Weather

Indian Ocean fuelling some big rain systems

Written by Jane Bunn - Jane's Weather | May 30, 2025 12:00:55 AM

We've had a big rain system cross through the northwest and NT over the past few days. That lies over Queensland now and continues there for the weekend (without the significant falls that we saw further west).

Meanwhile, the next big rain system affects the west for late in the week into the early weekend. This has tropical moisture meeting up with low pressure to produce widespread rain from the Pilbara through to the south.

It's dry in the southeast as a high moves through.

The remains of the western rain system head east early next week. Yet again the drought parts of SA and Victoria miss out thanks to high pressure. There is a little more rain as you head further east (fed by the warm waters to our east) but nothing significant. 

Meanwhile, yet another big weather system affects the west. This is a long lasting one - pretty much from Monday to Friday next week. Again, tropical moisture and low pressure working together to bring widespread rain from the Pilbara through to the south.

Remember in a recent update, the Euro Week 2 outlook had rain spreading across the country and into the southeast?

Well, that may actually happen - later next week.

This big, juicy system in the west could spread across the south without completely fizzing out, as the high moves enough out of the way to let it happen. Not just low pressure (like we had last time that didn't do much for those inland in SA or Victoria), but with a tropical connection - the key ingredient we need to make it rain.

What could go wrong? Well, it is a full week away, and that's a long time in meteorology. But it is one to watch very closely.

Potential rainfall over the next week

Looking further afield, and eagle eyes will have seen the hint of a change in the Indian Ocean box over the past few weeks. Now there is a lot more blue developing, and that is the catalyst for a big shift in the Indian Ocean.

We already have warm water between Indonesia and northwestern Australia, and the current rain systems have tapped into that to bring big falls where high pressure doesn't block it - but this change in the Indian Ocean steps it up further.

Sea Surface Temperature Anomaly (SSTA)

The forecast is for the recently 'Positive', and now on the 'Positive side of Neutral' ocean to rapidly head towards 'Negative' and cross the threshold, as we go through June and July.

This increases that push of moisture from the northwest.. it enhances those big, juicy northwest cloud bands.

The question is - will the highs move out of the way to let low pressure meet up with that moisture?

There is some hope, as a Negative Indian Ocean Dipole does encourage the highs to become less dominant... so the future may be looking a lot brighter (ie wetter!).

Indian Ocean Outlook

For an in depth analysis, here is this week's video:

 

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