The big wet hammering the top of the North Island is not expected to let up any time soon.

The drizzle was expected to continue for the rest of the day before the heavens opened again tomorrow.

Isolated thunderstorms and flooding were possible across the North Island and humidity was expected to hit 100 per cent at times, according to Weather Watch.

A severe weather watch remains in place for Northland until noon today and more rain is expected in Northland, Auckland, Great Barrier Island, Waikato, Waitomo, Taumarunui, western Taupo, Taranaki and Taihape, including Tongariro National Park from 2pm tomorrow until 3am Sunday according to a heavy rain watch just issued by the Metservice.

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Another watch has been issued for Tararua, Kapiti-Horowhenua and Wellington from 6am tomorrow to 1am Monday.

Rainfall could reach warning amounts, 100mm or more in 24-hours, in all of those areas, the Metservice said.

Meanwhile, Cyclone Gita was expected to strengthen to a category 3 cyclone in the tropics but there was still uncertainty as to whether she would have a sting in her tail for this part of the world.

The newly-named cyclone lashed Samoa overnight, buffeting the island nation with winds gusting 130 kilometres an hour and rainfall totalling almost 200mm in Apia.

Gita is expected to strengthen to a category 3 as she moves towards Niue and Tonga over the next 60 hours, but New Zealand's fate remains unknown.

Cyclone Gita can be seen near Samoa in this image from the Earth Winds website. Photo / Earth Winds
Cyclone Gita can be seen near Samoa in this image from the Earth Winds website. Photo / Earth Winds

MetService meteorologist and cyclone forecaster Bill Singh said this morning it was still too early to know if remnants of the cyclone will eventually track our way.

"The next five to six days this system will still be in the tropics. Some of the models are taking it west across the Tasman, some to the southwest ... towards us."

More would be known by the middle of the week, Singh said.

WeatherWatch.co.nz said this week it was too early to confirm whether the Gita would hit New Zealand, but warned if it formed it would be "much bigger than Fehi".

Ex-cyclone Fehi smashed a large swathe of the country last week, flooding homes and businesses, stranding travellers when damaged roads were closed and causing dramatic storm surges.

The north and west of the South Island were worst affected.

A washed out road near Fox Glacier, on the West Coast, during ex-cyclone Fehi last week. Photo / Supplied
A washed out road near Fox Glacier, on the West Coast, during ex-cyclone Fehi last week. Photo / Supplied

In a post to its Facebook page about 8am, the Samoa Meteorological Service said periods of heavy rain, a few thunderstorms and a storm surge of 4 to 4.8 metres was possible in northern and southern areas.

"Potential Impact – river overflows, slippery road, poor visibility, flooding, landslide and flying objects," they wrote.

Gita was expected to be 196km southeast of Apia by 1pm today (noon NZT).

Cyclone Gita brought rain and wind to Samoa overnight. Photo / Samoa Meteorological Service
Cyclone Gita brought rain and wind to Samoa overnight. Photo / Samoa Meteorological Service

Singh said the cyclone was expected to track southeast and intensify to category 3 as it moved close to Niue tomorrow and southern Tonga late on Monday.

"At this stage the system is intensifying. The amount of time it's spending in the tropics it would be expected to strengthen. It would be at least category 3 later tomorrow or early next week."

Category 3 cyclones are when sustained winds reach at least 120km/h and gusts reach 170km/h.

Rain will also be an issue for affected areas. Cyclone Gita will settle in Niue from late tonight and even though Gita will have moved away, downpours will continue in Samoa thanks to moist northwesterlies.

Samoa Meteorological Service has forecast occasional rain, heavy at time and with thunderstorms, winds gusting to 56km/h and combined waves and swells of 3 to 3.6m tomorrow and Monday.

Gita is also expected to track to the south of Fiji after moving away from Tonga, with strong winds forecast around late Tuesday and early Wednesday, Singh said.