Forecast

Issue Notes

The hemispheric long wave pattern has been relatively fast moving in recent weeks. There are five main troughs. Currently the most significant troughs are near the longitudes of South Africa, Western Australia, New Zealand, the south Pacific, and the southeast Pacific.

Summary:

Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 31 August to 4 September, 13 September to 17 September, and 17 September to 21 September. Rain events originating in the tropics and moving south are possible about 15 August to 19 August. Over Western Australia the strongest cold fronts should occur about 31 August to 4 September, 4 September to 8 September, and 16 September to 20 September.

Issue Notes - Issued Aug 8

ENSO status: Neutral IOD status: Positive Sea surface temperatures (SST's) continued a cooling trend over the central Pacific during July. The Nino3.4 index lingered at about 0.5 through the month of July. The Southern Oscillation Index (SOI) recorded a value of -5.6 in July, which is now in neutral territory. Current consensus suggests warmer than average SSTs will remain across the equatorial Pacific Ocean through the austral spring, but well within neutral values. Although, six out of eight international models maintain a warmer than average Pacific Ocean through the remainder of 2019, none of these are reaching El Nino thresholds during the 2019/2020 summer. Moreover, the IRI ENSO forecast suggests less than 50% of another El Nino developing over the next 12 months. On the other hand, the Indian Ocean Dipole (IOD) remains strongly positive. Six out of six international models maintain a positive event until mid-spring. The climate outlook for the four weeks left in winter and spring, favours average-to-below average rainfall across the southern half of Australia, in particular over 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 the first half of spring due to a reduction of moisture streaming from the northwest. SST's along the eastern seaboard remain significantly warmer than average (especially off NSW) maintaining a high risk of extreme weather events such as East Coast Lows (ECLs). These can bring intense periods of rainfall east of the Great Dividing Range, leading to flash flooding.