NSW fire authorities are bracing for three days of sizzling heat with an extreme fire danger warning issued for numerous regions, total fire bans in force and some schools closed.

Hot and dry conditions are predicted on Monday for most of the NSW coast and the Central West with parts of the state tipped to experience severe conditions until Wednesday.

A widespread heatwave warning has been issued, with temperatures tipped to exceed 40 degrees Celsius in some areas and large parts of the state are under total fire bans.

The NSW Department of Education has closed 34 schools in areas with an elevated bushfire risk across the Central Ranges, where extreme fire danger ratings have been declared.

The temperature in Sydney is predicted to rise to 38 on Monday, while the Bureau of Meteorology has forecast extreme fire danger for the Greater Hunter, Central Ranges and Lower Central West Plains.

Those areas can expect hot and dry conditions combined with fresh and gusty northwesterly winds.

“Isolated high-based thunderstorms are possible during the early morning about the southern and central ranges, then developing in the afternoon across the northeastern ranges,” the BOM said.

“Little to no rainfall is expected with any thunderstorm activity.”

The NSW Rural Fire Service says extreme fire danger stretches across much of the state.

A total fire ban is in effect for the Greater Hunter, Northern Slopes, North Western, Upper and Lower Central West Plains, Central Ranges and Southern Ranges zones.

In the ACT, the Bureau of Meteorology forecasts a maximum of 29 on Monday, 25 on Tuesday, and 20 on Wednesday.