Cyclone Gita is forecast to continue moving west into open waters over the next couple of days, but there's the possibility it may have some impact on New Zealand early next week.
NIWA's Chris Brandalino said the eye of the cyclone was 400km to the south of the main Fiji islands, so the impact was nowhere near as severe as in Tonga.
The official forecast from the Fiji Meteorological Service was that it would remain a category four cyclone, Mr Brandalino said.
Over the next 24 hours it would move over warm water, which he said was fuel for tropical cyclones.
The cyclone could fluctuate and if it did strengthen that would likely happen over the next few days, Mr Brandalino said.
"There are these nerdy terms called an 'eyewall replacement cycle' - so basically the cycle is eyewall, that's where the strongest winds are, it's around the eye and these intense cyclones go through phases where that eyewall gets replenished, kind of like a snake losing its skin ... and that cyclone can cause for fluctuations."
Cyclone Gita is forecast to remain a strong category four until it reaches New Caledonia, before starting to take a left turn into the northern Tasman Sea where it would need to be watched for risk of heading to New Zealand, Mr Brandalino said.
"There are some indications that we could see early next week an impact here in New Zealand but it is a bit early to [say] exactly who will see the most impact or the worst impact.
"It will be early next week before something is likely to occur and over the next couple of days we will be able to fine tune that [prediction]."
He said over the coming weekend it looked like it would move closer to New Zealand, increasing humidity again for a couple of days.