The expected weather forecast for the hottest Halloween day on record was nowhere to be seen, according the Bureau of Meteorology.
And the warm weather is being blown away this afternoon by winds gusting in the city more than double the forecast speed.
Unholy heatwave! Halloween's record high
Those planning on dressing up for trick or treating may want to rethink some of their costumes, as Melbourne is in for its hottest Halloween ever.
"The temperature only reached 30.2 degrees at 1:40pm," a spokesman for the Bureau of Meteorology said.
"The westerly wind is causing the cool change to start to come now, as we are currently sitting at 28.4 degrees".
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Winds in the city have reached 56 km/h, topping the prediction for winds between 15 and 20 km/h. At Laverton, wind speeds have hit 41 km/h this afternoon.
Earlier, Bureau of Meteorology forecaster Peter Newham said that the hottest ever October day recorded in the city of 36.9 degrees was in 1914.
Mr Newham said the month of October was known for its extremes, and tomorrow would be a case in point.
A cool change is expected to sweep across Melbourne from late this afternoon, causing the temperature to plummet to a low of 13 degrees tonight and a top of just 18 degrees on Thursday with showers.
"There will be quite a few showers around tomorrow, particularly in the eastern suburbs, and then Friday there will be a clearing shower or two," he said.
The weather is expected to dry up for Derby Day on Saturday, with 21 degrees and sunny conditions forecast.
But punters on Melbourne Cup Day may have to re-assess their wardrobe choices.
While a maximum of 29 degrees is forecast on Tuesday, thunderstorms and showers could hit the racetrack.
"It looks like it will be warm ahead of a cool change, the timing of which is tricky to determine this far out. There could be showers and even thunderstorms with that change. It's uncertain, but potentially quite showery on Tuesday," Mr Newham said.