Thunderstorms are a potent and potentially deadly force of nature. Lightning, flash flooding and powerful wind gusts all have the capacity to kill.

But rarely can one individual storm have had such deadly consequences as the one which hit Mecca around 14:30 GMT on Friday.

The number of dead and injured continues to rise, following the collapse of a giant crane onto the Grand Mosque.

Mobile phone images appear to show a crane adjacent to the mosque being struck by lightning and authorities have said that winds in the area were gusting to 83 km/h.

The autumn season is the period when thunderstorms are most likely in Mecca.

Of the 20 days on which thunderstorms occur each year, half of those will be during the months of September, October and November.

This particular storm was one of several which occured during Friday afternoon, developing over the Asir Mountains, south of the city, before drifting northwards.

These storms developed because of a combination of favourable atmospheric conditions.

Firstly, the area of low pressure, which had spawned dust storms across the Levant in previous days, drifted southwards into northern Saudi Arabia.

A low pressure area over Sudan also moved northwards. Low pressure makes the atmosphere unstable, and the heat and high humidity close to the Red Sea combined to develop a line of major storms.

Theoretically, a tower crane should be earthed against the risk of a lightning strike and be able to withstand gusts of 83km/h.

Investigators will, no doubt, be looking at the construction of the damaged crane.

With an ongoing risk of storms in the next few days, they will also have to examine the integrity of the other cranes surrounding the site.

Source: Al Jazeera