Autumn climate drivers to steady soon

This means WA's climate shouldn't be influenced by weather events such as El Nino, La Nina, or an Indian Ocean Dipole (IOD) which produce specific weather conditions.

The report is published by the Department of Primary Industries and Regional Development (DPIRD) and the Bureau of Meteorology (BoM).

DPIRD senior research scientist Dr Meredith Guthrie is feeling more optimistic about the upcoming season.

"It doesn't mean autumn is going to be average, it means anything is possible," Dr Guthrie said.

"It's a better outlook for this year."

However, Dr Guthrie said autumn was the most difficult time to make predictions about climate drivers.

The autumn predictability barrier means two major climate and weather influences, the Pacific Ocean and the Indian Ocean, typically don't fall one way or another, or reveal the effects they will have on the growing season.

In addition to this, unexpected wind bursts can easily push the system, called the El Nino Southern Oscillation or ENSO, into either El Nino, La Nina, or neutral.

"All models have low skill at predicting past autumns," Dr Guthrie said.

"Models are at their highest skill in winter.

"But if all these different models are saying the same thing, it's probably a good idea to plan for that."

The current climate situation is showing that last year's positive IOD has decayed, however two forecast models indicate the positive IOD may develop again in June.

A positive IOD is generally associated with drier winter and spring conditions, lower rainfall, and warmer temperatures within the South West Land Division (SWLD).

The last positive IOD event was in 2023, which was combined with El Nino.

The combination placed 2023 in the lowest 20-30 per cent of years on record for rainfall.

The ENSO outlook shows that Australia is currently in El Nino, which is expected to continue until May.

Four out of seven models indicate that ENSO will return to neutral by the end of April, and all models indicate neutral by May.

"We haven't had a neutral ENSO for a long time, so we're due for one," Dr Guthrie said.

Three out of seven models surveyed by the BoM are indicating a La Nina to develop in the Pacific Ocean by July.

Dr Guthrie said a La Nina alone didn't have much effect on the SWLD.

The last time Australia was in La Nina was in 2022, which was combined with a negative IOD, producing ideal cool and wet growing conditions for this year.

However Dr Guthrie said the effects of these climate drivers weren't always consistent, such as 2010, which also had a La Nina and negative IOD combination.

"That brought quite poor rainfall across the SWLD because we had another climate driver, the Southern Annular Mode (SAM) which was having a much bigger impact," she said.

"The problem with SAM is that you can't forecast it very far out - about two weeks - whereas ENSO can be forecast five months ahead of time.

"The SAM is more volatile."

Out of 20 national and international models, 10 are indicating below average median rainfall across the South West Land Division for autumn.

So far, the rainfall from January 1 to February 28 has dramatically varied from town to town, with Esperance recording 102 millimetres of rainfall, while some towns along the west coast only recorded 5mm or less.

Both maximum and minimum temperatures are likely to be above average for all of Australia, and minimum temperatures are far more likely to be unusually high in WA for the autumn season.

Dr Guthrie said the position of the SWLD in relation to the rest of the world made the climate more varied.

"It's just our corner of the world, if we were on the east coast it would be completely different," she said.

"Our part of the world is much more influenced by the Indian Ocean than the Pacific Ocean."