The normally easterly trade winds have weakened in the past two weeks and temperatures are again picking up in a broad region of the central and eastern equatorial Pacific, the bureau said in its fortnightly update.

If the winds remain weak, “there could be a renewed push to an El Nino”, said Robyn Duell, a senior climatologist at the bureau. “It’s still a real possibility for 2014.”

El Nino years often see above-average temperatures across southern Australia and below-average rainfall across the south and eastern inland parts of the country.

The El Nino-Southern Oscillation phenomenon is watched closely by weather agencies around the world because of the dominant role El Nino and its counterpart, La Nina, play in setting global conditions.

Two weeks ago, the bureau downgraded the prospect of an El Nino this year to about a 50-50 chance, a shift echoed since by the US Climate Prediction Centre although it rates the likelihood as about a 65 per cent possibility.

Weather watching

The Australian bureau, though, says the prospect of an El Nino remains “at least 50 per cent”, with five of the eight major climate models pointing to such an event forming by the spring.

“We are really watching the trade winds over the next fortnight or so, which will be key to telling us what will happen in the spring,” Ms Duell said.

An El Nino would not be welcomed in parts of Australia which are already dry.

Rainfall deficiencies have increased in their extent over south-eastern Queensland and north-eastern NSW, the bureau reported last week.

A region from Bundaberg in Queensland to Coffs Harbour in NSW and inland to Roma and St George has had its driest year since 1901-02, based on area-averaged rainfall.

Southern Australia, though, has not been as dry, with conditions in the Indian Ocean lately favouring above-average rainfall.

A so-called negative Indian Ocean Dipole (IOD) - where waters in the eastern regions of the ocean are relatively warm and those in the west relatively cool – has been a countering influence to the Pacific in recent months, the bureau said.

“It’s hard to know which will be the stronger influence,” Ms Duell said.

Model outlooks, though, indicate the negative-IOD is likely to be relatively short-lived, with more neutral conditions setting in by spring, the bureau said.

The dry and warm conditions in eastern Australia have already seen an early start to the fire season with the NSW Rural Fire Service reporting more than 440 fires in the first week of August, mostly in the northern parts of the state.

Areas around Sydney have also been relatively dry although the 21 millimetres of rain recorded in the 24 hours to 9am Tuesday were the city's best falls in about four months.