12-Month Rainfall Forecast

Issue Notes

ENSO status: Neutral, however two models suggest La Niña thresholds may be met again from September. IOD status: Neutral, although it was negative for six weeks between mid-May and late-June SAM status: Negative. The El Niño–Southern Oscillation (ENSO) is currently neutral. However, there are growing signs that La Niña could redevelop in the Pacific Ocean later this year, prompting the US Climate Prediction Centre to issue a La Niña Watch this week. Two models forecast temperatures reaching the La Niña threshold during September. The Indian Ocean Dipole (IOD) is currently neutral, although we saw six consecutive weeks below the negative IOD threshold between mid-May and late-June. The IOD index needs to stay below -0.4C for eight consecutive weeks to be officially declared as a negative IOD event. The IOD ducked back into neutral territory thanks to recent warming in the western Indian Ocean. While a negative IOD has not been officially declared, the negative weekly values may enhance rainfallacross central and southern Australia. Three of the five models are forecasting the negative IOD to develop in winter, with another one indicating development in early spring. Most of the models suggest that the negative IOD will continue through until mid spring. During winter, much of the Australia is likely to be wetter than normal, apart from far southern WA and SA, southern VIC and southwestern TAS. The weekly negative IOD values may be influencing this outlook, potentially feeding moisture into cold fronts sweeping across central and southern Australia. Therefore a normal to above normal snow season is forecast. Springs rainfall at this stage is forecast to be above normal for much of the Australia, apart from southwestern TAS and WA. Again, the negative IOD values may be playing a role in this outlook.