How was it formed and what did it look like?
The Red Sea was created, like many another sea in the world by the movement of ground planes of the Earth's face 25-30 million year ago. At that time the Arab peninsula (Saudi, Yemen) started to part from Africa along a thin break line which was filled, in a very short time , by the oceans water. That way a very thin ocean was formed, much thinner than the Red Sea of today.
Mother nature did not stop at that. 20 million years ago another geological movement started, the Arab peninsula which was parted from Africa started to move to the north. That movement struck resistance in Turkey and swung to the east, so another break line was formed going all he way from Mount Chermon in the north part of Israel through the Jordan valley to the Dead Sea and from there through Eilat and Aqaba through the Gulf of Eilat to Ras Muchamad at the southern point of Sinai.

Today we have 3 ocean bodies that together are called The Red Sea but in reality they are different in age, structure and the way they were formed. Today the majority of the movement is in the Gulf of Eilat, where Jordan and Saudi Arabia are moving to the north while Israel and Sinai stays in one place. The young age of the Gulf of Eilat is what make it so deep, 1000m in Dahab and 1800m north of the Straits of Tiran. On the other hand the old Gulf of Suez is relatively shallow, 85m max. depth.

The island of Tiran and Snapir block the entrance to the Gulf of Eilat. A chain of reefs connect them with Arabia in the east and Sinai in the west. the straits of Tiran (approx. 6 km wide) are located east of Tiran island. The four patches of reefs in the straits have claimed many ships over the centuries, and even today many captains cross the straits only in day time. the reef patches, Gordon, Thomas, Woodhouse and Jackson are separated by deep rifts 40-80m deep and the tides create strong currents between them. There are only two channels considered safely navigable : Enterprise Passage - between Gordon reef and Sinai's shore (1200m width and 300m deep) and Grafton Channel Between Jackson reef and the island of Tiran (800m width and 70m deep). East from Snapir to Saudi the max. depth is 10m.

Weather
The Sinai peninsula is a part of the arid belt of deserts that encircles the globe in the northern hamesphire. Meteorological speaking Sinai can also be divided to 3 climate zones: the east coast of the Gulf of Suez, the mountains of southern Sinai and the west cost of the Gulf of Eilat. In winter the weather systems responsible for rain in the Mediterranean do not reach below 31°N. Only the occasionally strong systems that reach below that latitude cause rain in Sinai and most low pressure systems cause sandstorms around Sinai.
Low pressure systems developing in the Sahara desert draw hot dry east winds from Asia which cause dramatic temperature rises frequently accompanied by sand storms. Those same periods may also see lows developing over the Red Sea, bring moist cold air from the south and creating clouds, haze, electrical storms and very occasionally rain.

The western shore of the Gulf of Eilat is in the influence of the topography of the Syrian-East African Rift, the ocean and Sinai mountains. The area can experience changes between north and south due to the prevailing north winds which bring in dry desert air. This air becomes progressively moisture-laden as it descends the gulf. The prevailing northerlies funneled to the gulf by the Rift's Arava Valley are only slightly influenced by offshore wind in an easterly direction during the day and westerly direction at night.

Going south along the gulf, the open sea exerts an increasing profound influence upon the prevailing northern winds. The famous, and rare, southern storms, which always occur during the summer, can reach a maximum velocity of 8 to 9 on the Beaufort scale. The northern land mass is the primary influence over temperature in the gulf, but this influence diminishes to the south as you approach the open sea.

The open sea's moderating effect creates an interesting temperature pattern: maximum summer temperatures are lower in the south while minimum temperatures are higher in the north with the opposite during the winter when maximum temperatures are higher in the south and minimum temperatures are lower in the north. In any event the coldest month in the year is January while the warmest are July and August.

Water temperature are higher in the north part of the Gulf of Eilat then in the south of Sinai with the lowest temperatures in February and the higher in August and September. On the average water temperature range from 20°C to 26°C and are not affected by daily atmospheric temperature of passing weather systems.

Most divers, when asked to compare their local diving conditions with those in the Red Sea, find it a 'Paradise' with clear visibility (20-80m), little wave action, and warm temperatures all year long.