The Otago Regional Council is urging farmers to consider the potential impacts of an El Nino summer and its effects on farm operations, soil moisture and water supplies.
Council science manager Tom Dyer said Niwa had forecast a 100% chance of El Nino between October and December and a more than 95% likelihood of it persisting through summer.
The river flows and soil moisture content in Otago were normal or slightly higher than normal for this time of year.
"The 35-day forecast is for slightly drier conditions than normal, although we do not expect significant drought-related issues across much of the region over that timeframe."
Northeastern areas of Otago could start to dry out.
River and rainfall predictions might be close to or above average for Otago but long periods of wind could dry out soils in a short time.
During El Nino, river levels and rainfall were expected to be average to below average for East Otago and average to above average for inland Otago.
Council regulatory acting manager Joanna Gilroy said farmers needed to consider making a plan including contingencies, and "act on it earlier rather than later".
"Having a plan now will help to support making decisions later on.
"Plenty of thought should be given to water needs over summer, how water will be managed and what feed requirements there might be."
