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Persian Gulf Weather - Shamal

The prevailing wind in the Persian Gulf is the northwester, called the shamal. The direction of this wind changes with the trend of the coast. A shamal may be expected at Jashk about three days after it sets in at Abu Shahr. On the Arabian coast its average direction is from north to northnorthwest, and on the west coast of Oman west-northwest, shifting to southwest near the entrance to the gulf.

On the Persian coast its direction is northwesterly southeastward to Ras Jabrin; northwest to west-northwest, thence to Jezirat Sheikh Shuaib; westerly off Jezirat Kais; and west to southwest from Jezirat Farur to the entrance to the gulf. In the northern half of the Persian Gulf the shamal blows about nine months in the year and is sometimes very strong in April. It is almost incessant during June and part of July (called the barih or 40-days' shamal), seldom exceeding a moderate gale in force and at times quite light. Its general duration is three days, but it may last seven days. The worst shamals often last only one day, and sometimes only a few hours.

During a shamal the air is generally very dry, with a cloudless but generally the air Is so loaded with dust from the Mesopotamian deserts that it is very thick. This makes navigation very dangerous, the white surf on the beach being often seen, while the land is obscured. In the Shatt al Arab it is often so thick that neither bank of the river is visible. Far off the land vessels' decks and rigging become coated with a fine impalpable dust.

During a shamal the air is generally very dry, with a cloudless sky, but in the winter these winds are sometimes attended by rain squalls, and often with thunder and lightning. The wind veers a few points during the 24 hours, blowing more off the Persian coast at night and more from the sea by day. A shamal may set in at any hour of the day or night, and generally does so suddenly.In winter, during a kaus or southeasterly gale, be prepared for a sudden shift to the northwest, especially at night, as the shamal is then often very strong.

The worst of the shamal is usually soon after the beginning, but the shamal of from two to three or five days' duration has been found, sometimes, to be strongest about the middle of its continuance. The shamal does not always extend over the whole gulf, and often lulls for a short time about daylight. In summer, shamals rarely exceed the force of a moderate gale (7), but in winter they are often fresh gales (8) or at times hard gales (9). It is generally advisable for a steam vessel of small power to obtain anchorage, if possible, during the strength of a shamal, as little or no headway will be made against it; the Persian coast and islands offer many suitable places of shelter.

A heavy swell from the northwest, especially in the southern part of the gulf, is often the precursor of a shamal, although such a swell sometimes occurs without any wind following it. Some of the severest winter shamals set in during fine weather, and give no warning except a heavy bank in the northwestern quarter an hour or two previously, which rolls down, and the air gradually becomes thick, though this sometimes occurs without any wind following. Such a warning should, however, not be neglected.

During the winter, southeasters, called a kaus, or sharki, alternate with the shamals; they also follow to a certain extent the trend of the coast, but only have any great force from December to April. The kaus is generally accompanied by thick, gloomy weather, with hard squalls, often much rain, and sometimes thunder and lightning. It seldom lasts more than 3 days, and its strength is generally a moderate gale (7), but at times it is a fresh, or even hard gale (8 or 9); the strongest often last only one day. This wind is generally strongest on its last day.

In winter, especially in the southern part of the gulf, strong northeasterly winds, called nashi, are experienced; they are accompanied by dark cloudy weather, and generally rain. The natives make a distinction between this wind and the kaus. The air is sometimes thick before a nashi, caused by the dust blown off the land. The wind often blows from three to five days, but frequently only one day; after the first day the air becomes clearer, possibly owing to rain on the land. The nashi blows in gusts with frequent lulls, and, if lasting three days, is strongest on the third day. The barometer is not affected by a nashi, being generally high; but if so, it falls a little when the wind is over.

The southwester. called suhaili, is much feared, as it blows into nearlv all the sheltered anchorages on the Persian coast. It lasts generally only a few hours, and often follows the kaus, but sometimes occurs after fine weather; it is accompanied by rain, and is preceded by masses of clouds rising from the south, with lightning. It occurs infrequently, and only in winter, but it blows all over the Persian Gulf.

At the change of the seasons in autumn, very severe squalls may be expected, called "laheimar" by the Arabs. The air is often very clear about the time of these squalls, and it does not appear that they are from any special direction. According to the Arabians they are experienced between the 15th of October and the 5th of November, during which time no native vessels put to sea until a squall is over. If they do not occur before the 5th of November, the Arabians consider that there will be none until the ordinary bad winter weather sets in. An unusual degree of electrical action is noticed, and St. Elmo's lights have been observed on board ship at this season.