Temperatures are expected to be high across the state. Mildura is expected to get a high of 38 degrees on Saturday.
The October record for Mildura was 40.2 degrees, while the last time it got this hot in the first week of October was 2015.
Mr Delamontte said the last time Melbourne had a run of hot days this early in October was 2015 when the city topped 25.8 degrees.
“At this stage we expect to see a more significant cool change move through probably later at some stage during Sunday,” Mr Delamontte said.
Monday is expected to be closer to the early October average, with temperatures in the high teens.
Mid-spring also brings the risk of deadly asthma attacks brought on by pollen.
The state’s chief health officer Brett Sutton on Monday warned that the grass pollen season had officially begun.
Forecasts for the thunderstorm asthma season started on Monday and will continue until the end of December.
“We want everyone, particularly those with asthma or hay fever, to be as prepared as they can for the grass pollen season,” Dr Sutton said.
“Those at risk should always follow their asthma or hay fever treatment plan.
“Where possible, people with asthma and hay fever should also avoid exposure to springtime thunderstorms, especially the wind gusts that precede them.”
Nine people died in the spring of 2016 in a freak asthma thunderstorm. Thousands of people had breathing difficulties.
It is thought to be triggered by thunderstorms with high amounts of grass pollen in the air.
People who are not diagnosed with asthma are still at risk. Dr Sutton warned all Victorians to be alert for wheezing, shortness of breath, tightness in the chest, and persistent coughing.
“It can be sudden, serious and even life-threatening,” he said.
Visit Better Health for more health information on pollen season.
Rachel is a breaking news reporter for The Age.