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Seasonal Climate Outlook

May 2026

Summary

For the South West Land Division (SWLD) models indicate below median for May to July through to August to October. Both daytime and night-time temperatures are expected to be warmer than normal for May to July, and winter (June to August) 2026.

Recent conditions

Rainfall in April was average for the majority of the SWLD, with DPIRD weather station Magenta (south of Newdegate) receiving 126 mm and DPIRD Pindar South weather station only receiving 5 mm.
Current outlook indicates an El Niño, a positive Indian Ocean Dipole, and a positive Southern Annular Mode (SAM). All 3 combined are likely to reduce winter rainfall in the SWLD (although a positive SAM typically brings higher rainfall to Esperance). If the El Niño and positive IOD persist into spring, spring rainfall is also likely to be reduced, along with higher than normal daytime and night-time temperatures.

Outlook summary

Rainfall summary

Rainfall in April was average for the majority of the SWLD, with DPIRD weather station Magenta (south of Newdegate) receiving 126 mm and DPIRD Pindar South weather station only receiving 5 mm. Current soil water map shows good soil moisture for some parts of the SWLD.

Figure 1: Rainfall (mm) totals for 1 April to 2 May 2026 in the SWLD. Magenta recorded the highest total of 126 mm and the lowest total is Pindar South with 5 mm.

Figure 2: Rainfall decile map for 1-29 April 2026 in the SWLD, indicating decile 4-7 for the majority of the SWLD.

Figure 3: Plant available soil water map for the SWLD using rainfall up to 29 April 2026, uses the two-layer fallow Ritchie model and represents the mean of 10 soil types. The map indicates dry conditions in some parts.

Break of the season

Traditionally, the ‘break of season’ was defined as the first rainfall event delivering 25 mm over 3 days after 25 April. This has since been refined to 15 mm over 3 days from 1 April. As there was a significant rain event on 28 March, the map for 2026 is using 15 mm of rain since 28 March. Using data up to 29 April, the map shows that a break has occurred for the majority of the SWLD.

Historically, the average date for the majority of the SWLD is early to mid May, so there is still time for a break to occur within the normal range. The earliest average break of season is 14 April for Barrett Meadows weather station (in the shire of Albany), and the latest is 28 May for Dartmoor weather station (in the shire of Chapman Valley).

Break of season map for SWLD as at 29 April

Figure 4: Break of season map for SWLD using data up to 29 April 2026, where sowing rule is defined as 15 mm over 3 days since 28 March. Indicating that the majority of the SWLD has received a break to the season.

Figure 5: Average date of break of season for SWLD, where sowing rule is defined as 15 mm over 3 days since 1 April.

Climate drivers

ENSO and IOD outlook

The World Meteorology Organisation summary of 12 climate models, including the Bureau’s ACCESS model, shows that all 12 indicate an El Niño developing in the Pacific Ocean from June. This event is forecast to persist into spring and may even continue into 2027. The IOD outlook shows 7 out of 12 models indicating a positive IOD developing in July, with all models (except for the Bureau’s) persisting through to October. An El Niño combined with a a positive IOD can reduce winter-spring rainfall in the SWLD.

World Meterology Organisation forecast of El Nino

Figure 6: World Meteorology Organisation forecast showing all 12 models indicate an El Niño developing in June and persisting until at least October.

Forecast of Indian Ocean dipole mode index

Figure 7: The Indian Ocean Dipole index indicating positive IOD developing in July 2026. Skill is lowest at this time of the year. European Centre for Medium Range Weather Forecasts SST map does not indicate a positive IOD forming.

Southern Annular Mode (SAM)

The SAM is a major influence on winter rainfall in the SWLD. As it is only forecast one month ahead, mean sea level pressure anomaly forecasts can be used to indicate the likely position of the SAM. The Bureau’s mean sea level pressure forecast for winter (June-August) shows a positive SAM, with higher than normal mean sea level pressure over Australia. This pattern is likely to reduce winter rainfall across most of the SWLD, as cold fronts track further south, while increasing rainfall in the Esperance region.

Figure 8: Mean sea level pressure forecast for June to August 2026 for the Bureau of Meteorology, indicating a positive SAM.

The combination of an El Niño, positive IOD, and a positive SAM is likely to reduce winter rainfall in the SWLD (although a positive SAM typically brings higher rainfall to Esperance). If the El Niño and positive IOD persist into spring, spring rainfall is also likely to be reduced, along with higher than normal daytime and nighttime temperatures.

Rainfall outlooks

Three-month and single-month rainfall outlooks are derived from a range of national and international climate models. The outlooks are presented as the probability of rainfall being below, above, or neutral relative to the median rainfall. (Note: A neutral outlook suggests that extreme wet or dry events are less likely, and a wide range of rainfall amounts remains possible). To provide a more localised perspective, the SWLD has been divided into 2 regions, allowing for tailored rainfall outlooks specific to each area.

Figure 9: Rainfall outlooks are in 2 sections based on location in the SWLD ̶ the first group includes Central West and Central Wheatbelt forecast districts, while the second group covers Lower West, South West, Great Southern, South Coastal and South East Coastal forecast districts.

Rainfall outlooks for the Central West and Central Wheatbelt forecast districts of the SWLD

Single month

A summary of 14 national and international models shows that 9 models indicate neutral chances of exceeding median rainfall for May 2026. There is also neutral model consensus for June and October. A neutral outlook suggests that extreme wet or dry events are less likely, and a wide range of rainfall amounts remains possible. For July to September, there is model consensus for below median rainfall. It is important to note that forecasts are less accurate the further ahead they look.

One month rainfall outlook central west and central Wheatbelt

Figure 10: Single month model summaries of rainfall outlooks for the Central West and Central Wheatbelt forecast districts of the SWLD up to October 2026. Model consensus is for neutral chances of exceeding median rainfall for May, June and October. Model consensus is for below median rainfall for July, August and September. Note that forecasts are less accurate the further ahead they look.

Three month

A summary of 17 national and international models shows that for May to July 2026, 9 models indicate below median rainfall. Further ahead, this model consensus continues through to August to October. Note that forecasts are less accurate the further ahead they look.

Rainfall outlooks central west and central Wheatbelt

Figure 11: Three month model summaries of rainfall outlooks for the Central West and Central Wheatbelt forecast districts of the SWLD up to August to October 2026. Model consensus is for below median rainfall. Note that forecasts are less accurate the further ahead they look.

Rainfall outlooks for the Lower West, South West, Great Southern, South Coastal and South East Coastal forecast districts of the SWLD

Single month

A summary of 14 national and international models shows that 8 models indicate neutral chance of exceeding median rainfall for May 2026, suggesting that extreme wet or dry events are less likely, and a wide range of rainfall amounts remains possible. There is no model consensus for June. Model consensus is for below median rainfall for July through to October. Note that forecasts are less accurate the further ahead they look.

One month rainfall outlooks for lower west, south west, great southern, south coastal and south east coastal

Figure 12: Single month model summaries of rainfall for the Lower West, South West, Great Southern, South Coastal and South East Coastal forecast districts of the SWLD up to September 2026. Model consensus is for neutral chance of exceeding median rainfall for May. Model consensus for below median rainfall for July to October. No model consensus for June. Note that forecasts are less accurate the further ahead they look.

Three month

A summary of 17 national and international models shows that for May to July 2026, 11 models indicate below median rainfall. This model consensus continues through August to October. Note that forecasts are less accurate the further ahead they look.

Figure 13: Three month model summaries of rainfall outlooks for the Lower West, South West, Great Southern, South Coastal and South East Coastal forecast districts of the SWLD up to August to October 2026. Model consensus is for below median rainfall. Note that forecasts are less accurate the further ahead they look.

Important disclaimer
The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.