"Sydney has recorded an average maximum temperature of just 24.5C so far this summer, more than one degree below the average of 25.6C," said Tom Saunders, Senior Meteorologist at The Weather Channel.

"Just over a week into February and the city has been particularly chilly with an average so far for this month of just 23.7C.

"Hours of sunshine have also been below normal."

On average there had been four hours of sunshine a day, three hours cloudier than normal.

"The unseasonably cool temperatures are the result of our second consecutive La Ni�a summer," Mr Saunders said.

"La Ni�a refers to a cooling of the equatorial Pacific Ocean, which typically brings above-average rain and below-average temperatures to northern and eastern Australia."

The weather is set to stay cool and cloudy for the remainder of the week with widespread rain expected across NSW?from today to Sunday.

"By Sunday night most of central and southern NSW?can expect at least 10mm of rain, but the region south of about Wollongong and east of a line from about Wilsons Promontory to Canberra should receive over 50mm," Mr Saunders said.