Summary
The Department of Primary Industries and Regional Development’s (DPIRD) Statistical Seasonal Forecast (SSF) outlook for August to October 2021 is indicating more than 60% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD).
- For August to October 2021, the SSF is indicating more than 60% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD).There is a lower chance of exceeding median rainfall, less than 40%, for Jerramungup and Ravensthorpe shires. The most probable rainfall decile map indicates decile 8-10 for the majority of SWLD. Predictive skill based on July conditions is mostly poor to good (50-75% consistent).
- The Bureau of Meteorology’s seasonal outlook for August to October indicated 35-50% chance of exceeding median rainfall for the SWLD. Predictive skill is poor to good (45-75% consistent). The current outlook for spring, September to November is 35-65%, with higher chances for the South East Coastal forecast district. Predictive skill is moderate to good (55-75%).
- Temperature outlooks for August to October 2021 from the Bureau indicate a 40-50% chance of above average day-time maxima (skill is moderate to good at 55-75%), and 35-50% chance of exceeding above average night-time minima for the SWLD (skill is poor to moderate 45-65%).
- July rainfall was decile 8 -10 for the SWLD; the wettest July since 1996. This was due to 18 days of continuous rain from a 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.
- The main climate driver influencing the SWLD is the neutral Southern Annular Mode (SAM), warmer waters in the Indian Ocean and the negative Indian Ocean Dipole, which increases the chance of rainfall in eastern and southern Australia, with the possibility of cooler days and nights expected in the south.
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 August to October 2021, the SSF is indicating more than 60% chance of exceeding median rainfall for the majority of the South West Land Division (SWLD). There are lower chances, less than 40%, of exceeding median rainfall for Jerramungup and Ravensthorpe shires. The most probable rainfall decile map indicates decile 8-10 for the majority of SWLD. Predictive skill based on July conditions is mostly poor to good (50-75% consistent).
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 August to October indicated 35-50% chance of exceeding median rainfall for the SWLD. Predictive skill is poor to good (45-75% consistent). The current outlook for spring, September to November, is 35-65%, with higher chances for the South East Coastal forecast district, with wetter conditions more likely. Skill is moderate to good (55-75%).
Temperature outlooks for August to October 2021 from the Bureau indicate a 40-50% chance of above average day-time maxima (skill is moderate to good at 55-75%), and 35-50% chance of exceeding above average night-time minima for the SWLD (skill is poor to moderate 45-65%).
Looking at other rainfall forecasting models, the majority are indicating neutral chances of exceeding medain rainfall for the SWLD for August to October 2021.
