Because we’re at the mercy of a heatwave that is going to get worse before it gets better.

Dubbo’s maximum temperature on Thursday was 39 degrees, just after 2pm.

Friday will be a little more mild, with a predicted top of 37 but the mercury will nudge back towards 40 on Saturday and break through that mark.

And at the moment, it is predicted the daily maximum temperature for each day through until Wednesday will be somewhere in the 40s.

To put it bluntly, even by summer standards, it is going to be a disgusting few days, with an emphasis on Wednesday when the minimum temperature will be a balmy 28 degrees.

And while we may have experienced days and nights this hot before, the prolonged nature of this week's heatwave makes it dangerous to the health of people and animals.

A high pressure system over the Tasman Sea is to blame, with the system directing a hot air mass across Australia's southern and eastern states this week.

This stagnant weather pattern will remain largely unchanged until the middle of next week, resulting in the conditions where both maximum and minimum temperatures are likely be more than 10 degrees above average at times.

NSW Health has warned residents to try to stay cool and remain hydrated through the day.

"People can be unprepared for the first heat spike of summer, so we are reminding them to take safety measures against the effects of overheating and sun exposure," Ben Scalley, Director of Environmental Health, said in a statement.

"It's important people keep up their water intake, stay cool and avoid strenuous physical activity in the heat of the day.”