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More rain: climate models point to a La Nina

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Climate models monitored by the Bureau of Meteorology are increasingly pointing to a La Nina event forming this year, raising the likelihood of above-average rainfall.

The bureau has shifted its El Nino-Southern Oscillation outlook dial to “La Nina watch”, with three models indicating an event could form by late winter and another two suggesting thresholds could be approached during early spring.

“After a wet start to the year in southeast Australia, June has been drier than normal,” Senior Hydrologist Paul Feikema said last week. “However, with a shift to La Nina watch, July to September may see wetter than average conditions return,”

The most recent La Nina to have a significant impact in Australia lasted from 2010-2012, covering the period when the Brisbane floods and torrential rainfall in nearby regions generated insurance claims topping $1.5 billion.

Typically, the event brings above-average winter-spring rainfall, particularly across eastern, central and northern regions, cooler days, more tropical cyclones, more snow and an earlier onset of the tropical wet season.

The bureau’s outlook suggests a 50% chance of an event occurring, twice the normal likelihood.

The bureau also monitors the Indian Ocean Dipole, which can bring increased rainfall when it enters negative territory, while the Southern Annual Mode (SAM), which reflects conditions south of the country, is currently in positive territory, contributing to the dry weather this month.

Dr Feikema says some recent cooling of Indian Ocean temperatures suggests a reduced likelihood of a negative dipole developing during winter, while the SAM is likely to break down after the first half of July.