Climate outlook for summer (December to February)
Issued 24 November 2016
Climate outlook overview
- Summer (December to February) rainfall is likely to be below average in parts of the east and above average in northwest WA.
- The December outlook shows a drier month with warmer days for most of the country.
- Warmer days and nights are likely across eastern and northern Australia, with cooler days and nights more likely in Tasmania and southwest WA.
- This outlook is strongly influenced by a climate driver called the Southern Annular Mode (also known as SAM). It is expected to be in a negative phase in December. When this happens in summertime, weather systems are further north than usual, meaning Australia experiences higher pressures than normal. This is typically associated with reduced rainfall and higher temperatures. The Pacific Ocean, though in a neutral ENSO phase, is tilting slightly towards La Niña, increasing sea surface temperatures in the western Pacific Ocean, including around northern Australia. This may be raising the likelihood of increased rainfall over northwest WA during summer.
Dry December likely for most of Australia
- December is likely to be drier across most of mainland Australia, with a 70 to 80% chance of below average rainfall across most of eastern Australia.
- Summer (December to February) rainfall is likely to be below average across parts of eastern Australia and above average in northwest WA.
- The current outlook reflects a negative Southern Annular Mode.
- Historical outlook accuracy for summer rainfall is moderate to high over most of WA, and moderate over the eastern mainland. Elsewhere, accuracy is low to very low.
Warmer summer likely for eastern Australia
- Summer (December to February) days and nights are likely to be warmer than average in the east and north of Australia and cooler than average in Tasmania and southwest WA.
- There is a particularly high chance of summer having a warm start for most, with much of Australia likely to see warmer daytime temperatures in December.
- The current outlook reflects a negative Southern Annular Mode and a weak La Niña-like pattern in the Pacific Ocean, including warmer than average waters to the northwest of Australia.
- Maximum temperature accuracy is moderate over western and eastern parts of Australia and low across central regions and western Tasmania. Minimum temperature accuracy is moderate over most of Australia.
- The El Niño–Southern Oscillation (ENSO) remains neutral, but continues to show some weak La Niña-like attributes, including warmer than average waters to the north and west of Australia. This may be contributing to some wetter conditions in parts of northwest Australia.
- The negative Indian Ocean Dipole (IOD) event has ended, which means its influence on Australian climate has reduced.
- In the shorter term, a northerly shift in the average position of westerly winds and high pressure systems (also known as the "Southern Annular Mode", or "SAM") is forecast for December. When this northward shift (a negative SAM phase) occurs in summer, this typically means much of Australia becomes drier and warmer than usual.
- In addition to the shorter-term natural drivers, 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.