Tropical cyclones
Tropical cyclones are low pressure systems that form over warm tropical waters and have well defined wind circulations of at least gale force strength (sustained winds of 63 km/h or greater with gusts in excess of 90 km/h).
Technically they are defined as a non-frontal low pressure system of synoptic scale developing over warm waters having organised convection and a maximum mean wind speed of 34 knots or greater extending more than half-way around near the centre and persisting for at least six hours....
The severity of a tropical cyclone is described in terms of categories ranging from 1 to 5 related to the zone of maximum winds.....
Australia continues to feel the effects of one of the strongest La Niña's on record. During La Niña events, tropical cyclone numbers are typically higher than normal during the November to April period, while summer daytime temperatures are often below average, particuarly in areas experiencing excess rainfall.....
Climate indicators of ENSO continue to indicate a strong, mature La Niña, although there are clear signs the event has passed its peak. Pacific Ocean temperatures have increased, especially below the surface, while atmospheric indicators such as the Southern Oscillation Index (SOI), trade winds and cloud patterns have eased from their peaks reached about a month ago......
These observations are consistent with long-range forecast models surveyed by the Bureau which show the Pacific gradually warming during the southern autumn. Given that March to June is the ENSO transition period, there is a spread among the model predictions for the middle of 2011. The most likely outcome is for a return to neutral conditions, but there is a chance of La Niña persisting for the rest of the year.
Climate indicators of ENSO continue to indicate a strong, mature La Niña, although there are clear signs the event has passed its peak. Pacific Ocean temperatures have increased, especially below the surface, while atmospheric indicators such as the Southern Oscillation Index (SOI), trade winds and cloud patterns have eased from their peaks reached about a month ago......
These observations are consistent with long-range forecast models surveyed by the Bureau which show the Pacific gradually warming during the southern autumn. Given that March to June is the ENSO transition period, there is a spread among the model predictions for the middle of 2011. The most likely outcome is for a return to neutral conditions, but there is a chance of La Niña persisting for the rest of the year.
Australian Bureau of Meteorology sea surface temperature mapping on February 3 2011
Exceeding mean temperature probability February-April 2011
TROPICAL CYCLONE IMPACTS ALONG THE AUSTRALIAN EAST COAST FROM NOVEMBER TO APRIL 1858 TO 2000
La Niña - Detailed Australian Analysis
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