When we were out in the centre for 3 weeks we didn't get a drop of rain, but 2 weeks later it rained in The Simpson. For the most part you should expect fine weather really.
Days are great, shorts and t shirt weather, nights get very cold out there. When we were in the desert a mate left his washing up bowl out full of water...it had frozen the top layer of the water overnight. I walked around heaps in double pluggers, so ground for the most part shouldn't be muddy unless it has rained or does rain whilst you are out there. There's plenty of prickles on the ground in some areas of the desert, so watch what footwear you choose to wear.