Jane's Weekly Update: 12th September 2025
The major rain system that crossed NSW this week is over New Zealand on Friday with no further effects for Australia.
It delivered big falls, widespread rain, centred over NSW, as that is where the moisture and low pressure collided, driven by a low that crossed NSW. Whoever is in the path of low pressure gets the rain.
Today we have a weak disturbance crossing the southeast and a little rain in the Top End.
Over the next week we have weather systems crossing southern Australia while showers affect northeast QLD day after day all the way through.
The southern weather systems are cold fronts. These differ from a cut-off low pressure system, as they move faster and usually don't deliver as much rain.
The first collection of cold fronts crosses the southwest on the weekend, reaching the southeast on Monday/Tuesday. The second cold front crosses the southwest next Wednesday, reaching the southeast from Friday. In between these the weather pattern lets it warm up, sometimes quite significantly.
The Pacific Ocean Index has bobbed around just under zero for the past few months. The spread of the different models is still wide indicating low confidence in the forecast. One set of modelling has it crossing the La Nina threshold in October, while the others keep it Neutral, but all on the Negative side of Neutral.
We also have warm water off the coast of Queensland, so we have a source of moisture from the Pacific no matter what happens across the basin.
The Indian Ocean Index is currently in a strong Negative Indian Ocean Dipole (IOD). This week's rain system is a classic example of how this phase helps it rain, with tropical moisture pouring in from the Indian Ocean in a juicy northwest cloudband, running into low pressure and delivering widespread rain.
But as always, you need low pressure to complete that transformation into rain, and where the low moves is who gets the rain.
For the full update, don't miss this week's video, perfect if you have 12 minutes to spare: