Residents in NSW sweating through conditions resembling those in the tropical north will have to wait days for relief from stifling humidity.
A trough over the state's inland led to Sydney briefly exceeding Darwin's humidity on Thursday, with the hourly dew point temperature reaching a record level of 25.9C at Observatory Hill near the city centre at 11am.
The dew point represents the amount of moisture in the air and higher temperatures point to greater moisture levels in the atmosphere.
Any dew point temperature above 24C is considered "oppressive", causing uncomfortable conditions for most people and leading to potential heat stress.
Morgan Pumpa, from the Bureau of Meteorology, said the northwest NSW town of Bourke had the same humidity as Norfolk Island on Friday morning, an anomaly caused by the inland trough on top of tropical thunderstorms.
Penrith, in Sydney's west, recorded a 26.1C dew point at 10.30am on Friday, pushing the "feels like" temperature up to 30C - nearly four degrees above the actual air temperature.
In the city centre, the dew point reached 25.2C shortly before midday.
The humidity has also brought thunderstorms to inland NSW and Victoria, with chances of localised heavy rainfall from the Riverina into western NSW and from the Victorian eastern ranges into Gippsland.
"Humidity along the coast is more common than inland, where we have more of a drier heat," Ms Pumpa said.
"So at the moment it's not just what we do have, it's what we don't have."
Chances of rain will increase over the weekend, including isolated showers and thunderstorms across southern and western NSW.
A southerly change is forecast to bring relief early next week, bringing down humidity levels and delivering up to 15mm of rain to Sydney on Monday.
