Seasonal Climate Outlook

Recent climate

July rainfall was decile 8 -10 for the SWLD, the wettest July since 1996. This was due to 18 days of continuous rain from cut-off low pressure system and a series of cold fronts, due to negative SAM in the first half of the month. July maximum temperatures were average and minimum temperatures were very much above average, with very little frost reported. Rainfall decile map for 1 April to August shows decile 8-10 rainfall for the majority of the SWLD.

Rainfall decile map for the South West Land Division for 1 April to 31 July 2021.

In July, the atmospheric pressure was very much lower than normal over the SWLD due to a cut-off low pressure system and a series of cold fronts, which brought widespread rain to the SWLD.

Indian Ocean sea surface temperatures north-west of Western Australia are warmer than average, which can favour above average rainfall for parts of Australia. The August to October 2021 SST forecast by the Bureau of Meteorology indicates SSTs are likely to remain warm north of WA as the negative IOD remains.

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. The Southern Annular Mode (SAM) index has recently been positive, but is forecast to return to neutral levels in the coming days, and remain so until the end of August. A neutral SAM has little influence on Australian climate. For more information, see the Bureau of Meteorology’s Climate Driver Update.

The negative Indian Ocean Dipole (IOD) event continues. A negative IOD increases the chances of above average winter–spring rainfall for much of southern and eastern Australia. It also increases the chances of cooler than average days in southern Australia for winter–spring. The last negative IOD was in 2016.

The El Niño–Southern Oscillation (ENSO) is neutral. Three of the seven surveyed models indicate a La Niña will develop in the Pacific Ocean from October.

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