The flooding of the Georgian capital of Tbilisi was unexpected, sudden and made worldwide news, not least because it released a zoo full of wild animals into the city. Where though, could such an inundation come from?

The River Mtkvari is Tbilisi's main water artery and it divides the city, but it was not that river that flooded. The River Vere, normally a small western tributary to the Mtkvari, suddenly had to cope with a major fall of rain, and couldn't.

Saturday afternoon was not extraordinary: the city reached 29C in a steady southeasterly breeze. Clouds built, but they didn't look threatening. Unfortunately out to the west, they were.

Zoo animals on the loose amid deadly floods

With cloud bases at about 1,500 metres above the ground, one particular thunderstorm kept growing upwards until its top reached 11,000 metres. This was enough to produce vast amounts of rain, all falling over one small area.

This fed the River Vere which burst its banks, flooding the road, sweeping away cars and at least one small house, and flooding many other homes, not to mention smashing open the zoo.

Tbilisi is surrounded by hills and Georgia is mountainous. Thunder in the mountains is often a warning of flash flooding in the valleys.

There are more big thunderstorms brewing in eastern Turkey and drifting into Georgia during Monday. Thankfully it looks as though they will stay well to the west of Tbilisi.