New South Wales is enduring sweltering temperatures and thunderstorms to open the first day of summer. A hot air mass and clearing skies have caused the mercury to soar over central and northern parts of the state today. Bourke in the state's northwest reached 42.5 degrees, making it the towns hottest December day in three years. This also makes it the third consecutive day above 42 degrees, which also occurred for the last time in 2009. Albion Park in the state's east reached 37.9 degrees, making it the hottest December day in eight years. The heat has also been associated with large amounts of moisture, making it feel up to three degrees warmer in some parts. However, due to this moisture, thunderstorms are again likely to flare up across the state this afternoon and evening. This is good news due to several fires burning across the state. Although lightning has been the cause for some of these fires, thunderstorms today are likely to contain more rainfall than the last few days. Falls of up to 30mm are possible in the state's south and along the southern and central slopes and ranges. These thunderstorms may become intense, with flash flooding and damaging winds a risk. The heat and thunderstorms should contract into the state's north on Sunday as the trough moves north, with inland locations like Walgett, Moree and Gunnedah again likely to creep into the low 40's.