Maitland and Singleton are expected to swelter through 42 degree days, while Cessnock (41 degrees) and Newcastle (39 degrees) will also experience high temperatures.

Hot north-westerly winds of about 25 to 35 km/hour are expected for the morning, but will shift south-easterly into the afternoon to cool things down.

Showers are also predicted for Tuesday afternoon.

Bureau of Meteorology duty forecaster Jordan Notara said no significant frontal systems are set to come through until after Friday, meaning the cool temperatures and showers will hang around.

Showers are expected across the Hunter for Australia Day and into the weekend.

The Royal Flying Doctor Service has reminded people about the dangers of heat stress.

South Eastern Section senior flight nurse Karen Barlow said people needed to be prepared to counter heat stress by knowing the signs and symptoms and what to do if one experiences it.

Early signs include muscle cramps in limbs or stomach, dark coloured or reduced urine flow, vomiting, headaches, dizziness and fainting.

“The RFDS SE recommends common sense measures such as avoiding exercise or outdoor activity during very hot conditions, considering your health and fitness when undertaking activities in hot weather and carrying plenty of water if hiking or travelling in remote areas,” Ms Barlow said.