Climate outlook for October to December
Issued 7 October 2015
Climate outlook overview
- A special update of the climate outlooks has been released due to a significant shift towards a drier October nation-wide, related to the emerging positive Indian Ocean Dipole reinforcing the strong El Niño.
- September rainfall was third driest on record for Australia. Very low rainfall has been received over the past 12 months in the southwest of Western Australia, southeast South Australia and most of Victoria.
- Due to changed conditions in the tropical Indian Ocean and the strong 2015 El Niño, the rainfall outlook for October has shown a significant shift towards a drier month nation-wide, with the southeast quarter of Australia indicating a less than 20% chance of exceeding median rainfall for the month. This means the region has a greater than 80% chance of a drier month.
- The October rainfall outlook is accompanied with high chances of warmer days and nights south of the tropics.
- October to December is likely to be drier than average across the southeast and northeast, with parts of central Australia likely to be wetter than average. Warmer days and nights are likely for Australia, except the northern tropics.
- The current outlook reflects a combination of a mature El Niño in the Pacific, and an emerging positive Indian Ocean Dipole (see the climate influences section for more information).
Chances of a drier season increase over eastern Australia
- The October outlook update shows a notable shift – up to 40 percentage point decrease in some areas – towards a drier month nation-wide, with the southeast quarter of Australia indicating a less than 20% chance of exceeding median rainfall. This means the region has a greater than 80% chance of a drier month.
- October to December is likely to be drier than average across southeast and northeast Australia. Conversely, eastern parts of WA, and southern parts of the NT show a slightly increased chance of a wetter three months.
- The current outlook reflects a combination of a mature El Niño in the Pacific, and an emerging positive Indian Ocean Dipole.
- Historical outlook accuracy for October to December is moderate over most of Australia.
Chances of warmer days and nights increase over southern Australia
- Daytime temperatures for October to December are likely to be warmer than average across the southern half of Australia, extending into central Queensland. Daytime temperatures are likely to be cooler than average in an area spanning northern WA and the central NT.
- Overnight temperatures are likely to be warmer than normal across much of the country except in parts of the tropical north which has an increased chance of cooler nights. Across large parts of southern Australia, there is a strong likelihood of above average night-time temperatures (greater than 80% chance).
- The current outlook reflects a combination of a mature El Niño in the Pacific, an emerging positive Indian Ocean Dipole, and warm temperatures in the Indian Ocean outside the tropics.
- Maximum temperature accuracy is moderate to high over most of Australia, except for a small area in far west WA, where accuracy is low. Minimum temperature accuracy is moderate to high over much of the country but patchy in the northern tropics, and parts of the east coast.
Climate influences
- A strong El Niño persists in the tropical Pacific Ocean. El Niño is usually associated with below-average winter–spring rainfall over the eastern half of Australia, with 17 of the 26 events since 1900 resulting in widespread drought for Australia.
- Until recently, the combination of El Niño with warmer than average sea surface temperatures (SSTs) in the Indian Ocean was producing roughly equal chances of a wetter or drier three months across most of the eastern half of the country, and increasing the chances of above-average rainfall across WA, SA and central Australia. However, with the emerging positive phase of the Indian Ocean Dipole (IOD) – with September values the highest since 2006 – reinforcing the El Niño signal a drier month is likely Australia-wide.
- Climate models suggest that El Niño is likely to peak towards the end of 2015, weakening in the first quarter of next year. Models have little skill forecasting beyond the following autumn, the typical El Niño–Southern Oscillation transition period. Four out of five international models suggest the positive IOD event will persist through the remainder of spring. Positive IOD events are typically associated with decreased winter–spring rainfall over southern and central Australia.
- Typically an IOD event decays in November as the monsoon trough shifts south over the IOD region, changing the wind patterns. This results in the IOD pattern being unable to form. Once this occurs, the two dominating climate drivers are likely to be El Niño and the warm Indian Ocean, which may ease the outlook back towards more even odds.
- Bureau climatologists continually monitor the climate for any significant developments, with information on El Niño/La Niña and IOD events available fortnightly via the ENSO Wrap-Up. For a summary of Pacific and Indian Ocean outlooks, please see the Climate Model Summary.
