Summary
Recent conditions: growing season rainfall (since 1 April) has been decile 4-10 for the majority of the South West Land Division (SWLD), after some good falls in June.
Rainfall outlook for SWLD for July to September, all models indicate below median rainfall, based on a survey of twenty national and international models.
Things to consider:
- June rainfall was average to above average except for the northern Central West forecast district. June maximum and minimum temperatures were very much below average due to southerly winds coming from Antarctica.
- Bureau of Meteorology is continuing the El Niño Alert. There is also a high chance of a positive Indian Ocean Dipole developing in July. This would reduce rainfall for the SWLD until November.
- Bureau’s ACCESS-S model indicates that July to September maximum temperatures are four times more likely to be in the highest 20% when compared to the historical range of maximum temperatures. This means there is a high chance of a warmer and drier than normal July to September.
- Southern Annular Mode is forecast to be negative first three weeks of July. In a negative SAM phase, the belt of westerly winds expands and is positioned more northwards towards the equator and Australia. This results in stronger than normal westerly winds, lower atmospheric pressure, more cold fronts and more storm systems over southern Australia.
- The Bureau of Meteorology’s Water and the Land forecast (average of seven models) is indicating between 1-50mm of rain for the SWLD in the next eight days from a cold front.
Rainfall outlook for the south-west of Western Australia
Summary of 20 national and international models show that the majority of models indicate below normal chances of exceeding median rainfall for the SWLD for July to September 2023, and further ahead to spring September to November.
Survey of seven models, also has drier conditions continuing into the end of the year October to December. Remember, however, the further out the model forecasts, the least skill it has.
