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 South Africa, Western Australia, New Zealand, the southeast Pacific, and South America.

Summary:

Over southern and eastern Australia the cold front events with potential to bring widespread rain are now expected about 25 December to 29 December, 8 January to 12 January, and 15 January to 19 January. Rain events originating in the tropics and moving south are possible about 10 December to 14 December. Over Western Australia the strongest cold fronts should occur about 26 December to 30 December, 8 January to 12 January, and 15 January to 19 January.

Issue Notes - Issued Dec 11

ENSO status: Neutral IOD status: Positive SAM status: Negative Sea surface temperatures (SSTs) across the equatorial central Pacific continued to exhibit a slight warming during November. The Nino3.4 index lingered between 0.6 and 0.7 throughout the month of November. However, this has dropped to 0.4 since early December. On the other hand, the Southern Oscillation Index (SOI) recorded a value of -9.3 in November. The current outlook continues to suggest warmer than average SSTs will persist across the equatorial Pacific Ocean through the coming months, but remaining within neutral values. Seven out of eight international models maintain a warmer than average equatorial Pacific Ocean through the first quarter of 2020, none of these reaching El Nino thresholds. The IRI ENSO forecast continues to suggest a less than 40% chance of another El Nino developing over the next 6 months, with a neutral ENSO the most likely outcome. To the west of Australia, the Indian Ocean Dipole (IOD) remains in the positive side of neutral, though it has significant strength after peaking in October . All six international models maintain a positive event until January. In terms of rainfall across Australia, there is little variation to the outlook issued last month across the west. However, the climate outlook for the eastern states has seen a significant drying over the past 2 months. The current outlook now favours a clearer below average rainfall signal for the eastern states. This however, excludes any extreme weather events such as tropical cyclones in Qld or East Coast Lows. For northern Australia, the current outlook favours a late onset of the North Australian Monsoon (NAM) across the Northern Territory and Queensland. Usually, Darwin tends to see the onset of NAM around christmas day. Further south, a negative trend in the Southern Annular Mode (SAM) continues to enhance frontal activity over southern SA, Victoria, Tasmania and southern NSW. This has offset the Positive IOD in far southern Victoria and western Tasmania, which continue to see average-to-above average rainfall odds through December and early January. 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 suggests neutral odds for the second half of summer.