A La Nina is almost certain to develop in the Pacific this summer, as all eight models used by the Bureau of Meteorology anticipate threshold levels for the key climate pattern will be reached or exceeded by next month.

The bureau's latest fortnightly assessment of conditions in the Pacific and Indian oceans rates the likelihood of a La Nina this summer at about 70 per cent – triple the usual level – prompting it to issue a La Nina alert on Tuesday.

During La Nina years, eastern Australia tends to have wetter than usual summers, as equatorial trade winds strengthen, shifting rainfall westwards.

While the added cloud cover can moderate temperatures, there is also an increased chance of prolonged warm spells for south-eastern Australia during La Ninas, the bureau says. The cyclone season can also be more active than usual.