People get confused about this all the time. The reason is that temperature vary a lot in Egypt. November is usually still pretty balmy and air is nice. Get into December and things change. By February water around Sinai can drop down to 20 degrees and air plus wind can be chilly. In April/May it turns and by July it is 27-28 degrees in the water and the air is hot, sometimes too hot. Then if you go to the Southern parts of Egypt (still Northern Red Sea) , Rocky Island, Zabargad, St Johns, you can add a couple of degrees at any certain point of time compared to the Gulf of Aquba.
Then a BIG factor, is how many dives/day and for how many consecutive days do you intend to dive? There is a big difference if you do 3-4 dives/day for a week on a liveaboard or go resort diving/day boats doing two dives a day for 4-5 days. I'd say it is the difference between a shorty or a full, snug fitting 3-5 mm suit in high summer.
It is not unusual to see professionals diving dry in the winter months. You can see tourists in shortys in winter too (not common though).
Personally I dive Egypt in the summer months and sometimes in fall for longinamus encounters. I always do 3-4 dives/day and for at least a week. So I spend 3.5-4ish hours a day in the water for a week or more. I dive in a full, snug fitting 5 mm suit and sometimes gets a little chilly at the end of the last dive. But mostly ok.