As temperatures climb on another early-season total fire ban day for much of NSW, the latest fuel moisture maps show the region around Sydney is at least as dry as during big bushfires in 2013 - but three weeks earlier in the year.

The maps, compiled by Rachael Nolan from the University of Technology and University of Wollongong researchers, show forest fuel moisture levels are continuing to decline, elevating the risk of major fires without significant rain.

"It's quite incredible," Ross Bradstock, director of UoW's Centre for Environmental Risk Management of Bushfires, said, noting that even typically rainforest-type areas are showing a rapid drying out.

"You're kicking up dust when you'd usually be picking off leeches."