The MetService has today issued several rain warnings for the West Coast with WeatherWatch.co.nz reporting that close to half a metre of rain is being predicted for some parts of the lower South Island.

MetService says up to 400mm of rain is possible between Milford Sound and Franz Josef from 6am Saturday until 6pm Monday.

WeatherWatch.co.nz head weather analyst Philip Duncan says this is an extraordinary amount of rain and trampers in the area should be aware of the approaching storm.  “While this part of the world is used to receiving torrential rain this is certainly at the higher end.  We advise trampers, tourists and locals to be aware of the approaching heavy rain”.

Mr Duncan says the deep low responsible for the rain will bring rain band after rain band to the region.  “It’s a three day assault as the low churns slowly by in the Southern Ocean.  A large high to the north and the east of the South Island means the rain bands will slow down even more as they approach the Southern Alps”.

And it’s this high pressure in the north and east that means yet again rainfall will be limited to drought regions in the north.  “Central Otago may see some rain this weekend but dry regions in the north will only see shower activity”.

“However we are expecting a ‘gap’ in the highs over northern New Zealand next week which may allow a rain band to move through around Tuesday, however the long run of dry weather isn’t yet finished for northern regions with high air pressure returning later next week”.

WeatherWatch.co.nz says high air pressure acts as a barrier, either stopping rain bands altogether or lowering cloud heights which usually results in much lighter precipitation.