The wet and warm signal for spring still continues from all global climate agencies and the climate drivers. The weather will get wetter as we go through the season, but we may find the weather warming up ahead of the wetter signal.

Seasonal Outlook - Rainfall - August to October 2021

% chance of deviating from the median rainfall for the period

The seasonal outlook for NSW continues to show a wet signal. That is thanks to the Indian Ocean dipole be in a negative phase, which is allowing more moisture to be transported through the atmosphere from northwest to southeast through interior parts of the nation and stacking up on and west of the divide.

We saw back in 2016 the impacts of a strong negative Indian Ocean Dipole, which produced flash flooding and significant riverine flooding through many parts of southern and central NSW. This outlook is showing a slightly milder dipole event, but the impacts are the same where flooding is still a moderate to high chance throughout the spring season.

That means over the coming two to four weeks through August we will start to see the pattern deviate from the previous six weeks where we have had a frontal barrage in the westerly wind regime. The pattern is likely to shift the westerly wind belt a little further south, not excluding the region from having frontal passages move through, but they will have a lesser impact as we go through this period. Moisture being drawn in ahead of these frontal systems over the south of the nation is the feature to watch.

As the temperatures across the nation continue to warm, the atmosphere can hold more moisture, that means more rain events will start to emerge from central and northern WA and then through the middle part of this seasonal outlook.

As we go through late September through October the storm season officially kicks off, this is in part due to the heat values over the inland portions of Queensland the Northern Territory and Western Australia allowing troughs to develop. As that develops these troughs will become the focal point for thunderstorm activity which will continue the rainy signal in between major rain events, which will stop the ground from drying out sufficiently to lower the risk of flooding.

It is through incremental rainfall that flooding develops, a bit like what we have seen over the past 10 days light to moderate rainfall pushing through frequently allows the ground to stay saturated.

The peak of the rainfall is expected through mid-September through most of October that is in line with the Indian Ocean dipole peaking, which is being modelled fairly well by international global weather agencies.

Finally on the rainfall, we will have to watch how early the northern tropics ignite with showers and thunderstorm activity in their predicted early build-up, because that could add more moisture into the atmosphere not just from the northwest and west of the nation with the Dipole influence, but also now from the north and the northeast. Especially as winds shift more northeast to easterly.

Seasonal Outlook - Temperature - August to October 2021

% chance of deviating from the median temperature for the period

For NSW we are seeing temperatures above average for most of August but with increased rainfall an cloudiness expected to developed through September and October the temperatures are likely to be near seasonal or below average for the best part of September more likely into October.

That pattern does continue into November and December.

The big problem also associated with these outlooks is the high levels of humidity which may lead to significant increase in the risk of fungal issues for the food bowl.

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