Tropical Cyclone Donna has been downgraded to a Category 4 this morning, and New Caledonia's main centres look likely to avoid any major impact, the MetService says.

Donna was classified as a Category 5 cyclone by the Fijian Meteorological Service last night, but MetService forecaster Nick Zachar said it had weakened and was now a 4.

However, he said another storm was brewing east of Fiji, which was likely to be upgraded to a cyclone, dubbed Ella, this afternoon.

Record-breaking Donna, the worst tropical storm to hit the South Pacific in the month of May, was still battering Vanuatu last night but had since eased.


"Currently Cyclone Donna is intensity Category 4 and currently at 100 knots but it is expected to weaken fairly quickly towards [Tuesday] evening. So it is starting to move slowly south, southeast, towards eastern New Caledonia. It looks like it's going to miss Noumea and skirt east of the mainland and west of Vanuatu.

"So the main centre is going to be missing most populated areas, most thankfully. But there are some isolated islands in its path."

Zachar said the cyclone is expected to weaken from here on as it had already reached maximum intensity.

The outer portion of the cyclone will hit New Caledonia later today and tomorrow, and by Thursday it will continue heading southeast before eventually hitting New Zealand's eastern coast on.

"But by then it will be an extra tropical, that means it will bring some enhanced rainfall to parts of the North Island, especially eastern parts, so mainly East Cape at the moment.

"The main impact is going to be rain related and not the intense winds at the moment." is forecasting for the tropical cyclone's remnants to hit New Zealand on Friday.

"At this point Donna will begin to transition into a new low and rapid deepening/expanding is possible to the east of the North Island. It will no longer be a tropical cyclone though."

Zachar said there was still some uncertainty as to how Donna will track and if she will veer off-course.

But overnight, a new system had begun forming east of Fiji and would likely be named as a cyclone this afternoon, he said.

"It's not going to be a very intense one, any strengthening will be gradual, but there is a decent chance of it being named Ella.

"It has intensified in the last six hours or so and so the pressure is deepening."

He said the system was very slow moving and not expected to hit Fiji today.

If the system was classified as a cyclone, it would be the second to have formed outside the usual cyclone season, which ends on April 30.

"But unofficially, the season will go as long as it needs to as long as the conditions remain; warm waters and the conducive wind conditions. It's not quite unusual but it's something we don't see every year that's for sure."

Rain was forecast for the country later this week anyway as a front heads over from the Tasman.