The rain is expected to be intense and heavy – with up to 380mm around the range and 200mm around the coast with a peak rate of up to 30mm per hour.
Flooding is likely while slips could close roads, disrupting transport routes and isolating communities, MetService said.
The red warning was prompted by an active front moving across southern and central New Zealand and preceded by heavy rain for western areas.
MetService meteorologist Andy Best said the warning was issued due to the amount and intensity of the rain.
"It is of particular concern for people who are on the roads," he said, urging anyone going away for the school holidays to check the weather conditions of their route on the MetService website.
In particular, those driving on SH6 Haast Pass, Sh73 Porters Pass and SH60 Takaka Hill were urged to take extra care.
Heavy rainfall warnings are also in place for the headwaters of the Canterbury lakes and rivers from the Rakaia river northwards, and between Mount Cook and the Rakaia river, Nelson, west of Motueka, and the western ranges of Marlborough.
Windy Wellington will live up to its name this weekend with severe north to northwest gales reaching up to 140 km/h in exposed places around the capital, and 120 km/h in southern Wairarapa.
The strong wind could damage trees, powerlines and unsecured structures, while motorists are warned of possible hazardous driving conditions, especially for those in high-sided vehicles and on motorbikes.
MetService weather warnings
Buller and Westland north of Fox Glacier: Red warning, July 15, 9pm - July 17, 6am. Up to 380mm of rain about the ranges, 150-200mm about the coast. Peak hourly rates 20-30mm/h.
Nelson west of Motueka: Heavy rain warning, July 16, 6am - July 17, 1pm. Up to 280mm of rain about the ranges with 130-180mm about the coast. Peak rates 15 to 25mm/h.
Westland south of Fox Glacier: Heavy rain warning, July 15, 9pm-July 16, 9pm. Up to 150mm of rain. Peak rates of 15 to 25mm/h. Thunderstorms possible.
Western ranges of Marlborough: Heavy rain warning, July 16, 4pm-July 17, 10am. Up to 180mm of rain. Peak rates of 15 to 25mm/h.
Canterbury lakes headwaters & rivers, the Rakaia river northwards: Heavy rain warning, July 15, 11pm - July 17, 4am. Up to 350mm of rain about the divide, up to 250mm within 20km east of the divide. Peak rates of 20 to 30mm/h.
Canterbury lakes headwaters & rivers, between Mount Cook, Rakaia river: Heavy rain warning, July 16, 4am - July 17, 1am. Up to 250mm of rain about the divide, with 150 to 200mm within 20km east of the divide. Peak rates up to 25mm/h.
Taranaki: Strong wind warning, July 16, 8pm - July 17, 3pm. Northerly severe gales gusting 120km/h.
Marlborough: Strong wind warning, July 16, 1pm - July 17, 8am. North to northwest severe gales gusting 120km/h.
Wellington, and Wairarapa south of Featherston: Strong wind warning, July 16, 3pm - July 17, 11am. North to northwest severe gales gusting 140km/h, 120 km/h in southern Wairarapa.
