Egypt’s weather is less a single climate than a set of them, laid out north to south. The Mediterranean coast at Alexandria takes about 211 millimetres of rain in a year, most of it between November and March, with wind off the sea and cool, damp winters. The Nile valley is arid and hot, and the desert either side of it is more arid still. By the time you reach Aswan and Abu Simbel, the annual rainfall is around two millimetres or none, and the summer highs are over forty degrees.
That is why advice about the seasons depends entirely on the itinerary. A week on the Red Sea is comfortable in any month. A week in Luxor in July is a test of character. A week in Alexandria in January needs a coat and an umbrella, and the rest of the country will be dry and mild at the same moment.
Winter and spring
Winter, from December to February, is the season most visitors choose. Days are mild to warm along the Nile valley and on the Red Sea, the Mediterranean gets its rain, and Cairo can be cool and grey. The catch is the nights: desert and river towns are cold after sunset, and buildings designed to keep heat out do a poor job of keeping it in.
Spring, from March to May, is the khamsin season. A hot, dry wind out of the desert blows for days at a time, raising the temperature, filling the air with sand and dust, and occasionally closing airports or cancelling boat trips. It is also the season with the clearest water on the Red Sea, so divers accept the wind as the price of visibility.
Summer and autumn
Summer, from June to August, is extreme in the interior and the south, with average daily highs above 41 degrees in Aswan, and merely hot on the coasts. Everything sensible happens at the edges of the day: monuments at six in the morning, a long rest in the middle, and the evening for walking, eating and travelling.
Autumn, from September to November, is the quietly good season. The heat is breaking, the sea is still warm, the crowds have not yet arrived, and by November the desert nights have cooled to the point where a jacket is welcome. If you have a free choice of dates and no particular attachment to Christmas, this is the window to take.
Heat, humidity and how it actually feels
Two things make Egyptian heat feel different from a European summer. The first is the dryness: in the desert and along the Nile, sweat evaporates immediately, which means you can lose a lot of water without noticing and can be badly dehydrated by three in the afternoon. Drink before you are thirsty, and drink more than feels necessary.
The second is the shade. There is not much of it, and the difference between standing in the sun and standing two metres to the left can be fifteen degrees. The whole art of an Egyptian itinerary in warm weather is finding the shade at the right times: the colonnades at midday, the boat in the afternoon, the roof terrace at dusk.
It is worth knowing one more thing about the dryness, which is that it hides the danger. You do not feel yourself sweating in Aswan the way you would in Athens, because it evaporates as it appears, and the first sign of trouble is often a headache in the late afternoon. The remedies are boring and they work: two litres of water before lunch, a hat, salty food, and a refusal to stand in the sun for an hour looking at a wall.
What to pack, and what to check
Pack for two climates, because you will probably meet both: light long-sleeved clothing for sun protection rather than shorts, a hat that survives wind, something over the face for a dusty day, and a jacket for the desert night in winter. Add reef-safe sun protection for the coast, and a windproof layer if you plan to be on the water.
Then check the forecast for the specific thing you have booked rather than for the country: the Red Sea wind decides whether a boat sails, the khamsin decides whether a desert day is pleasant or pointless, and a single thunderstorm in the hills above Luxor is the reason the Valley of the Kings has drains. Egypt does not have weather that ruins holidays. It has weather that changes the plan, if you let it.
The short version: the north coast is a Mediterranean climate with winter rain, the Nile valley and the deserts are hot and dry all year with cold winter nights, and the Red Sea coast is the one place that behaves in every month. Choose your dates by where you are going, not by the calendar.