Winds

The distinctive long shape of the Red Sea, bordered by low arid coasts with high mountains rising some twenty miles inland, dictates in some measure the direction of winds, which tend to blow parallel to these coasts, either from a NW or SE direction. These winds differ significantly in the southern and northern areas of the Red Sea, and in the south show a seasonal variation due to the movement of the convergence zone between the wind systems of the northern and southern, hemispheres.

Although the Red Sea is well to the north of the equator, the ITCZ moves into this area to reach its farthest position north in July, around 12°N. At this time of year the ITCZ marks the boundary between the SW monsoon of the Indian Ocean and the prevailing NW winds of the northern Red Sea. During these summer months NW winds blow down the entire length of the Red Sea merging into the SW monsoon in the Gulf of Aden.

In winter the ITCZ lies well to the south of this region, but there is another unrelated convergence zone which lies around 18°N from October to May and marks the boundary between the SE winds in the southern part of the Red Sea and the NW winds of the northern section. This convergence zone is usually marked by cloudy skies in contrast to the ubiquitous sunshine prevailing in the region as a whole. This convergence zone is associated with rain and drizzle.

SE winds predominate from October to January in all areas south of the convergence zone. From January to May the SE winds may not penetrate quite as far as the zone itself, but still predominate in the most southerly areas and in the Strait of Bab el Mandeb. These winds are strongest from November to February, averaging around 20

knots, but gale force winds of 30 knots and over occur fairly frequently. September and May are transitional months with lighter winds. In the Strait of Bab el Mandeb, a funnelling effect occurs which increases the wind speed at all times of the year, but especially in the winter months November to March, when it is frequently 25 knots or more.

In the northern part of the Red Sea from around 20 eN, winds from theN toNW predominate in all months of the year, being stronger in winter than in summer. However, in the most northerly part, the Gulf of Suez, winds are more frequently over 20 knots from April to October with the highest frequency of gale force winds during this time. The Gulf of Suez is the only part of the Red Sea to be affected by depressions moving east across the Mediterranean.

Although the Red Sea winds are on average light to moderate, periods of complete calm do occur, sometimes for several days at a time. No tropical storms have been recorded in any part of the Red Sea. There are, however, two strong winds occur-ing in this region. The haboob is a short squall of over 35 knots blowing off the coast of Sudan between S and W, raising lots of sand and dust. Haboobs occur particularly in the Port Sudan area and are most common between July and September. The other wind is the khamsin, a strong dry S to SE wind, which blows off the land in Egypt and causes sandstorms. It occurs most commonly between February and May.

All of these winds, which bring sand and dust, reduce visibility considerably, often to less than 100 feet, especially near the coast. On the other hand, due to the special refraction conditions prevailing in the Red Sea, land and lights are often visible for much greater distances than normal, up to 100 miles away. This effect can also affect the horizon, raising or lowering it, which can produce errors in astronavigational observations, up to 20' error in longitude and 10' error in latitude. This phenomenon can affect observations taken before and after noon in different ways and can produce the impression of an apparent cross-current. It is thought that refraction is less at twilight and in the early morning, so therefore the taking of star sights has been recommended in this region. A brilliant luminescence sometimes occurs in the Red Sea making the water appear shallower. With the presence of unlit reefs extending far offshore in several places, these conditions may explain why so many yachts came to grief in this region in the past. Satellite navigation has improved safety considerably, but navigation should still be treated with due caution as most charts do not agree with satellite observations and the positions of most dangers are therefore approximate.

The Red Sea area is a hot arid region with a low rainfall. The average temperature is very high, around 30 "C, but often reaches over 40 °C in the day and even temperatures exceeding 50 eC are not uncommon. Temperatures are lowest in winter in the more northerly part, dropping to 18°C in the Gulf of Suez on a winter night. This contrasts with the southern areas of the Red Sea, where in August the temperature is over 40 eC by day and does not drop below 32 °C even at night, which can easily lead to heat exhaustion in unclimatised people. Care must be exercised in this area, especially on metal yachts, because the temperature of a steel deck can easily rise to a blistering 70 °C.

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