MONSOON (KHAREEF) OVER SALALAH AND ADJOINING AREA

By: Khalid Ahmed Al-Najjar,

Met. Forecaster, Salalah Airport, Sultanate Of Oman.

The Sultanate of Oman occupies the South-Eastern part of the Arabian Peninsula and shares borders with the United Arab Emirates, Saudi Arabia and the Republic of Yemen. It extends along the Gulf of Oman and Arabian Sea, with a coastline of about 1700 km from the straits of Hormuz in the North to the Northern border of Yemen in the South. The country has an approximate area of 314,000 sq. km. The Salalah plane is a coastal area in half-moon shape about 50 kilometers long and  12kilometers wide at the center. The plane is surrounded by mountains (known as Dhofar mountain) to the North having the highest peak of 5945 feet.

During summer monsoon in this region takes position roughly along the line joining Jacobabad, Jiwani, Muscat, Fahud, west of Thumrait and Salalah and dips in to Yemen.

Satellite pictures show the cloud cover as small patch of cloud about 90miles in length and less than 50 miles in width centered near Salalah. The lowest cloud, as observed from the ground, is ragged Stratus type accompanied by poor visibility and mostly sea ward as a solid bank of fog. Above this Stratus are layers of persistent Stratocumulus. The base and amount of Stratus have more diurnal variation than Sc, the minimum coverage; together with highest base occur between 1300 LST and 1700 LST. Aircraft observations show that Sc tops are normally less than 5000 feet and no cloud occurs above Stratocumulus. During active monsoon period Stratus base may comes down to 100 feet.

Shows the marked trade wind inversion near 950 HPA and the temperature over mountain rising to 37 C before monsoon. During monsoon the inversion goes up and lies between 870 HPA to 700 HPA .The layer below inversion is always near saturation. The air is completely dry above the inversion layer.

Over Arabian Peninsula the sea level pressure is at its lowest during  monsoon period. Over Salalah plane surface winds are gentle, southeasterly 5 to 10 Knots, seldom exceed to 15 Knots., veering southwest in the afternoon with slight increase in velocity and backing southeast in the evening or night. But over Dhofar Mountain the surface winds during monsoon are always southerly with speed around 20 Knots, and exceed 30 knots at Thumrait. Over Arabian Sea the surface winds are in between 30 to 40kt due to the strong pressure gradient. Surface wind data indicate that convergence over Salalah plane and wind ward side of adjoining mountain and divergence over north of it.

The diurnal variation of temperature is very small. During the Khareef with the air near saturation both day and night average maximum temperature is 27 C with average humidity at minimum  around 85%. Average minimum temperature is 23C with average humidity at maximum around 97%. Average dew point is at approximately 23C.  

Lowest sea water temperature recorded at Salalah port is 18C and highest is 23C during monsoon season. This low sea surface temperature is due to the upwelling of sea water. If sea surface temperature is less than the dew point temperature of the air than fog and mist forms over sea and advected to Salalah plane.

Rainfall over Salalah plane and adjoining windward side of mountain is normally in the form of drizzle mixed with light rain and seldom exceeds 5mm in 24hours period over Salalah plane. Average rainfall during monsoon period at Salalah airport is of the order of 60mm with most of that (approximately 52 mm) falling during July and August. Average rainfall during this season over windward side of the mountain is of the order of 200mm, where as leeward side of the mountain and north of it practically receive no rain. The histogram of average monthly rainfall of Salalah Airport (representative station of Salalah plane) and Qairoon Hairitti (representative station of mountains) are enclosed here with.

Monsoon over southern Oman becomes active if: -   

1- Mascarene high is north of its normal position.

2- Thermal low forms over southeast Saudi Arabia and adjoining Yemen.

3- Wind speed increases over mountain and desert.

4- Monsoon low or depression formed over head Bay of Bengal and moving in west or northwest direction.

5- Trough forming over west coast of India.

Monsoon over southern Oman becomes weak if: -

1-                 Monsoon trough is east of normal position in this region.

2-                 Western disturbance passing across northern Oman.

3-                 Monsoon becomes week over India. 

All above studies shows that monsoon over southern part of Oman is an integral part of Indian monsoon and reaching here as a weak current, or we can say that southern part of Oman Comes under the outer periphery of Indian monsoon. For better understanding of monsoon over this region more surface and upper air observations are required.

 Comments | Back to Top