Monday 11th Jul, 11:55 PM

12th July Seasonal and Rain Update - every Tuesday and Friday

In this series I'll take you through the drivers of our weather, highlighting any changes over time and things to watch out for (every Tuesday and Friday). It covers weather elements like temperature and rainfall, and how they are driven by moisture from the Pacific and Indian Oceans, as well as bursts of energy (SAM and MJO).

Every Tuesday and Friday I take you through the drivers of our weather, highlighting any changes over time and things to watch out for. It covers weather elements like temperature and rainfall, and how they are driven by moisture from the Pacific and Indian Oceans, as well as bursts of energy (SAM and MJO).

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Updated twice weekly as that is when most indicators update.

THE NEXT WEEK

The current weather maps shows a cold front sliding across the southeast, high pressure over the northern Bight, and a cold front approaching the southwest. The conveyor belt of fronts will keep progressing eastwards across the south, broken up by high pressure. High pressure dominates the north (typical for winter), but if the high moves so that winds turn onshore there is precipitation there.

That pattern keeps the rain in the south and gives much of the north a break, except when winds are onshore, but it doesn't produce a lot of precipitation without strong low pressure. There is the slight potential for a deep low off NSW mid next week. The next 8 days rain:

From Saturday to next Friday Australia is dominated by drier than average weather. However, the NSW low is showing up late in the period, and the cold fronts crossing the south keep rainfall close to average - but not strong enough for Tasmania's west to see the usual amount:

Clear and colder than average nights are likely through a large part of the inland, but not in the southwest with the frontal activity:

The colder than average weather is weakening, but still present in the far east and north:

THE DRIVERS OF THIS PATTERN

Looking at the two boxes of interest in the Pacific and Indian Oceans, the Pacific is now only very lightly shaded cool blue (and certainly not near a warm orange, only hints of yellow), a sign of neutral conditions but slightly negative.

The Indian box's area of blue continues to deepen in colour as it has over the past few weeks. This is why we have entered a Negative Indian Ocean Dipole (the Indian equivalent of La Nina):

So, the Pacific Ocean pushes a little moisture towards Australia (less moisture than we had over summer and autumn, but not taking the moisture away), while the Indian Ocean is increasing the moisture available to send towards Australia.

This is helped by warm oranges around much of Australia to help drive that moisture in... and the very warm Tasman Sea encourages low pressure to form just off the coast (one of the ingredients for flooding rain).

The Pacific Ocean shows we are out of La Nina (green area) but nowhere near El Nino (brown area). The Consensus of the models shows that we may enter another La Nina towards the end of the year (which would be our third in a row). No model likes El Nino:

PACIFIC OCEAN (EL NINO/LA NINA)

The Indian Ocean models are all singing a very similar tune. In the past month we have done a deep dive, well into a Negative Indian Ocean Dipole (green area). All models predict a strong negative IOD for the rest of the year, coming out of it as we naturally do in summer:

INDIAN OCEAN (IOD)

This means lots of moisture will be pushed towards Australia for the rest of the year from the Indian Ocean, and a little from the Pacific, while the waters around Australia encourage moist air too.

But... moisture is just one part of the rain equation. You can have bucket loads of it, but if there isn't any low pressure in your area, it won't produce any rain (except for lighter falls near the coast in onshore winds).

So, we look at SAM and MJO to see what low pressure is likely to do.

SAM tells us if the weather map is more likely to show strong cold fronts coming up from the south (bottom green), or troughs and lows in NSW/southern QLD latitudes with weaker cold fronts (top green), or a wishy washy pattern (white):

The MJO is a pulse of tropical energy, and whenever that comes near Australia it acts to bring the lows and moisture together. This signal looks to be going back into neutral, then possibly into a drier phase:

The next update is due on Friday morning. Make sure you are signed up (free or premium membership) to get them delivered to you. And as always, you can see each of these graphics and more information about them under our Rain Outlook and Seasonal Outlook pages under Jane's Update.