Sweltering heat across NSW and Sydney will abruptly be whisked away by a cooling southerly buster.

A brisk southerly wind change is moving up the south coast of NSW. It should reach Sydney about 7pm, rapidly dropping temperatures from the sweltering high temperatures on Saturday (35 or so in the west) to cooler, more bearable conditions overnight and Sunday.

Thunderstorms have developed as hot, humid conditions combined with atmospheric instability. These will produce some heavy falls of rain with the slight chance of some minor local flooding.

Image: Thunderstorm cloud near Nundle that developed Saturday afternoon. Source: James Rout.

A cold front that moved through Tasmania Saturday afternoon will make its way north along the NSW coast on Sunday, bringing further rain. It should get to Sydney about the middle of the afternoon. As it moves through, some heavy falls can be expected, with rainfalls of between 10 and 20mm the likely result.

The wet conditions could make it difficult for players in the NRL game at Accor Stadium on Sunday afternoon as they try to handle the wet leather ball.