One of the country's biggest weather forecasters is predicting the potentially devastating Oma will skirt New Zealand.

Tropical Cyclone Oma lashed parts of the Solomon Islands and Vanuatu at the weekend and New Caledonia yesterday, cutting power, toppling trees and flooding streets.

The storm system is tracking south, but WeatherWatch analyst Philip Duncan expects it will miss New Zealand. However a new weather system was expected to form at the weekend that could create pockets of severe weather.

"There's a large area of low pressure forming this weekend which sometimes means the weather can be dry, calm and non-eventful but for others it can be severe weather."

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Duncan said it was still unclear where the severe weather would be, but said if there was a big low over New Zealand only a third of the country would be affected by it.

"It might mean a rain warning maybe up in the mountains where no one lives or it might mean a rain warning in the middle of one of the biggest cities we've got. That's what we're not sure about."

Computer models were still showing there could be anywhere between 20mm and 200mm of rain in some parts of New Zealand, which Duncan said could be the difference between a normal weekend or massive storm.

Meanwhile MetService was still unsure about the direction Tropical Cyclone Oma would take and did not expect to have a clear indication until Thursday.

The delay is due to Oma is still moving slowly from the north west of New Caledonia and is yet to gain momentum which allows the models to track onto it and gauge what it's going to do, Metservice meteorologist Tui McInnes said.

"As it starts moving south it will start to get into the stronger wind system which is actually what will help us get an idea of what it's likely to do."

McInnes said at this stage it looked it would be Thursday when they would have a better degree of confidence about which direction it would take.

"At the moment there's still quite a wide variation in potential positions where it could end up."

There are several options at the moment including it hitting New Zealand or doing a u-turn towards Australia.

McInnes had more confidence in a secondary-low that was expected to hit New Zealand at the weekend bringing with it rain and severe weather.

Depending on where the rain and severe weather hits, it could put a dampener on some of the massive outdoor events planned across the weekend.

Six60 is playing in what is tipped to be the biggest ever outdoor concert for a New Zealand band at Western Springs on Saturday night and the 20th Splore music festival is being held at Tapapakanga Regional Park with many attendees camping onsite.

Six60 promoter Dave Munro said they were feeling extremely confident about the concert, which would go ahead rain or shine.

"We've been watching the weather for sure and we have contingencies, but at this stage we are ploughing towards the day and planning like it's going ahead as it should be."

MetService urged people to keep up to date with the weather warnings.