Forecast

Issue Notes

The hemispheric long wave pattern has remained stable in recent weeks. There are six main troughs. Currently the most significant troughs are near the longitudes of the Indian Ocean, Western Australia, New Zealand, the south Pacific, the southeast Pacific, and the Atlantic Ocean.

Summary:

Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 25 September to 29 September, 29 September to 3 October, and 9 October to 13 October. Rain events originating in the tropics and moving south are possible about 2 October to 6 October. Over Western Australia the strongest cold fronts should occur about 25 September to 29 September, 29 September to 3 October, and 10 October to 14 October.

Issue Notes - Issued Sep 10

ENSO status: Neutral IOD status: Positive Sea surface temperatures (SSTs) continued the cooling trend over the central Pacific during August, with areas in the eastern equatorial Pacific exhibiting below average temperatures for the first time in about two years. The Nino3.4 index lingered between 0.2 and 0.1 through the month of August. The Southern Oscillation Index (SOI) recorded a value of -4.4 during the past month, which remains in neutral territory. Current consensus suggests warmer than average SSTs will persist across the equatorial Pacific Ocean through the austral spring, but well within neutral values. Although, three out of eight international models maintain a slightly warmer than average Pacific Ocean through the end of 2019, none of these are likely to reach El Nino thresholds during the 2019/2020 summer. Moreover, 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. All six international models maintain a strong positive event until the beginning of the summer. The climate outlook for spring favours below average rainfall across the southern half, and in particular the eastern half of the continent. During Positive IODs, central and southeastern Australia tend to see a reduction in rainfall during the end of winter and spring due to a reduction of moisture streaming from the northwest. On the other hand, far southern Victoria and western Tasmania could see above average rainfall during this period as a sudden stratospheric warming (SSW) over Antarctica looks to enhance the negative phase of the southern annular mode (SAM) over the coming months.