Egypt receives fewer than eighty millimeters of precipitation annually in most areas. Most rain falls along the coast, but even the wettest area, around Alexandria, receives only about 200 millimeters of precipitation per year. Alexandria has relatively high humidity, but sea breezes help keep the moisture down to a comfortable level. Moving southward, the amount of precipitation decreases suddenly. Cairo receives a little more than one centimeter of precipitation each year. The city, however, reports humidity as high as 77 percent during the summer. But during the rest of the year, humidity is low. The areas south of Cairo receive only traces of rainfall. Some areas will go years without rain and then experience sudden downpours that result in flash floods....
http://touregypt.net/climate.htm