An El Nino event is tightening its grip on Australia's climate and increasing the risk of drought.

The Bureau of Meteorology says the El Nino, a warming of the sea surface in the central and Eastern Pacific, is strengthening.

Its fortnightly El Nino Southern Oscillation Wrap-Up, released on Tuesday, says sea surface temperatures have remained at least 1C above average for six consecutive weeks.

International climate models surveyed by the Bureau of Meteorology indicate further consolidation of the El Nino is likely, the wrap-up said.

"El Nino events typically strengthen during the second half of the year, reaching full strength during late spring or early summer," it said.

"It is not possible at this stage to determine how strong this El Nino will be."

The bureau has already predicted that the El Nino will continue to strengthen until the end of 2015.

El Ninos generally cause below-average winter and spring rainfall in Australia, particularly in the east.

But an El Nino's strength does not always correlate to the intensity of any drought.

Drought conditions already exist in parts of Victoria, Queensland, South Australia and NSW.

A looming disparity in sea surface temperatures in the Indian Ocean could further intensify any drought in Australia, the bureau said.

The bureau said three out of five international climate models now predict the eastern side of the Indian Ocean will cool compared with the west in the spring, increasing the chances of below-average rain in central and southern Australia.

That prediction is up from two out of five just two weeks ago.