Well, to start from the basics...temperatures are the reason weather even exists. If there was no sun to heat the earth (and unevenly, at that), there would be no weather. This is because temperature differences create pressure and air density differences, and those are what cause weather to occur (think Low Pressure, High Pressure, etc).
Well...it so happens that Temperature and Pressure are directly proportional (known as the Ideal Gas Law in Physics). If the temperature goes up, so does the pressure. Think of a water kettle on the stovetop with boiling water inside. Why does it whistle when the water is boiling? Because the heated water in the container caused high pressure...which had to escape out the little whistle on top.
So, as widespread surface temperatures rises, widespread upper-level HIgh Pressure gets stronger. In this case, temperatures topping out at 125*F Monday Afternoon in Needles, California (just south of Las Vegas) have largely contributed to very strong High Pressure over the Southern United States (known as the Subtropical High Pressure). Wind flow has been directed around this Subtropical High Pressure to force Tropical Storm Danielle well south of the Texas Gulf Coast.
So, blistering hot temperatures in the desert do have a purpose.
- Dan, the Weatherman