The Bureau of Meteorology preliminary winter summary found rainfall was above average in NSW and the ACT in July and August making it the wettest winter since 2016.

This winter was one of the 10 warmest on record nationally and the bureau said temperatures were above average along the NSW coast but closer to average inland.

The bureau's manager of climate operations Andrew Watkins said the season started out very dry but NSW was hit with a late deluge of rain.

"Overall, winter was drier than average for every state except New South Wales. It was particularly wet in Gippsland in Victoria and the south coast of New South Wales," he said.

"Earlier in the winter period, conditions were drier than normal, as rain bearing weather systems were being blocked by a belt of high-pressure systems sitting across the country."

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As spring approaches, the bureau expected temperatures to be warmer than average in the ACT and NSW with an 80 per cent chance of exceeding median rainfall for both jurisdictions but was most likely across central and western NSW.

Dr Watkins said the outlook was largely driven by changes in sea surface temperatures in the tropical Pacific and Indian oceans.

"Most long-range forecasts analysed by the bureau, including from our own climate model, are indicating a La Nina could develop in the spring, which typically results in above-average winter-spring rainfall for Australia, particularly across eastern, central and northern regions," he said.

"A La Nina also typically brings cooler and cloudier days, more tropical cyclones, and an earlier onset of the first rains of the northern wet season."