Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for October to December 2022, is indicating mostly neutral (40-60%) probability of above median rainfall for the majority of the South West Land Division (SWLD). 

• For October to December 2022, the SSF forecast is indicating mostly neutral (40-60%) probability of above median rainfall for the majority of the South West Land Division. Greater than 60% probability for part of the Central West and Central Wheatbelt forecast districts.  With less than 40% probability for parts of the South East Coastal forecast district. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Great Southern, South West and South Coastal forecast districts. Decile 2-3 for parts of the Central Wheatbelt, Great Southern, South West and South East Coastal forecast districts, and decile 4-7 elsewhere. Skill is poor to moderate at 50 to 70 % consistent.
• The Bureau of Meteorology’s seasonal outlook for October to December 2022 is indicating 25-65% chance of exceeding median rainfall for the SWLD.  The higher chances are for parts of the Great Southern, South Coastal and South East Coastal forecast districts. Predictive skill is poor to moderate (45-65% consistent). The current longer-term outlook (at time of writing) for November 2022 to January 2023 is neutral (40-60%) chance of exceeding median rainfall with mostly moderate skill (50-75%).
• Temperature outlooks for October to December 2022, from the Bureau indicate a 20-80% chance of above average day-time maxima, with the lower chances for Great Southern, South Coastal and South East Coastal forecast districts. Skill is good at 75-100%. For night-time minima for the SWLD, the Bureau is indicating 40- 80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is good at 75-100%.
• September rainfall was above average for the Central West and Central Wheatbelt forecast districts, below average for South West and South Coastal forecast districts and average elsewhere. September maximum temperatures were average to above average, with below average in land, and minimum temperatures were average to above average. Minimal reports of frost damage.
• The main climate driver influencing South West Land Division climate is the high Mean Sea Level Pressure which is predicted to remain high throughout spring. The Indian Ocean Dipole (IOD) is currently negative and likely to remain through to November. Past negative IOD events generally increase rainfall in the eastern grainbelt. The La Niña in the Pacific, and the positive Southern Annular Mode have little influence on SWLD summer rainfall.

Three Month Outlook for the south-west of Western Australia

Statistical Seasonal Forecasting (SSF)

DPIRD’s Statistical Seasonal Forecast (SSF) system uses historical relationships between global sea surface temperature and sea level pressure with rainfall in south-west Australia to produce forecasts of rainfall for the coming months. Users can click on any station indicated on the map for location-specific forecast information from DPIRD’s Seasonal Climate Information pages. 

For October to December 2022,  the SSF forecast is indicating mostly neutral (40-60%) probability of above median rainfall for the majority of the South West Land Division. Greater than 60% probability for part of the Central West and Central Wheatbelt forecast districts. With less than 40% probability for parts of the South East Coastal forecast district. The most likely decile range map is indicating decile 8-9 for parts of the Central West, Central Wheatbelt, Great Southern, South West and South Coastal forecast districts. Decile 2-3 for parts of the Central Wheatbelt, Great Southern, South West and South East Coastal forecast districts, and decile 4-7 elsewhere. Skill is poor to moderate at 50 to 70 % consistent.

SSF forecast of the probability of exceeding median rainfall for October to December 2022 using data up to and including September.

Percent consistent skill of the SSF at forecasting October to December rainfall using data up to and including September.

Bureau of Meteorology seasonal climate outlook

The Bureau of Meteorology's climate forecast system for monthly and seasonal climate outlooks is the Australian Community Climate Earth-System Simulator – Seasonal (ACCESS–S2). It is a dynamical (physics-based) forecast modelling system and is a collaboration between the Bureau of Meteorology and the UK Meteorological Office.

The Bureau of Meteorology’s seasonal outlook for October to December 2022, is indicating 25-65% chance of exceeding median rainfall for the SWLD.  The higher chances are for parts of the Great Southern, South Coastal and South East Coastal forecast districts. Predictive skill is poor to moderate (45-65% consistent). The current longer-term outlook (at time of writing) for November 2022 to January 2023 is neutral (40-60%) chance of exceeding median rainfall with mostly moderate skill (50-75%).

Temperature outlooks for October to December 2022, from the Bureau indicate a 20-80% chance of above average day-time maxima, with the lower chances for Great Southern, South Coastal and South East Coastal forecast districts. Skill is good at 75-100%. For night-time minima for the SWLD, the Bureau is indicating 40- 80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is good at 75-100%.

Rainfall outlook for October to December 2022 for Western Australia from the Bureau of Meteorology.

Percent Consistent skill of the Bureau of Meteorology’s outlook for October to December

Looking at other rainfall forecasting models, the majority of models are indicating neutral-above chance of exceeding median rainfall for the SWLD for October to December 2022.

Model distribution summary of 12 models outlook for October to December 2022 rainfall in the South West Land Division.

Recent climate

September rainfall was above average for the Central West and Central Wheatbelt forecast districts, below average for South West and South Coastal forecast districts and average elsewhere. September maximum temperatures were average to above average, with below average in land, and minimum temperatures were average to above average. Minimal reports of frost damage.  Rainfall decile map for 1 April to 2 October 2022 shows decile 8-10 rainfall for the majority of the SWLD.

Rainfall decile map for South West Land Division 1 April – 2 October 2022

In September the atmospheric pressure was higher than normal over the SWLD.

Sea surface temperatures have remained warmer than average around much of the Australian coastline, particularly to the north and west. The sea surface temperature outlook for October to December by the Bureau of Meteorology indicates SSTs are likely to remain warmer than normal around Western Australia and the north and south-east of Australia.

The negative Indian Ocean Dipole (IOD) event continues. Models indicate that the negative IOD is likely to persist at least until late spring. A negative IOD typically increases the chance of above average spring rainfall for most of the eastern two thirds of Australia. Past negative IOD events generally increase rainfall in the eastern grainbelt.

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 likely to remain generally positive throughout spring into early summer. During the spring months, positive SAM increases the chance of above average rainfall for parts of eastern New South Wales, eastern Victoria, and south-eastern Queensland, but has a drying influence for western Tasmania. SAM has no influence on rainfall in the SLWD in summer. A positive SAM has a drying influence for parts of south-west and south-east Australia at this time of year.  For more information see the Bureau of Meteorology’s Climate Driver Update.

A La Niña is underway in the tropical Pacific. La Niña increases the chance of above average rainfall for northern and eastern Australia during spring and summer, with little influence over the climate of the SWLD. Models indicate the La Niña may peak during spring and return to neutral conditions early in 2023.

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