Emergency Dispatch Vol 4 2014

18
Cyclone
Hazards & Disasters
Tropical cyclones are low pressure systems in
the tropics that, in the southern hemisphere, have
well-defined clockwise wind circulations with
a region surrounding the centre with gale force
winds.
The gale force winds can extend hundreds
of kilometres from the cyclone centre. If the
sustained winds around the centre reach 119
kilometres per hour, the system is called a
severe tropical cyclone. These are referred to
as hurricanes in North America and typhoons in
Asia.
Cyclone Season and Effects
The tropical cyclone season in Australia
extends from November to April. Cyclones
generally affect coastal areas north of
Perth along the Western Australia and Northern
Territory coasts, most of the Queensland coast
and occasionally the far northern New South
Wales coast. The greatest threat lies north of the
Tropic of Capricorn.
FREQUENCY.
Cyclones occur frequently in the southern
hemisphere, with an average of 10 per year
being tracked by the Bureau of Meteorology in
the Australian region. Cyclones in the Indian and
Pacific Oceans are also closely monitored in
case they threaten Australian islands or nearby
countries.
SEVERITY CATEGORIES.
The severity of tropical cyclones is described in
terms of categories between 1 and 5 related to
the zone of maximum winds. These range from
Category 1 (strongest wind gusts less than 125
km/h), through Category 2 (125–169 km/h),
Category 3 (170–224 km/h), Category 4 (225–
279 km/h), to Category 5 for the most severe
cyclones (wind gusts more than 280 km/h).
EFFECTS.
Cyclones approach from the sea and bring
torrential rains, extreme winds and sometimes
storm surges. Damage varies widely depending
on the path, but can include buildings, crops and
boats at sea. Most deaths from cyclones occur
as a result of drowning (both at sea and during
floods), collapsed buildings, or debris which
becomes lethal projectiles carried by the extreme
winds.