Parts of Sydney have had their biggest dump of rain in five years, helping to soak gardens still dry after a prolonged spell of below-average falls.

Mona Vale in the city's north collected 112 millimetres of rain overnight, the most for that site since 2013, Brett Dutschke, senior meteorologist with Weatherzone, said. The 56mm of rain at the airport was the most in 21 months.

The rain dump was caused by a southerly change that slowed as it moved up the coast, creating a relatively small region of converging winds "with a fair bit of moisture", he said.

Sydney itself collected 53mm, the second-most in the past nine months.

Showers will ease through Tuesday with a chance of regathering tomorrow morning, although without the intensity of those overnight, Mr Dutschke said.