Seasonal Climate Outlook

Recent climate

December rainfall in the SWLD was above average along the coast, near average in the central wheatbelt and below above in the eastern wheatbelt. December maximum and minimum temperatures were near average or above average.

In December the atmospheric pressure was near normal over the south-west. The Indian Ocean sea surface temperatures north-west and west of WA were cooler than normal.

Pacific Ocean climate patterns indicate a weak La Niña persists in the tropical Pacific. The event is expected to be short-lived, and end in the southern autumn of 2018. Past late developing La Niñas have had little influence on south-west Western Australia (SWWA) in summer.

The Indian Ocean Dipole (IOD) is neutral. IOD events are typically unable to form between December and April due to the influence of the monsoon trough over the tropical Indian Ocean. See the Bureau of Meteorology’s IOD and Pacific Ocean interaction for details.

The Southern Annular Mode (SAM), also known as the Antarctic Oscillation (AAO), describes the north–south movement of the westerly wind belt that circles Antarctica, dominating the middle to higher latitudes of the southern hemisphere. SAM is currently positive and is expected to remain positive until the end of January. In a positive SAM event, the belt of strong westerly winds contracts towards Antarctica. In spring and summer, a strong positive SAM can mean that southern Australia is influenced by the northern half of high pressure systems and hence there are more easterly winds bringing moist air from the Tasman Sea to south-east Australia. This increased moisture can turn to rain as the winds hit the coast and the Great Dividing Range. However, a positive SAM generally has little influence on spring/summer rainfall in the SWLD.

The table below gives a summary of past month and three month SWWA climate conditions and can be used as an indication of what is likely to occur in the near future, if climate conditions follow the current pattern.

Climate indicator Past month Past three months
SWWA Rainfall Above average to average Generally average
SWWA mean temperature Near average Above average
SWWA atmospheric pressure Near normal Near normal
Indian Ocean sea surface temperature Cooler Cooler
El Niño/Southern Oscillation (ENSO) La Niña La Niña
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Positive Positive