Bahrain Climate

Introduction

The Bahrain islands are located in the west central Gulf some 20 nautical miles from the mainland of Saudi Arabia, the highest point being the Jebel Al Dukhan hills 440 feet (134 metres) above sea level in the centre of the main island. The airfield is located on the island of Muharraq, some 15 nautical miles from the Jebel Hills and 2.5 nautical miles to the north east of the main island and capital, Manama. Zones of agriculture and areas of date palm extend along the north and west of Bahrain which provide a local source of moisture for infrequent radiation fogs through evapotranspiration.

Outside of Manama, urban development exists in the central northern area of the main island (Isa Town & Hamad Town).

Important regional features are the dust and sand basins of Iraq some 350 nautical miles to the north west and the mountain range of the Zagros of Iran, 120 nautical miles at their nearest to the north east. These features, together with the Gulf waters have the main influence on the broadscale climate of Bahrain. The Zagros hills cause the low level winds to be directed to below mainly from the north west or south east by steering or influence on the pressure pattern. The dust bowls of Iraq and northern Saudi Arabia provide an abundance of fine dust particles easily transported by north westerly winds which cause visibility reductions at Bahrain, mainly in the months of June and July. The Gulf waters provide a low level moisture supply.

Seas are relatively shallow around Bahrain and heat up quickly in the summer to give high dew point values and humidity, especially at night. Sea temperatures may reach 35 Degrees Centigrade during the summer.

General Climate

The climate of Bahrain is an arid type; mean annual rainfall is small (70.8mm) and irregular. Broadly speaking, the year may be divided into two main climatic periods from June to September and from December to March, separated by two transitional periods April/May and October/November.

The mean number of days per annum with measurable rain of 1mm or more are 9.9 with the highest being 2 days in the month of January. Thunderstorms occur on average on 7.8 days per annum with March having the highest mean average of 1.9 days. The average number of days per annum that visibility is reduced to 1000 metres or less by fog is 6.6 and by thick dust haze is 4.5. January averages 1.7 days of fog, and is the highest monthly frequency. July has the highest frequency of thick dust haze occurrence (1.1 days on average).

The Winter Period

The winter period is the season of changeable weather when low pressure disturbances with their associated fronts transit the mid Gulf. Surface winds alternate mainly between south east ahead of these features and north west behind.

The passage of the front and troughs may be accompanied by thunderstorms and squalls. Isolated severe storms can occur. Between these periods of "weather" a high pressure ridge over and good visibility.

The Summer Period

The summer period is one of mainly cloudless skies and persistently high temperatures. A shallow dome of relatively cool moist air over the Gulf is overlaid by hot dry air causing a marked temperature inversion in the first 1000 to 1500 feet of the order of 5 to 10 Degrees Centigrade. The seasonal rise in temperature peaks in August with a mean daily maximum of 38.0 Degrees Centigrade. The extreme maximum temperatures are observed however in May (46.7 C). During June and July a period of persistently strong north westerly winds known locally as the "summer shamal" occurs and arrests temporarily the seasonal rise in temperature.

This shamal which is part of the Indian monsoon circulation is related directly to a low level jet stream concentrated near 1000 feet. This causes marked wind shears at times in the boundary layer of the order of 5-8 knots per 100 feet.

The shamal transports dust from Iraq and visibility at Bahrain on occasions is reduced to less than 1500 metres over this period mainly between 2000Z to 0600Z.

The Transition Period

The transition periods are important in two respects, the first is the abruptness of the change during October/November when first incursions of cool air from the north west occur and replace the quiet conditions of late summer. The second, and more importantly, is the spring transition.

This period is known as the sarrayat. Sudden changes in wind can occur, caused by relatively weak instability features, and low level wind shear has been observed with these sudden changes.

Average Monthly Temperatures