The tens of thousands of frocked-up punters heading to the Melbourne Cup tomorrow can bet on grey and drizzly conditions.

To avoid a wardrobe malfunction of feathered fascinators wet and limp from rain, the Bureau of Meteorology is urging revellers to pack a poncho or umbrella with up to 33 millimetres of rain expected to drench the city over the next 24 hours.

The Melbourne weather bureau is predicting the wild weather will ease just in time for the main event.

“The heaviest rain for Cup Day is expected in the morning,” senior forecaster Michael Efron said.

“We’ll see the rain becoming more extensive n the early hours of Tuesday and this will continue until about 11am … we could see [up to] 15 millimetres in those few hours.

“However, the conditions look like they will clear up around lunch time which is good news for those heading to Cup Day.”