Seasonal Climate Outlook

Recent climate

September rainfall was below average in the Central West and parts of the Central wheatbelt and Esperance shire, above average in the south west and average elsewhere. September maximum temperatures were very much above average. September minimum temperatures were above average. Rainfall from 1 April to date has generally beendecile 2-3 in the SWLD.

Rainfall decile map 1 April to 5 October for the South West Land Division, indicating mostly below average rainfall.
Rainfall decile map 1 April to 5 October 2020 for the South West Land Division.

In September, the atmospheric pressure was near normal over the SWLD.

Sea surface temperatures of the Indian Ocean north of Western Australia are warmer than average. The September to November 2020, SST forecast by the Bureau of Meteorology indicates SSTs are likely to remain warm, 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. The Southern Annular Mode (SAM) is expected to be neutral or weakly positive for the first three weeks of October  . For more information see the Bureau of Meteorology’s  Climate Driver Update.

Large parts of the central and eastern Indian Ocean are warmer than average, with surface temperatures close to average in much of the west of the basin. The latest weekly value of the Indian Ocean Dipole (IOD) index to 4 October was -0.06, returning to neutral dipole values. Five of the six surveyed climate models indicate values indicate the IOD will be negative in October, and three continue the event into November. To be considered an official negative IOD event we will need to see values of the IOD index remain at or cooler than −0.4 °C for eight weeks. A negative IOD typically brings above average spring rainfall to most of the eastern two thirds of Australia and to south-east Western Australia.

A La Niña has established in the Pacific Ocean. All models are indicating this to last until January 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 Climate Driver Update 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 Mixed Below average to average
SWLD Mean Temperature Very much above average Very much above average
SWLD atmospheric pressure Near Normal Higher
Indian Ocean Sea surface temperature Warmer Warmer
El Niño/Southern Oscillation (ENSO) La Niña Neutral
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Negative Negative