclone Yasi developed as a tropical low north-west of Fiji
29 January, 2011. On 30 January it was named Yasi by the
Fiji Meteorological Service. On 2 February it was upgraded
a Category 5 system and made landfall near Mission Beach
early on 3 February.
0 Significant wind damage was reported between Innisfail
and Townsville. The towns of Tully and Cardwell suffered
major damage to structures and vegetation. There was one
recorded death. The largest rainfall totals of 200 – 300mm
in 24 hours between Cairns and Ayr, causing some
flooding. A 5 metre tidal surge was observed at Cardwell.