Tomorrow is looking good for thunderstorms to form in some parts of the South Island. A low pressure system will form just east of the South Island tomorrow afternoon with cold air higher up in the atmosphere moving in from the west. Behind the low a cool south to southwest change will develop triggering some thunderstorms.

WeatherWatch.co.nz says the most likely places to see storms are south of North Canterbury on the east coast. The West Coast may also see a few storms during the day at first in the morning for Fiordland then further north towards evening in Buller.

Hail may form in any storms that do develop tomorrow with a potential for hail of a large size of 15 to 20mm plus falling in an area south of Banks Peninsula through into South Canterbury.

To get into slightly more detail for the east coast of the South Island, the thunderstorm risk begins early afternoon for parts of inland Southland and then for most of Otago with a tendency for storms to form more in the eastern part of the district. The chance of storms happening is fairly good here.

Mid to late afternoon the risk moves into South and Mid Canterbury particularly in inland areas however storms may spread towards the coast. Finally early evening a chance of storms develops in North Canterbury as the southerly change mentioned above moves in. The risks of storms happening is fairly good in Canterbury with perhaps a slightly lower risk as unstable conditions move into North Canterbury however only slightly lower.

Weather analyst Aaron Wilkinson from WeatherWatch.co.nz also notes that with the wind profiles through the atmosphere tomorrow there is also the outside chance of a funnel cloud or small tornado forming somewhere in Canterbury, “The atmosphere is looking a little more conducive to them happening then other storm set ups I’ve seen”. The chance of this actually happening Aaron says is fairly low however and if it does happen it may go un noticed anyway.

Further north into Marlborough thunderstorm chances look lower due to surface northwesterly winds keeping moisture levels low, and thunderstorms need relatively good surface moisture to grow.

WeatherWatch.co.nz