Tropical cyclones
General characteristics
a gigantic mass of revolving moist air
has a disc-like shape with a vertical scale of tens of kilometers of cumulonimbus
clouds and a horizontal span of hundreds of kilometers
extremely powerful storm systems
intense low pressure systems
it is like a travelling heat engine
it feeds in a continuous supply of latent heat released from the condensation of
ascending moist air from the ocean waters
Naming
they are known as hurricanes in the US, typhoons in Asia and tropical cyclones in
Australia
When they occur
they develop in late summer and early autumn over the tropical oceans (November -
April) in the southern hemisphere, and from June to November in the norther
hemisphere
they develop over warm oceans where the surface water temperature is higher than
27°C
they develop between 5° and 20° north and south of the equator
Pressure
pressure within the tropical cyclone may be as low as 920hPa (category 5)
Size
diameter of the vortex is about 600km and may reach 800km in a category 5 storm
central eye is about 30-50km in diameter and is surrounded by vortices comprised of
towering cumulonimbus clouds
dry air in the eye usually descends slowly and warms adiabatically; near the surface, it
may be 5-8 degrees warmer than the surrounding cooled air
Wind speed
TCs are characterised by very steep pressure gradients and strong cyclonic (clockwise
in the southern hemisphere) circulation
Cyclones with a max wind speed of less than 60km/h = tropical depressions
when the max speed ranges between 60 and 120km/h = tropical storm
when the max speed exceeds 120km/h = tropical cyclone
, Predictability
tropical cyclones are fairly predictable in speed and direction although their tracks
may be fairly erratic
tropical cyclones move forward at different speeds
Duration
lifespan varies from 3 to 8 days
Damage caused
tropical cyclones are smaller than mid-latitude cyclones but are more violent and
cause more damage
Area Name Season
North Atlantic
Ocean Hurricane June - November
all the year but most
North Pacific
Typhoon frequent and intense
Ocean
June - November
South Pacific
Ocean Tropical cyclone November - April
South Indian
Tropical cyclone November - April
Ocean
General characteristics
a gigantic mass of revolving moist air
has a disc-like shape with a vertical scale of tens of kilometers of cumulonimbus
clouds and a horizontal span of hundreds of kilometers
extremely powerful storm systems
intense low pressure systems
it is like a travelling heat engine
it feeds in a continuous supply of latent heat released from the condensation of
ascending moist air from the ocean waters
Naming
they are known as hurricanes in the US, typhoons in Asia and tropical cyclones in
Australia
When they occur
they develop in late summer and early autumn over the tropical oceans (November -
April) in the southern hemisphere, and from June to November in the norther
hemisphere
they develop over warm oceans where the surface water temperature is higher than
27°C
they develop between 5° and 20° north and south of the equator
Pressure
pressure within the tropical cyclone may be as low as 920hPa (category 5)
Size
diameter of the vortex is about 600km and may reach 800km in a category 5 storm
central eye is about 30-50km in diameter and is surrounded by vortices comprised of
towering cumulonimbus clouds
dry air in the eye usually descends slowly and warms adiabatically; near the surface, it
may be 5-8 degrees warmer than the surrounding cooled air
Wind speed
TCs are characterised by very steep pressure gradients and strong cyclonic (clockwise
in the southern hemisphere) circulation
Cyclones with a max wind speed of less than 60km/h = tropical depressions
when the max speed ranges between 60 and 120km/h = tropical storm
when the max speed exceeds 120km/h = tropical cyclone
, Predictability
tropical cyclones are fairly predictable in speed and direction although their tracks
may be fairly erratic
tropical cyclones move forward at different speeds
Duration
lifespan varies from 3 to 8 days
Damage caused
tropical cyclones are smaller than mid-latitude cyclones but are more violent and
cause more damage
Area Name Season
North Atlantic
Ocean Hurricane June - November
all the year but most
North Pacific
Typhoon frequent and intense
Ocean
June - November
South Pacific
Ocean Tropical cyclone November - April
South Indian
Tropical cyclone November - April
Ocean
