Tropical Cyclones

Tropical cyclones can persist for many days. They may follow quite erratic paths and usually dissipate over land or colder oceans.

How long a tropical cyclone lasts is determined by how favourable the atmospheric environment is; cyclone movement; and sea surface temperatures. While most cyclones undergo a life-cycle of 3-7 days some weak ones only briefly reach gale force while others can be sustained for weeks if they remain in a favourable environment.

Cyclone Rewa formed northwest of the Solomon islands on 28 December 1993 and finally decayed below cyclone strength in the Coral Sea east of Brisbane 24 days later on 21 January 1994. 

The longest lived tropical cylone in the Southern Hemisphere was tropical cyclone Freddy Read More

Tropical cyclones are called hurricanes in the Atlantic and Eastern Pacific, typhoons in Southeast Asia, and cyclones in the Indian Ocean and Western Pacific around Australia.

Tropical Cyclone Yasi track. Image from www.bom.gov.au, CCBY.

The formation of a Tropical Cyclone has a number of stages

1) Initially a low air pressure system (depression) with convection currents starts to gather moisture and clouds begin to develop.

Tropical cyclones begin with continuous cloud build up even during the night time. The sun helps to heat the ocean and produces water vapour that forms clouds.

2) The second phase of Tropical Cyclone formation is linked with a low air pressure system that starts to pull clouds in and rotate.

It's not quite a Tropical Cyclone at this stage but most likely to develop into one.

At the center of a mature Tropical Cyclone, air sinks rather than rises. For a sufficiently strong storm, air may sink over a layer deep enough to suppress cloud formation, thereby creating a clear eye. Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular in shape, and is typically 30–65 km in diameter, though eyes as small as 3 km and as large as 370 km have been observed.

Tropical cyclones out at sea cause large waves, heavy rain and high winds, often disrupting shipping and, at times, causing shipwrecks.

Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent formation of tropical cyclones.

On land, strong winds can damage or destroy vehicles, boats, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles.

The storm surge, or the increase in sea level due to the cyclone, is typically the worst effect from land-falling tropical cyclones, historically resulting in a large proportion of tropical cyclone deaths.