It is a very common simplification and misconception that because summer has warmer water, it must mean less sharks. Scalloped hammerheads are migrating sharks, not stationary. The Egyptian Red Sea is in the northern 1/3 of the Red Sea. There are no scientific proof for this I need to say, because no tagging has been done (paging @bojanowski), but they seem to move around quite a lot. When water gets warmer in late spring/early summer in the central Red Sea, the big scools that gather in The Suakin Archipelago and sometimes can be seen off Sha ab Rumi and Angarosh, split and move north as far as to the Tiran Strait. For them to move up in the water column, currents are more a decider than the water temperature, but they need to be there to begin with. It is a little different from year to year and seasons differ, but generally they become much more common in Egyptian waters from June and onwards. Spring is great for hammerheads in Sudan, but not in Egypt. Now with changes to climate and the unpredictable impact it might have on fauna -- who knows what it'll be like in the future. But based on the last 25 years, give or take. If avoiding crowds is a priority, January or February is probably the best months.