Map from Google - Sharm_el_Sheikh

In Sharm el-Sheikh, Egyptian resort on the Red Sea, the climate is subtropical desert, with mild winters and very hot summers.
Here are the average temperatures.
Average temperatures - Sharm el Sheikh
Sharm el SheikhJanFebMarAprMayJunJulAugSepOctNovDec
Sharm el SheikhJFMAMJJASOND
Min (°C)131416202427272827231915
Max (°C)222225303437383835322723

The rains are very rare: in practice, it never rains. Here is the average precipitation.
Average precipitation - Sharm el Sheikh
Sharm el SheikhJanFebMarAprMayJunJulAugSepOctNovDecYear
Sharm el SheikhJFMAMJJASONDY
Prec. (mm)1010100001317
Days0010000000002

In winter the temperatures are very mild, and the sky is usually clear. The rains are very rare even in this season. Every now and then, a bit of cold air can arrive, and can lower the night temperature below 10 °C, from December to February, and more rarely in March.

Spring is pleasantly warm at the beginning, in March, and it becomes hot already in April, when the weather is similar to the Mediterranean summer, while in May the heat is by now intense.

Summer, from mid-May to September, is really hot, with the sun always shining and very high temperatures. It is true that the air is usually dry, especially on hotter days, but the heat is intense, and the temperature exceeds quite often 40 °C, with peaks of 45 °C.

Autumn, in October and November, is hot and sunny; sometimes on early October the heat is still intense, then the temperature gradually decreases.

The amount of sunshine in Sharm is always great: the sun shines all year round. The sun can be obscured for a few hours by sand storms, while at times some cloud banks may pass at times from November to February.

Every now and then in Sharm the Khamsin can blow, a hot dry wind that raises dust storms, and blows especially between March and May.

Sharm el-Sheikh

The sea is very warm from June to October, so that it's possible to take long swims: the sea temperature reaches 28 °C in August and September. The sea becomes a bit cool in winter, but in the end it's not impossible for swimming, given that the temperature drops to 21 °C in February and March.
Here are the average sea temperatures.
Sea temperature - Sharm el Sheikh
Sharm el SheikhJanFebMarAprMayJunJulAugSepOctNovDec
Sharm el SheikhJFMAMJJASOND
Sea (°C)222121232426272828272524

When to go

The best times to go to Sharm el-Sheikh, for swimming and diving, are the month of April, and from mid-October to mid-November. The summer, from mid-May to September, is actually quite hot, and while the sea is pleasantly warm (especially in August and September) and you can enjoy long dives, it can be difficult to sunbathe and move outdoors during the day.
In winter the stay can be enjoyable, and the temperature is often sufficient for sunbathing, however, the days are quite short and sometimes it can be a bit cool, and as mentioned even the sea is a bit cool.