Climate outlook for summer (December to February)
Issued 30 November 2017
Climate outlook overview
- The summer (December to February) rainfall outlook, issued 30 November 2017, shows no strong swing towards a wetter or drier conditions for most of Australia. Parts of the Pilbara and Gascoyne in WA, and coastal regions of southeast Australia, are likely to have a wetter than average summer, while the northern Cape York Peninsula may be drier than average.
- December is likely to be wetter than average for southeast Australia, extending up into southwest Queensland.
- Summer daytime temperatures are likely to be warmer than average for southeast, central and far northern Australia.
- Summer nights are likely to be warmer than average for northern, central and southeastern Australia and along the southern WA coastline.
- The tropical Pacific Ocean is approaching La Niña thresholds, and our ENSO Outlook is at La Niña ALERT.
- This likely 2017-18 La Niña event is forecast to be short-lived and weak, with sea surface temperature patterns in the western Pacific and eastern Indian Ocean not typical of La Niña. As a result, there's little push towards widespread wetter conditions across much of the country. See the Climate Influences section for more information.
Wet start to summer likely for southeast Australia
- Parts of the Pilbara and Gascoyne in WA, and coastal regions of southeast Australia are likely to have a wetter than average summer. Northern Cape York Peninsula in Queensland is likely to be drier during summer. The summer rainfall outlook shows no strong swing towards wetter or drier conditions for most of Australia.
- December is likely to be wetter for southeast Australia, extending up into southwest Queensland. Parts of southern WA are likely to have a drier December.
- The tropical Pacific Ocean is approaching La Niña thresholds, and a La Niña ALERT is active. However, forecast patterns in the western Pacific and eastern Indian Ocean are not typical of La Niña. As a result, there's no strong push towards wetter conditions across much of the country. The wetter signal in December across the southeast is likely a result of positive Southern Annular Mode (SAM) phase, which acts to draw tropical air southwards and increase onshore flow.
- Historical outlook accuracy for summer is moderate for eastern and western parts of Australia, but generally low elsewhere. See map for more detail.
Warmer summer likely for southeast and central Australia
- Summer daytime temperatures are likely to be warmer than average for most of SA, Victoria, Tasmania, the southern NT, and far northern Australia.
- Summer nights are likely to be warmer than average for northern, central and southeastern Australia, and along the southern WA coastline.
- Historical accuracy for maximum temperatures is moderate over WA, the Top End of the NT, and the eastern mainland. Elsewhere, accuracy is low. Minimum temperature accuracy is moderate for most of Australia except the central NT and parts of the Gulf of Carpentaria.
Climate influences
- The Bureau's ENSO Outlook is at La Niña ALERT, as the tropical Pacific approaches La Niña thresholds. Most international models maintain a weak La Niña until early autumn.
- Typically when the tropical Pacific cools towards La Niña levels, the western Pacific and seas around northern Australia warm significantly, but models suggest this is not likely to occur this summer.
- Likewise, La Niña periods typically see warmer than average waters develop in the eastern Indian Ocean. This season, near average to cooler waters are forecast to remain in this area, while warmer waters remain off Africa.
- The combination of ocean patterns, and the likely weak La Niña itself, is why Australia does not have significant and widespread increased chances of a wetter and cooler summer.
- Unlike El Niño, the strength of La Niña events are typically related to the strength of its effect; for example, weaker La Niña events typically have a weaker effect on Australian rainfall than stronger events.
- The wetter signal in December across the southeast is likely a result of a positive Southern Annular Mode (SAM) phase, which acts to draw tropical air southwards and increase onshore flow. Positive SAM phases are more likely to occur with La Niña.
- In addition to the natural drivers such as the El Niño–Southern Oscillation and the IOD, Australian climate patterns are being influenced by the long-term increasing trend in global air and ocean temperatures.
- 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.
