Seasonal Climate Outlook

Summary

The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for July to September 2021 is indicating less than 40% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD). The SSF longer outlook for July to October is similar.

• For July to September 2021, the SSF is indicating less than 40% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD). The most probable rainfall decile map indicates decile 2-3 for the SWLD. Predictive skill based on June conditions is mostly poor to moderate (50-70% consistent).
• The longer lead SSF forecast for July to October 2021 rainfall is indicating less than 40% chance of exceeding median rainfall for the majority of the SWLD. Most likely decile range maps is indicating decile 2-3 for the SWLD. Skill is poor to moderate at 50 to 70% consistent.
• The Bureau of Meteorology’s seasonal outlook for July to September indicated 55-75% chance of exceeding median rainfall for the SWLD. Predictive skill is poor to good (45-75% consistent). The current outlook for August to October is similar with wetter conditions more likely. Skill is poor to moderate (45-65%).
• Temperature outlooks from the Bureau for July to September 2021 indicate a 50-80% chance of above average day-time maxima, higher chances for the South West corner (skill 55-75%), and 70-80% chance of exceeding above average night-time minima for the SWLD (skill 45-55%).
• June rainfall was average in the north, below average in the central grainbelt, and above average along the southern coast and Esperance. June maximum and minimum temperatures were generally average to below average.
• The main climate driver influencing the SWLD is the positive Southern Annular Mode (SAM) that is expected to remain positive until the end of July. A positive SAM could see a decrease in rainfall over South West WA. There is a high probability that a negative Indian Ocean Dipole will develop by August and persist through to October increasing the chance of rainfall in eastern and southern Australia, with cooler days expected in the south.

Three month outlook for the South West Land Division of Western Australia

Statistical Seasonal Forecasting (SSF)

DPIRD’s Statistical Seasonal Forecasting (SSF) system uses historical relationships between global sea surface temperature and sea level pressure with rainfall in the SWLD of 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 July to September 2021, the SSF is indicating less than 40% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD). The most probable rainfall decile map indicates decile 2-3 for the SWLD. Predictive skill based on June conditions is mostly poor to good (50-75% consistent).

SSF forecast of the probability of exceeding median rainfall for July to September 2021 using data up to and including June.

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

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–S). 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 July to September indicated 55-75% chance of exceeding median rainfall for the SWLD. Predictive skill is poor to good (45-75% consistent). The current outlook for August to October is similar, with wetter conditions more likely. Skill is poor to moderate (45-65%).

Temperature outlooks from the Bureau for July to September 2021 indicate a 50-80% chance of above average day-time maxima, and higher chances for the South West corner (skill 55-75%), and 70-80% chance of exceeding above average night-time minima for the SWLD (skill 45-55%).

Rainfall outlook for July to September 2021 for Western Australia from the Bureau of Meteorology, indicating 55-75% chance of above median rainfall for the SWLD.

Percent Consistent skill of the Bureau of Meteorology’s outlook for July to September.

Looking at other rainfall forecasting models, all but one of 12 models are indicating neutral to above median rainfall for the SWLD for July to September 2021.

Model distribution summary of 12 models (not including the SSF) which forecast July to September 2021 rainfall in the South West Land Division.