Forecast

Issue Notes

The hemispheric long wave pattern has remained stable in recent weeks. There are five main troughs. Currently the most significant troughs are near the longitudes of the southwest Indian Ocean, eastern Australia, the south Pacific, South America, and the Atlantic Ocean.

Summary:

Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 15 December to 19 December, 22 December to 26 December, and 4 January to 8 January. Rain events originating in the tropics and moving south are possible about 12 December to 16 December. Over Western Australia the strongest cold fronts should occur about 18 December to 22 December, 22 December to 26 December, and 4 January to 8 January.

Issue Notes - Issued Nov 8

ENSO status: Neutral IOD status: Positive Sea surface temperatures (SSTs) across the equatorial central Pacific warmed up slightly over the past few weeks. As a reflection, the Nino3.4 index lingered between 0.5 and 0.7 throughout the month of October. The Southern Oscillation Index (SOI) recorded a value of -5.6 during the past month. The current outlook consensus suggests warmer than average SSTs will persist across the equatorial Pacific Ocean through the coming months, but remaining within neutral values. Five out of eight international models maintain a warmer than average Pacific Ocean through the end of 2019 and first quarter of 2020, however, none of these reaching El Nino thresholds. The IRI ENSO forecast continues to suggest 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 October 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. Thus far, Darwin and South Eastern Qld have seen the onset of the wet season this year though a week later than usual. Further south, a negative trend in the Southern Annular Mode (SAM) will continue to enhance frontal activity over the far south during October and early. This is likely to offset the Positive IOD in far southern Victoria and western Tasmania, which could see average-to-above average rainfall during October and early December. Looking further ahead, with no significant signature from ENSO, there are no significant climate drivers tilting the balance towards a drier or wetter summer. The current outlook suggest neutral odds.