Sydney will experience its first decent rainfall in months with heavy showers and possible storms forecast for Friday.

The Bureau of Meteorology predicts 15-25 mm of rain will fall on Sydney, most likely in the morning. Temperatures are likely to hover between 18-20 degrees through the whole day.

It will be the first decent rain for the city's withered parks, sports fields and gardens since June 10, when Sydney received 20 mm in one day.

Weatherzone meteorologist Jacobus Cronje said the downpour would be a welcome relief.