The Bureau of Meteorology has activated its El Nino watch, with the likelihood of such a system developing increasing to 50% – double the normal chance.

Sea surface temperatures in the eastern Pacific have been warming slowly since April, and below-surface temperatures are warmer than average, a common precursor to an El Nino.

Acting Manager of Long-Range Forecasting Robyn Duell says five out of eight models indicate ocean warmth is likely to reach El Nino thresholds in the southern spring.

Potential effects in an El Nino effect in Australia include reduced rainfall, warmer temperatures, a shift in temperature extremes, increased frost risk, reduced numbers of tropical cyclones, a delay in the onset of the wet season in northern Australia, an increased fire danger in south-eastern Australia, and decreased alpine snow depths.