Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for autumn, March to May 2023, is indicating greater than 60% probability of above median rainfall for the majority of the South West Land Division, although skill is very low this time of the year. 

• For autumn, March to May 2023, the SSF forecast is indicating greater than 60% probability of above median rainfall for the majority of the South West Land Division. Less than 40% probability for parts of the Central West, Lower West, and South West forecast districts, neutral probability for elsewhere. The most likely decile range map is indicating decile 8-10 for the majority of the South West Land Division, decile 2-3 for parts of the Central West, Lower West, and South West forecast districts and decile 4-7 elsewhere.  Skill is mostly poor at 50 to 70 % consistent.  
• The Bureau of Meteorology’s seasonal outlook for autumn, March to May 2023, is indicating 25-40% chance of exceeding median rainfall for the SWLD, with mostly poor skill (45-65%).  The current longer-term outlook (at time of writing) for April to June 2023 is 25-45% chance of exceeding median rainfall with mostly poor skill (45-75%). 
• Temperature outlooks for autumn, March to May 2023, from the Bureau indicate a 80% chance of above average day-time maxima. Skill is moderate to good 65-100%. For night-time minima for the SWLD, the Bureau is indicating 70-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is mostly poor at 45-65%.
• February rainfall was below average. February maximum temperatures were average to above average. Minimum temperatures were average.
• There is a possibility of an El Niño and a positive Indian Ocean Dipole (IOD) developing later this year. If an El Niño coincides with a positive IOD, there is a clear signal for reduced winter-spring rainfall for large parts of the South West Land Division. However skill at this time of the year is low and ENSO outlooks that extend past autumn should be viewed with caution.

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 autumn, March to May 2023, the SSF forecast is indicating greater than 60% probability of above median rainfall for the majority of the South West Land Division. Less than 40% probability for parts of the Central West, Lower West, and South West forecast districts, neutral probability for elsewhere. The most likely decile range map is indicating decile 8-10 for the majority of the South West Land Division, decile 2-3 for parts of the Central West, Lower West, and South West forecast districts and decile 4-7 elsewhere.  Skill is mostly poor at 50 to 70 % consistent.  

SSF forecast of the probability of exceeding median rainfall for autumn, March to May, using data up to and including February.

Percent consistent skill of the SSF at forecasting autumn, March to May rainfall using data up to and including February.

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 United Kingdom Meteorological Office.

The Bureau of Meteorology’s seasonal outlook for autumn, March to May 2023, is indicating 25-40% chance of exceeding median rainfall for the SWLD, with mostly poor skill (45-65%).  The current longer-term outlook (at time of writing) for April to June 2023 is 25-45% chance of exceeding median rainfall with mostly poor skill (45-75%). Temperature outlooks for autumn, March to May 2023, from the Bureau indicate an 80% chance of above average day-time maxima. Skill is moderate to good 65-100%. For night-time minima for the SWLD, the Bureau is indicating 70-80% chance of exceeding above average temperatures, with the higher chances along the coast. Skill is mostly poor at 45-65%.

Rainfall outlook for March to May 2023 for Western Australia from the Bureau of Meteorology

Percent Consistent skill of the Bureau of Meteorology’s outlook for March to May.

Looking at other rainfall forecasting models, the majority of models are indicating low chances of exceeding median rainfall for the SWLD for autumn, March to May 2023.

Model distribution summary of 12 models outlook for autumn, March to May 2023, rainfall in the South West Land Division.

Recent climate

February rainfall was below average. February maximum temperatures were average to above average. Minimum temperatures were average. Rainfall since the start of the year has been below average for the majority of the SWLD.

Rainfall decile map 1 January to 6 March 2023 for the South West Land Division

In February the atmospheric pressure was below normal over the SWLD.

Sea surface temperatures in February are near normal around Australia. The sea surface temperature outlook for March to May by the Bureau of Meteorology indicates SSTs will be normal to warm around Western Australia. Warmer temperatures marginally increase the likelihood of tropical cyclones developing.

The Indian Ocean Dipole (IOD) is neutral and has little influence on Australian climate while the monsoon trough is in the southern hemisphere (typically December to April). Two models (including the Bureau of Meteorology) are indicating the development of a positive IOD in May. While some models suggest positive IOD values may emerge during winter, IOD forecasts made at this time of the year have low accuracy when forecasting through the autumn.

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 currently neutral and is forecast to remain neutral until the end of March. For more information see the Bureau of Meteorology’s Climate Driver Update.

The La Niña continues in the tropical Pacific. However, oceanic indicators of ENSO have returned to neutral values, with atmospheric indicators now also weakening. While models suggest there is an increased in risk of El Niño developing in June, model accuracy when forecasting through autumn is low, and ENSO outlooks that extend past autumn should be viewed with caution.

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.