Spring (March to May) and autumn (September to November) are the finest, with warm days, calm seas and comfortable water for diving and snorkelling. Summer is very hot and the sun is fierce, though the sea stays inviting and evenings are pleasant. Winter is mild and sunny by day but can be cool and windy, and the water turns chilly, so bring a wetsuit and warm layers for desert trips.
The Sinai sun is strong year-round and intense in summer, with little natural shade at dive sites and on desert trips. Carry water, use high-factor sunscreen, a hat and sunglasses, and plan open-air excursions for the cooler morning or late afternoon.
The Red Sea is beautiful but must be respected. The Blue Hole in particular has a deadly reputation for divers who exceed their training, so stay within your limits, dive with a reputable centre, watch for currents when snorkelling and never swim out alone.
Dahab and the South Sinai resort coast are calm and used to tourists, but the wider Sinai interior is more sensitive. Take desert and canyon trips with established local operators, keep your passport for the road checkpoints, and follow current local advice for any travel further afield.