Key Points:

Residents in parts of the country have been warned to brace for widespread flooding, slips and fast-rising rivers as a power-packed, mid-week weather system hits. The MetService today reported that, when a deep low pressure system arrives on Wednesday, some exposed places in affected areas of the South Island could receive more than triple the agency's warning criteria level of rainfall. A large front the MetService called a "combination of significant weather features" with "explosive cyclogenesis" was forecast to move on to the lower South Island late Tuesday, then cross much of the South Island on Wednesday and the rest of the country on Thursday.

Each of the fronts were expected to bring periods of heavy rain to western areas and strong winds in the east. For Fiordland and Westland, there was moderate confidence that heavy rain warnings would be required tomorrow. For Fiordland, Westland, Buller, northwest Nelson and the Tararua Range, there was a high level of confidence that rainfall accumulations would meet warning criteria on Wednesday and Thursday. For Southland and Clutha, there was a moderate confidence of rainfall reaching warning criteria on Thursday. "Our warning criteria is 100mm of rainfall in 24 hours, but some of these ranges and more exposed area could get 300mm in 24 hours," MetService forecaster Lisa Murray said. "So this is a really significant event rain-wise because of those accumulations and there is probably going to be widespread flooding at times, slips and rivers rising rapidly." While Kiwis understood how severe these systems could be, Murray said tourists in affected areas like Fiordland and along the South Island's West Coast needed to be aware of what was coming. "The tourists don't really understand that when we get a deluge of rain like this, just what impacts it can have on the country and on the microclimates within New Zealand." It wasn't just hard rain on the cards - strong winds could exceed wind speeds of 120km/h. Strong to gale northwest winds were likely to affect eastern areas of the South Island and southern North Island for extended periods later in the week. For Wairarapa, Wellington and the east of the South Island, there was a high chance of severe northwest gales on Wednesday and Thursday. "We are talking about damaging winds here... we are talking, tie down the trampoline," Murray said. "Most of the South Island will be affected, especially those high country areas." For coastal Southland and Stewart Island, there was moderate confidence that westerly winds will rise to severe gale at times on Tuesday. By the end of the week, the dominant weather over New Zealand would return to a southwesterly flow.

Main centres: this week's highs and lows

Auckland: Tues: 23C/16C Weds: 24C/17C Thurs: 23C/14C Fri: 21C/14C Hamilton: Tues: 25C/12C Weds: 25C/15C Thurs: 22C/10C Fri: 21C/8C Tauranga: Tues: 28C/15C Weds: 27C/17C Thurs: 24C/12C Fri: 23C/12C Wellington: Tues: 21C/16C Weds: 20C/15C Thurs: 19C/10C Fri: 17C/11C Christchurch: Tues: 29C/14C Weds: 26C/12C Thurs: 21C/7C Fri: 17C/8C Dunedin: Tues: 20C/11C Weds: 17C/9C Thurs: 15C/8C Fri: 15C/9C