The Tour's very first Rider Board, out of Khartoum, with information about the upcoming stages ... temperature, distance, destination, and so on.  You can see, for example, that Day Two was a ride of 148 km (about 92 miles), with temperatures ranging from 12 to 26 degrees Celsius (54 to 79  in real degrees).  Worth noting is the wind, a gusty, buffeting headwind of 30 km/hr that felt like continuously being punched in the face by the Pillsbury Doughboy for eight hours at a time. 

It would get much, much hotter than that in the Sudanese desert.  Oh, yes it would.  It would get so hot that the riders who spontaneously combusted into flames would be considered the lucky ones.