Egypt’s traditional tourist season runs from late November to late February, though in recent years Luxor and Aswan have only really been busy with tourists during the peak months of December and January. The Nile Valley is balmy throughout this winter season, although Cairo can be overcast and chilly. Winter is also the busiest period for the Sinai resorts, while Hurghada is active year round. Aside from the Easter vacation, when there is a spike in tourism, March or April are also good times to visit, with a pleasant climate.
In May the heat is still tolerable but, after that, Egyptians rich enough to do so migrate to Alex and the coastal resorts. From June to September the south and desert are ferociously hot and the pollution in Cairo is at its worst, with only the coast offering a respite from the heat. During this time, sightseeing is best limited to early morning or evening. October into early November is perhaps the best time of all, with easily manageable climate and crowds.
Weather and tourism apart, the Islamic calendar and its related festivals can have an effect on your travel. The most important factor is Ramadan, the month of daytime fasting, which can be problematic for eating and transport, though the festive evenings do much to compensate.