Climate outlook for December to March

Climate outlook overview

  • Drier than average summer likely for eastern Australia, but wetter for parts of the west coast. 
  • Summer daytime temperatures are very likely to be above average across Australia. 
  • Summer nights very likely to be warmer than average except in the southeast. 
  • Climate influences—a strong positive Indian Ocean Dipole (IOD) and negative Southern Annular Mode (SAM) continue to influence the outlook. Both influences are expected to progressively weaken, then dissipate during the first half of the season.

Drier than average summer likely for the east, wetter for the west coast

  • The outlook for December shows much of the country is forecast to be drier than average for the month, with parts of northern Queensland and the Top End of the NT most likely to be dry. Parts of the Gascoyne and Pilbara in WA have a slightly increased chance of being wetter than average. 
  • For summer as a whole (December to February), the dry signal contracts to the eastern States. Conversely, much of the western WA coastline has a slightly increased chance of above average rainfall in summer. 
  • While outlooks for drier than average conditions may ease for some areas heading into 2020, several months of above average rainfall would be needed to see a recovery from current long-term rainfall deficiencies.

Warmer days and nights likely for summer

  • Daytime temperatures for summer (December to February) are very likely to be warmer than average for Australia, except for western Tasmania. Similarly, January to March is likely to be warmer than average for almost all of Australia. 
  • Cooler nights for the southeast are likely in December, with warmer than average nights likely across much of the west, north and east. 
  • December to February nights overall are forecast to be warmer than average almost nation-wide. However, southeast SA, southern and central Victoria, and Tasmania have roughly equal chances of warmer or cooler than average nights. 

Climate influences

  • The strong positive Indian Ocean Dipole (IOD) continues to influence Australia's weather, but has weakened over the past four weeks. Typically, a positive IOD means below average rainfall for much of central and southern Australia, and warmer than average temperatures for the southern two thirds of Australia. This is broadly consistent with the current outlook.
  • IOD events typically have little influence on Australian climate from December to April, meaning the positive IOD's contribution to the drier outlook should start to reduce in summer. However, the current positive IOD is so strong, and the movement of the monsoon into the southern hemisphere so late, the positive IOD is likely to take several more weeks to decline, and could persist into mid-summer.
  • A negative phase of the Southern Annular Mode (SAM) is expected to continue until at least late December. A negative SAM in summer tends to bring drier conditions to parts of eastern Australia, but wetter conditions to western Tasmania. This rainfall pattern is most notable in the outlook during December. 
  • While tropical Pacific Ocean temperatures are likely to stay warmer than average, the El Niño–Southern Oscillation (ENSO) is expected to remain neutral until at least early 2020, and therefore is unlikely to influence Australian climate.
  • In addition to the natural drivers such as ENSO and the IOD, Australian climate patterns are being influenced by the long-term increasing trend in global air and ocean temperatures.

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