The remnants of a tropical cyclone that has battered Samoa, Tonga and southern Fiji is scheduled to arrive here in the next 12 hours.
MetService meteorologist Nick Zachar said the system was northwest of New Zealand at 5am and was moving "pretty quickly" southeast towards the top of the South Island.
"We expect it to hit the Farewell Spit area and move across the top of the South Island from about 7 to 8pm."
The storm was re-classified as a former tropical cyclone about 1am.
The transition happens when storms enter cooler, drier areas.
"But while it is no longer classified as a cyclone, it is still a strong storm.
"At the moment the winds are not too strong but we expect them to pick up to 130 to 140 km/h, from Taranaki south to Canterbury, and reach 150km/h in Westland and the Canterbury High Country."
One of the biggest concerns was 9-10m seasapproaching the Cook Strait to the Taranaki coast.
"These waves won't reach the shore at that height, but there is still a risk of coastal inundation, especially in the Kapiti Coast area," Zachar said.
Rain had set in from Manawatu south to north Westland overnight, and another rainband was due over Canterbury today.
Falls had not been too heavy overnight, when a maximum of 70mm fell in some areas.
More than 100mm is expected through the day andup to 200mm in some areas the storm will hit.
Severe weather warnings remain in place for areas from Taranaki south to Canterbury.
Gita is expected to bring heavy rain causing slips, rapidly rising streams and rivers, and flooding.
Severe gales with damaging gusts are expected, so people are advised to secure property and items that may be blown away by strong winds.
Coastal inundation is possible with high tide overnight Tuesday and before dawn on Wednesday, because of the combination of tides, low air pressure, strong onshore winds and large waves of more than 6m in places.
For the North Island, coastal areas from Raglan southwards to southern Wairarapa are most at risk.
For the South Island, the risk of coastal inundation is greatest for areas from Buller and North Canterbury northwards.
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.
Area: Nelson and Buller
Valid: 14 hours from 7am to 9pm Tuesday
Forecast: Expect 150 to 200mm of rain to accumulate in Nelson west of Motueka, and 90 to 150mm elsewhere. Peak intensities of 20 to 30mm/hr possible.
Area: Marlborough including the Kaikoura Coast
Valid: 15 hours from 7am to 10pm Tuesday
Forecast: Expect 150 to 200mm of rain to accumulate about higher ground, and 90 to 140mm elsewhere. Peak intensities of 20 to 30mm/hr possible.
Area: Wellington and Kapiti Coast
Valid: 15 hours from 1am to 4pm Tuesday
Forecast: Expect 75 to 100mm of rain to accumulate. Peak intensities 20 to 30mm an hour during the morning. Lighter rain is expected from late Tuesday afternoon to midnight Tuesday.
Area: Canterbury Plains (excluding Christchurch) and High Country, the ranges of Westland
Valid: 27 hours from noon Tuesday to 3pm Wednesday
Forecast: Expect 150-200mm of rain to accumulate during this period about Canterbury High Country, and 90-120mm elsewhere. Peak intensities of 2030mm/hr possible about Canterbury High Country.
Strong wind gusts could damage trees, powerlines and unsecured structures. Driving may be hazardous, especially for high-sided vehicles and motorcycles.
Area: Taranaki, Taihape, Whanganui
Valid: 10 hours from 3pm Tuesday to 1am Wednesday
Forecast: Severe gale north to northwest winds gusting 120km/h in exposed parts of North Taranaki, but damaging gusts of 140km/h in exposed parts of South Taranaki, Whanganui and Taihape.
Area: Manawatu, Kapiti-Horowhenua, Wellington and Wairarapa including the Tararua District
Valid: 8 hours from 7pm Tuesday to 3am Wednesday
Forecast: Severe gale north to northwest winds gusting 120km/h in exposed places, but 130km/h in Wellington on Tuesday evening.
Area: Nelson and Buller
Valid: 8 hours from 2pm to 10pm Tuesday
Forecast: Severe gale east to northeast winds with damaging gusts of 130-140 km/h in exposed places.
Area: Marlborough including the Kaikoura Coast
Valid: 12 hours from 3pm Tuesday to 3am Wednesday
Forecast: Severe gale southeasterlies gusting 120km/h or more in exposed places.
Area: Westland and the Canterbury High Country near the Alps
Valid: 13 hours from noon Tuesday to 1am Wednesday
Forecast: Severe gale southeast winds with damaging gusts of 150km/h possible in exposed places.
Area: Canterbury from Banks Peninsula northwards
Valid: 8 hours from 7pm Tuesday to 3am Wednesday
Forecast: Severe south to southeast gales gusting 120km/h in exposed places.
Whangarei: A few showers, turning to rain afternoon, easing evening. Northerlies becoming strong morning, easing evening. 28C high, 19C overnight.
Auckland: A few showers developing morning, then a period rain afternoon, easing evening. Northerlies becoming strong morning, easing evening. 28C high, 19C overnight.
Tauranga: Periods rain, more persistent in the evening. Northerlies becoming strong in the afternoon, easing overnight. 26C high, 20C overnight.
Hamilton: Cloudy, with a period of rain afternoon. Northerlies becoming strong morning, easing late. 28C high, 18C overnight.
Napier: Cloudy periods, chance evening shower. Northerlies becoming strong. 31C high, 20C overnight.
New Plymouth: Periods rain, easing evening. Northerlies rising to gale in the morning gusting 140 km/h. 26C high, 19C overnight.
Wellington: Rain, with heavy falls, especially in the morning. Southerlies, changing gale northerly gusting 130km/h this evening. 22C high, 14C overnight.
Nelson: Rain with heavy falls. Gale easterlies gusting 140km/h, changing northwest this evening. 22C high, 16C overnight.
Christchurch: Rain, with heavy falls from afternoon. Southeasterlies changing strong southwesterlies evening. 16C high, 11C overnight.
Dunedin: Periods of rain from late morning, with possible heavy falls from afternoon. Southerlies tending southeast late morning, then strengthening. 14C high, 11C overnight.
Police could be seen cordoning off a street in the area.