The climate drivers that are supporting the wetter outlooks across the nation are still in place, with the cool neutral/weak La Nina phase over the Pacific continuing to push warmer waters to the north and east of Australia (leading to the higher-than-average rainfall we are seeing once again in the short term via easterly winds).
The warmer waters persist over the Indian Ocean with the thermal gradient starting to represent the strengthening negative Indian Ocean Dipole Phase which will support widespread rainfall developing through the remainder of Winter and more into Spring 2022.
The Southern Annular Mode remains volatile, with the signals remaining volatile and of low confidence as we move through to the end of the month. This climate hustler helps to move around all that moisture across the nation and while positive, the rainfall remains heavier in the east. For rainfall to return to above average values we saw back in late May or early June, we need a negative phase to unfold.
Let's look at the latest guidance.
I will have more on this tomorrow with a broader update across the nation relating to the ENSO outlook and where we are going over the Spring and Summer on Friday. The ENSO is currently weak La Nina/cool neutral with that contributing to the warmer than normal waters over the Coral Sea and sweeping through the northern tropical waters north of the nation. The ENSO is forecast to remain unchanged through the remainder of Winter and into Spring, I think we see higher impacts from the ENSO coming into Summer where a La Nina phase will likely develop. At this time the ENSO region should resolve from the La Nina quicker next year through late Summer but that was the guidance this time last year, so here we are. Rather than going over it in great detail now I will have more on this tomorrow.
INDIAN OCEAN DIPOLE
The Indian Ocean Dipole is forecast to turn negative over the coming 6 weeks, and while it is technically negative now, the major impacts are being felt out west at the moment with the synoptic scale impacting the influence coming further east. And the SAM supporting the emergence of easterly winds redeveloping will keep the moisture coming out of the Indian Ocean peaking through WA in the coming week. As the SAM trends more neutral that will help to open the westerly wind belt back to the southern parts of the nation and we will see the moisture running through the jet stream on the northern flank of that westerly wind belt. Further along, the IOD is forecast to remain negative and peak through the Spring, so the tap will be turned on hard for the period running into Harvest nationally. The west may see lighter impacts but could feel the higher than normal moisture and rainfall via the IOD in the coming 2 months before we see conditions shift into Spring. Humidity will begin to increase over the northern tropics, especially WA and the NT with the moisture lifting into early season rainfall chances from later August and more likely throughout the Top End from September. The wet season may run about 4 weeks earlier than normal. With the IOD increasing in strength, the impact on temperatures will unfold throughout the interior of the nation from the Spring and a higher coverage of below average temperatures may linger into early Summer as a lingering impact from the IOD event.
SOUTHERN ANNULAR MODE
I have alluded that the developing issues surrounding the SAM will continue for the remainder of the next fortnight with the weak positive phase that has formed the rain events over the east coast and inland areas in the short-term moving away. The SAM tending back towards a neutral value for the first period of August, will keep the weather generally seasonal. Any westerly wind regime will support moisture moving out of the Indian Ocean and lead to more widespread falls coming through on the northern flank of the westerly wind belt. Now, the further negative the SAM trends, the further north it moves, and this will support more rainfall over the nation's southern third. If the SAM tends more positive, then we will see more rainfall developing over the east and northeast of the nation and easterly winds return. The confidence in forecasting the SAM is climatologically at the lowest point through the year.
I will have another update on this in early August.