Forecast

Issue Notes

The hemispheric long wave pattern has been relatively fast moving in recent weeks. There are four main troughs. Currently the most significant troughs are near the longitudes of South Africa, Western Australia, eastern Australia, and South America.

Summary:

Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 28 October to 1 November, 3 November to 7 November, and 17 November to 21 November. Rain events originating in the tropics and moving south are possible about 19 October to 23 October. Over Western Australia the strongest cold fronts should occur about 28 October to 1 November, 3 November to 7 November, and 16 November to 20 November.

Issue Notes - Issued Oct 7

ENSO status: Neutral IOD status: Positive Sea surface temperatures (SSTs) across the equatorial central Pacific remain within neutral values. The Nino3.4 index lingered between -0.2 and 0.2 through the month of September. The Southern Oscillation Index (SOI) recorded a value of -12.4 during the past month. The current outlook consensus suggests warmer than average SSTs will persist across the equatorial Pacific Ocean through the austral spring, but well within neutral values. Five out of eight international models maintain a slightly warmer than average Pacific Ocean through the end of 2019, none of these reaching El Nino thresholds during the 2019/2020 summer. The IRI ENSO forecast suggests less than 40% of another El Nino developing over the next 12 months, with a neutral ENSO the most likely outcome. To the west of Australia, the Indian Ocean Dipole (IOD) remains strongly positive, with the highest positive value since the early 2000s. All six international models maintain a strong positive event until December. In terms of rainfall, there is little variation to the outlook issued last month. The climate outlook for spring continues to favour below average rainfall for most of Australia, in particular the eastern half of the continent. During Positive IODs, central and southeastern Australia tend to see a reduction in rainfall during spring, due to a reduction of moisture streaming from the northwest. For northern Australia, the current outlook is for a late onset of the wet season across the Northern Territory and Queensland. A negative trend in the Southern Annular Mode (SAM) on the other hand, is likely to enhance frontal activity over the far south during spring. This is likely to offset the Positive IOD in far southern Victoria and western Tasmania, which could see average-to-above average rainfall during the remainder of spring.