When you talk about average temperatures there will always be a variation depending on where you are. Temperatures are cooler along the Nile River and the Mediterranean coast. The deserts are much dryer and hotter and the further south one travels the hotter the average temperatures. Average temperatures also varies during the year. Egypt is north of the equator so its seasons are the same as our own.
Temperatures are hotter in the summer and milder in the winter.
The sand and rocks get very hot, reflecting the sun light and radiating heat. Ripples of heat waves shimmer of the surface like air above hot coals. The reflection of the sun off the sand can give you a sunburn. When there is no moisture in the form of clouds in the sky to keep the daytime heat in the air, temperatures rapidly drop after the sun goes down. There are few plants or water to store the daytime heat and the sand cools rapidly after sunset.