Seasonal Climate Outlook

Recent climate

April rainfall was generally below average for the grainbelt. The last three months, February-April rainfall was below average for the northern and southern grainbelt, average for the eastern grainbelt and above average for the Esperance region. April maximum and minimum temperatures were average to above average. Despite the rainfall in late January and early February, there is little plant-available soil water in most areas. The latest modelled plant available soil water map (6 May) shows very low levels of stored soil water in the majority of the grainbelt with good levels in western parts of the Esperance shire.

Plant available soil water map for 6 May 2018. Showing very low levels for the majority of the grainbelt.
Plant available soil water map for 6 May 2018 

In April the atmospheric pressure was near normal over the southwest. The Indian Ocean sea surface temperatures north-west and west of Western Australia are also near normal.

In the tropical Pacific, the El Niño–Southern Oscillation (ENSO) remains neutral. All climate models indicate the tropical Pacific Ocean will continue to warm slowly, but temperatures will remain close to average through the southern hemisphere winter. By September, two of the eight models suggest ocean temperatures may approach El Niño thresholds.

The Indian Ocean Dipole (IOD) is currently neutral. Most models indicate a neutral IOD is likely for autumn and early winter. However, three of six models suggest an increased likelihood of a negative IOD developing by July. Typically during negative IOD events, winter–spring rainfall is above average over southern Australia. However, forecast accuracy for the IOD is lower during the autumn compared to other times of the year and should be viewed with some caution. 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 near neutral and is expected to remain this way until the end of May.

The table below gives a summary of past month and three month south-west Western Australia (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 Below average Generally below average
SWWA mean temperature Average to Above average Above average
SWWA atmospheric pressure Near normal Near normal
Indian Ocean sea surface temperature Near normal Cooler
El Niño/Southern Oscillation (ENSO) Neutral Neutral
Indian Ocean Dipole (IOD) Neutral Neutral
Southern Annular Mode (SAM) Negative Positive

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