Persistent and heavy rain at Flemington on Tuesday morning has made this the second wettest Melbourne Cup day on record.

An untimely low pressure trough sweeping over Victoria his been producing rain and thunderstorms over Melbourne this morning.

Image: Rain over Melbourne on Tuesday morning.

As of midday, Melbourne had collected 35mm of rain since nine o'clock this morning. Based on historical daily rainfall observations in the city after 9am on race day, this is now the second wettest Melbourne Cup day on record. 

The previous highest amount of rain recorded during the 24 hours from 9am on Cup Day was 46.5mm in 1942, when the race was run on a Saturday.

While rain is expected to ease this afternoon, showers and thunderstorms will still be affecting central Victoria at 3pm and may affect the race.

Track the showers in the lead-up to this year's Melbourne Cup race here: http://www.weatherzone.com.au/radar/vic/melbourne/128km