The impacts of the monster El Nino in the Pacific are likely to intensify across much of Australia, including worsening drought and an elevated bushfire threat, after conditions that were nullifying its effects suddenly retreated, the Bureau of Meteorology said.

In a rare move to reflect "a significant shift towards a drier October nationwide", the bureau on Wednesday updated its three-month seasonal outlook for October to December just a fortnight after it was issued.

The main shift has been in the temperatures of the Indian Ocean, with the eastern region rapidly cooling off compared with the west, a pattern that tends to choke off rainfall streaming across the Australian continent from north-west Western Australia.

"The Indian Ocean has gone from masking to reinforcing the El Nino in Australia," David Jones, head of climate analysis at the bureau, said. "We've seen this sharp escalation in the impacts."