Tropical Cyclone Gita has strengthened to a severe category three storm and is set to further intensify as it makes its way across the Pacific.
WeatherWatch last night said the cyclone, which has already caused considerable damage and flooding in Samoa, was likely to become a category four in the next 24 hours.
And according to Niwa, a potential second tropical cyclone was developing to the west and northwest of Gita. The new cyclone would be called Hola.
WeatherWatch analyst Philip Duncan says the first cyclone is to reach Tonga tomorrow afternoon or evening.
He's expecting damaging winds with gusts over 200kmh, waves over 10 metres and heavy rain.
Duncan says cyclones have a mind of their own so forecasters will need to wait another day or so before picking whether Cyclone Gita will affect New Zealand.
Meanwhile, New Zealand's summer continues to be put on hold — the country is in for yet another drenching as the super-soaker weather system shows no sign of easing.
A severe thunderstorm watch is in place for parts of the country today and MetService is warning people to be prepared for heavy rain.
Heavy rain could hit much of the North Island and the top of the South Island, MetService said.
"Rainfall of this intensity can cause flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips," MetService said.
"Driving conditions will also be hazardous with surface flooding and poor visibility in heavy rain."
It was a wet and muggy start to the weekend for the North Island, with humidity levels sitting at 100 percent in parts of Northland yesterday. There was 72.6mm of rain recorded as falling in Mahia, in the Hawke's Bay region, in the 24 hours to 5pm yesterday.
Almost 53mm of rain fell in Kerikeri in the same 24-hour period. Auckland didn't escape unscathed, with a weather station in Warkworth recording 43mm of rain.
Gita was set to pass near Niue last night before heading just to the south of Tonga, where there was a chance of sustained wind speeds reaching more than 150km/h and waves over 10 metres.
In a statement WeatherWatch said Tonga could face coastal inundation, rain, flooding, storm surges and wind damage.
WeatherWatch said Gita was now much more powerful than recent Cyclone Fehi, which smashed a large swathe of New Zealand 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.
Sustained winds over 150km/h and gusts over 200km/h were forecast for mid next week, by which time Gita was expected to sit out at sea south of Fiji.
The cyclone's forecast track turns clockwise before it starts moving westward rapidly next week.
This would take it north of New Zealand and close enough to seriously monitor, WeatherWatch said.
WeatherWatch said multiple reliable models suggested that Gita would track further southward towards the New Zealand area around next weekend or early the following week.
"It's still far too early to know if it will directly impact New Zealand - it remains one to watch and WeatherWatch.co.nz hopes to have more specific details this Monday about whether or not this will be something for New Zealanders to seriously focus on," WeatherWatch said in its statement.
"As of Saturday night it was looking increasingly likely that it would come into the New Zealand area around next Sunday or Monday. This may still change - it's not locked in."
According to Radio New Zealand Pacific, a state of disaster has been declared in Samoa after Gita caused high winds, widespread flooding and power outages on Friday night. There were also reports of uprooted trees and roofs being torn off in the Pacific nation.
RNZ reported the Samoa disaster management office saying more than 200 people were in evacuation centres around the country.
The Samoa Observer said there had been no reports of casualties.
