A weatherbomb - Storm Barra's explosive cyclogenesis

Ahead of slamming into Ireland with strong winds and torrential rainfall this morning, Storm Barra underwent something called explosive cyclogenesis. But what is this?

Cyclogenesis happens with an area of low pressure undergoes rapid intensification with explosive cyclogenesis occurring when pressure drops at least 24 millibars within 24 hours.

Storm Barra saw its central pressure drop from 1010 millibars at noon on Monday to 959 millibars at noon today. That’s more than twice the threshold to meet the explosive criteria!

Barra’s explosive cyclogenesis occurred because of an interaction with the jet stream – a ribbon of fast moving air around 5-8 kilometres high in the atmosphere.

As Barra got caught up in the jet stream, the area of low pressure was able to suck in more air making the system spin faster and lowering its pressure rapidly.

The best known cyclogenesis or ‘weatherbomb’ to hit Ireland was the Fastnet Rock storm in August 1979 where the pressure dropped by 40 millibars in 24 hours leaving 15 sailors dead.