Dust storms, diving dam levels, heatwaves and fish kills marked both the start and finish of 2019 for NSW, with the eruption of mega bushfires and incessant smoke haze adding to the year-end's woes.

For Sydney, 2019 will go also down as the city's hottest in 161 years of Bureau of Meteorology records. It was also its driest year since 2005 - during the height of the Millennium Drought - said Ben Domensino, a meteorologist at Weatherzone.

On the road from Louth to Bourke in northern NSW in January, 2019. The state broke the previous record for average January maximums - set in 1939 - by more than two degrees, the Bureau of Meteorology said. Credit:Kate Geraghty

"December alone was not a standout month but it came at the end of a very hot year," Mr Domensino said. He estimates Sydney averaged 24-degree maximums this year topping 2016's 23.8C record.

Rainfall in December was just 1.6 millimetres at Observatory Hill, beating the record low of 2.8 millimetres recorded for the month in 1979.