Seasonal Climate Outlook

Recent climate

October rainfall was below average in the SWLD. October maximum and minimum temperatures, were very much above average.  Growing season rainfall (April to October) was generally below average in the SWLD.

Rainfall deciles for 1 April to 31 October 2020 in the South West Land Division. Indicating below average rainfall for the majority of the SWLD.
Rainfall deciles for 1 April to 31 October 2020 in the South West Land Division.

In October, the atmospheric pressure was slightly higher than normal over the SWLD.

Sea surface temperatures of the Indian Ocean north of Western Australia are warmer than average, this may be favourable for enhancing rainfall over the continent. The November 2020 to January 2021, SST forecast by the Bureau of Meteorology indicates SSTs are likely to remain warm to the north of WA.

The Southern Annular Mode (SAM), also known as the Antarctic Oscillation (AAO), describes the north–south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the southern hemisphere. SAM is currently positive and is expected to remain positive over the 2020-21 summer. La Niña tends to favour positive SAM during the spring to summer months, which typically enhances the wet signal of La Niña in parts of eastern Australia. A positive SAM in summer has little effect on rainfall for WA, but increases temperatures as westerly winds are further south than normal, reducing the sea breeze along the WA coast. For more information see the Bureau of Meteorology’s  Climate Driver Update.

The Indian Ocean Dipole (IOD) is neutral after tending towards positive values in recent months. With the Australian monsoon commencing, the IOD is likely to remain neutral through summer.

La Niña continues in the tropical Pacific. Australian and international climate models suggest it is likely to continue at least into February 2021.  A La Niña is often associated with increased chance of widespread rains and flooding over eastern, central and northern Australia, more tropical cyclones than average and prolonged very warm periods in the south. In a La Niña, there is an increased chance of above average number of tropical systems (cyclones and lows) across northern Australia. The first Australian landfall typically occurs in early December, which is about 3 weeks earlier than usual. For further information, see the Bureau of Meteorology’s Australian Tropical Cyclone Outlook  and  the Northern Rainfall Onset.

The table below gives a summary of past month and three-month South West Land Division (SWLD) climate conditions, and can indicate what is likely to occur in the near future if climate conditions follow the current pattern.

Climate Indicator Past month Past 3 months
SWLD Rainfall Below average Below average to average
SWLD Mean Temperature Very much above average Above average
SWLD atmospheric pressure Higher Higher
Indian Ocean Sea surface temperature Warmer Warmer
El Niño/Southern Oscillation (ENSO) La Niña La Niña
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Positive Negative