Computer models have been picking for days a rapidly forming low in the Tasman Sea this Thursday, Friday and Saturday which may become defined as a “weather bomb” says WeatherWatch.co.nz.

The term “weather bomb” relates specifically to a low pressure system that drops 24hPa in 24 hours.  “It’s the weather equivalent of having a tyre blow out” says head weather analyst Philip Duncan.  “The air pressure plummets and conditions quickly become unstable”.

Some media outlets incorrectly use the weather bomb term to describe any stormy weather however it should only be used to describe this rapid deepening of a low pressure system. 

Weather bombs in New Zealand tend to cause isolated but severe damage.  A weather bomb in Patea, South Taranaki, back in March caused extensive damage as hurricane force winds blew out roofs, walls and toppled trees – however only slightly further north winds remained light.  “These weather bombs tends to have the severe gales, or hurricane force winds, right near the centre, just like tropical cyclones. So the further away from the centre you are, the lighter the winds usually”.

So what are the chances of this low reaching this criteria?  Mr Duncan says fairly high at this stage. “The models we’re looking at show the air pressure dropping from around 1000hPa on Thursday evening to 976hPa on Friday morning, possibly lower”.

The low is expected to generate big seas on the western coastline, torrential rain for the West Coast and severe west to north west gales for eastern and central New Zealand.

“We still have to wait another day or two to confirm but no matter how you look at it, it seems likely a nasty low will develop in the Tasman Sea overnight Thursday and into Friday – then weaken across the weekend as it passes over New Zealand”.

WeatherWatch.co.nz will monitor the low and bring you daily updates.