The coast of Sudan is about 650 km long, and runs along the Red Sea. It is hot and arid: Port Sudan has a temperature of 23°C in January and 34°C in July, with a mean annual rainfall of 94 mm. The hinterland is high from south to north, but there is a coastal lowland consisting of broad pediments that descend from mountain fronts. There are several watercourses, but rivers flow only briefly after rare rain, and many do not reach the sea. Tectonic movements have continued through Quaternary times, and there are emerged coral reefs along the coast. Salinity is high (sometimes exceeding 40‰) in the Red Sea, where coral reefs are abundant, many of them with sand cays.
Winds and waves on the Red Sea are mainly northeasterly and easterly. Tide ranges are very small: Port Sudan has a mean spring tide range of 0.1 m, which is obscured by sea level fluctuations of 1 m above and below mean sea level, resulting from changes in barometric pressure and onshore and offshore winds....