Weather: Cyclone Yasa strengthening in Pacific, 40 pct chance it reaches New Zealand

The first tropical cyclone of the season in the southwest Pacific has formed - and forecasters warn it could cause a "serious major hit" to New Zealand.

Cyclone Yasa burst into life over Sunday night and is currently a category 1 tropical cyclone, with the Fiji Meteorological Service forecasting it to grow to a category 3 by Wednesday.

According to the Australian Bureau of Meteorology, this would likely mean "very destructive winds" and "some roof and structural damage".

Based on current forecasts, WeatherWatch says Yasa will spend the next few days "spinning around in a giant circle".

"It is expected to brush Fiji so those in the area should be closely monitoring local forecasts and warnings," it says.

Will it hit New Zealand?

As for New Zealand, whether we're in the firing line is still unclear. WeatherWatch has about 40 percent confidence this low will make it to NZ, probably one week from now.

"However the storm will be going through a major structural change at this point which means a number of future scenarios are possible from a serious major hit, to a weak low that only brings some rain, to one that falls apart and misses NZ entirely," it says.

"The 40 percent confidence is based on modelling from various agencies over the past several days and reflects our current confidence."